# Another Knucklehead Build



## mayhugh1

After completing the Quarter Scale Merlin, I took several months off to work on a number of projects that had piled up around the home and shop. High on my to-do list was assembling a number of backup XP computers while the parts were still readily available. I've had an ongoing concern that my ten year old homemade shop computers as well as those running my wife's embroidery machines have been living on borrowed time. I could, if necessary, convert my Tormach to Linux-based PathPilot, but the hardware associated with my Wabeco lathe is still tied to Mach3. I also built up a couple Windows 7 machines so I could have at least one foot inside the modern world. I tried migrating to Windows 7 entirely, but I wasn't able to get some of my ancient CAD/CAM software nor my wife's embroidery software running on their 64-bit operating systems even in their so-called compatibility mode. Replacing all that software was pretty much off the table for me.

Committing to a new long term engine project involved a lot of procrastination and eventually came down to a decision between Ron Colonna's 270 Offy and Draw-Tech's Knucklehead. In order to shake the bugs out of the new shop computers, I modeled the Offy's crankcase as well as the Knucklehead's cylinder head assemblies in SolidWorks. I felt the Offy would probably be of wider interest to others since I'm not aware of any detailed published builds for it. In the end though I felt like I needed more time to consider some alternate approaches to the Offy's one-piece crankcase, and so for now I chose the Knucklehead.

I really liked the looks of Draw-Tech's CAD rendered Knucklehead but wasn't even aware of its existence until I came across Steve (Driller1432)'s HMEM thread:

http://www.homemodelenginemachinist.com/showthread.php?t=24705
http://www.homemodelenginemachinist.com/showthread.php?p=301687#post301687

His successful build validated the plan set and proved the model could be made to run using the original Harley timing. So I decided to do a thread on its build and, along the way, fill in some of the machining steps that Steve left out to perhaps encourage others to build one of their own. There was so much effort put into that engine's drawings that it seems a shame to allow them to languish on the forum's download site. 

Even though it has only two cylinders, this engine isn't a beginner's project, though. It's considerably more complex than a Hoglet or even Jerry Howell's V-twin, but the finished result will be more reminiscent of an actual full-size engine.

I decided to begin the build by machining the exterior components of the head assemblies which I had already modeled. This included the heads, cam brackets, valve boxes, and rocker arm boxes. At first glance, the head assemblies appear to be the most complex parts of the engine, and their individual parts must fit precisely together.

My first step was to get hard copies of the pertinent downloaded pdfs since I've never been comfortable with working directly from drawings on a computer screen.

http://www.homemodelenginemachinist.com/downloads/draw-tech-297.html

Because some of the key drawings were intended for E-size sheets, I dropped a flash drive off at our local copier store so they could print them out for me on their huge cut sheet printer while I ran some errands. When I returned, though, I was informed that the store's policy was to not copy or print out copyrighted material. They pointed out the title blocks in the lower right hand corner of the drawings that contained words to the effect that the drawings were not to be reproduced without written consent from the original owner. No amount of common sense reasoning could get me past the clerk I was dealing with. Instead of coming back later when someone a little less literal might be on shift, I printed the large size drawings out in poster board mode on my home printer and then carefully taped them together to create the large sheets.

It'll feel good to be making chips again, but with only two cylinders to deal with this time there won't be as many of them. -Terry


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## mayhugh1

Both heads were machined from a chunk of 6061 from my scrap pile. Each head requires several operations, and their order is important to accommodate the work holding of the complex shape as it evolves. The head's 1/32" thick cooling fins are set on 3/32" centers and will wind up too fragile to be reliably gripped in a vise, and so their machining will be left to the very end. Most of the fins are deep enough that they will have to be cut with a slitting saw rather than be slot-milled with an end mill. In order to avoid folding any of the fins over, their external contours will be fully machined before performing any of the slitting operations.

The first operation included machining the outer perimeter of each head as well as its bottom surface. The bottom surfaces were finish machined right up front so they could provide references for the top-side finishing operations. Each bottom-side finishing operation included a hemispherical combustion chamber and a .010" deep mounting recess for a head gasket. In retrospect, I could have increased the depth of the recess somewhat to help locate the cylinder to the head.

The top surfaces were roughed in and then finish machined using a couple angle block setups in the mill vise. Care was taken to get these angles correct since they will affect the fits of the valve boxes to the rocker box. I made a few minor changes to the original drawings in order to provide some additional stock around the mounting screws in the rocker and valve box covers. I also machined the heads to use long-reach Viper spark plugs since I had a couple spares left over from the Merlin project. The original plan set assumes the use of more economical scratch-built plugs for which drawings are supplied. In any event, it's important to machine the plug's mounting surface and to drill and tap its hole in the same setup in order to obtain the best seal around the plug. I've also learned from bitter experience to not bevel the edge of the mounting surface around the top thread of the spark plug hole in order to clean up the burr that sometimes ends up there. Even with a spark plug washer, that extra bit of metal around the hole's top thread helps to seal the plug.

I made a couple minor changes to the vertical fin design to improve the cosmetics of their intersections with the valve cover boxes that will be machined later. When it came time to machine the heads for the valve guides and seats, however, I couldn't find the drawings for the guides nor the upper and lower valve spring perches in the documentation I had downloaded. Steve was kind enough to email me a copy of the drawing that he had used. After some deliberation I opted to combine the guide and seat into a unified cage to improve my chances of obtaining a concentric valve/seat combination. This was very easy to do, but the next head machining step required the cages to be machined and finally installed before the ports for the intake and exhaust tubes could be drilled and reamed.

The cages themselves were machined from C544 which is a free machining phosphor bronze alloy that I've used for the seats and guides in nearly all of my engines. I didn't have any stock of the proper diameter on hand, and so I ordered a short length from McMaster-Carr. I used to buy this material from Enco and then later from MSC (at much higher cost) after they acquired and killed off Enco. MSC, however sells their rod stock only in six foot lengths, and for this project I needed only six inches. What I received from McMaster Carr was clearly marked C544, but its outward physical appearance didn't match the other C544 material I had in my collection. Its spiral-colored raw surface looked more like 632 or 932 rod stock. I've included a photo comparing it with the piece of C544 that I eventually had to purchase from MSC.

The o.d.'s of the cages turned easily enough, but I couldn't control the chatter of the 7/16" carbide ball mill used to turn the i.d.'s. I managed to dig up some scrap cages from an earlier project, and their interiors were smooth with no signs of chatter. I thought I'd better cut some test seats before installing the cages in the heads. Sure enough, the material was so hard that even my carbide seat cutter left unacceptable chatter marks that would have ruined any chance of obtaining a usable seal. I made five trial seats and could not achieve an acceptable result using any of my manual piloted seat cutters no matter what I tried.

I reluctantly ordered the C544 from MSC, and what arrived appeared to be identical to the smaller diameter material I was used to working with. The cages machined beautifully with no internal chatter, and the test seats cut buttery smooth. The cages were sized for a light press fit in the aluminum heads, and high temperature Loctite retaining compound was used to insure they stay in place. A 9/16" standard end mill was used to plunge cut the major bore in the head for the cage, and its actual measured i.d. was used to set the target o.d. for the turned cages.

Two final head machining steps remain. These include drilling the ports for the intake and exhaust tubes as well as cutting the various cooling fins. - Terry


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## Cogsy

Looking forward to another fantastic build and write up on this one.


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## petertha

Looking forward to the build Terry.

OnlineMetals has different flavors of bronze. I bought a stick of their SAE660 C932 as well as C544 Phosphor Bronze for different purposes. They were different for sure & OLM packages the vendor spec sheets with the order. Or at least they do that on mine maybe because I'm across the border.

http://www.onlinemetals.com/merchant.cfm?id=850&step=2&top_cat=850
http://www.onlinemetals.com/merchant.cfm?id=1801&step=2&top_cat=850


Speedy Metals has 932(SAE 660) & 954 (aluminum bronze) in round, not C544 phosphor bronze. http://www.speedymetals.com/c-8382-round.aspx


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## Ghosty

Terry, another one I will be following. 
I know what you mean about the older computers, I run one running XP Pro as I have 3 film scanners($2500 each) that only have software for XP, I also still run AutoCAD 14, way to expensive to replace as I only use it about 20 hrs a year now. I have 2 motherboards, processers and ram put away in case it dies.

Cheers
Andrew


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## driller1432

Terry
Nice to see another build of the knucklehead your a master, it will be an awesome build. 
Stephen


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## bouch

mayhugh1 said:


> After completing the Quarter Scale Merlin, I took several months off to work on a number of projects that had piled up around the home and shop. High on my to-do list was assembling a number of backup XP computers while the parts were still readily available. I've had an ongoing concern that my ten year old homemade shop computers as well as those running my wife's embroidery machines have been living on borrowed time. I could, if necessary, convert my Tormach to Linux-based PathPilot, but the hardware associated with my Wabeco lathe is still tied to Mach3. I also built up a couple Windows 7 machines so I could have at least one foot inside the modern world. I tried migrating to Windows 7 entirely, but I wasn't able to get some of my ancient CAD/CAM software nor my wife's embroidery software running on their 64-bit operating systems even in their so-called compatibility mode. Replacing all that software was pretty much off the table for me.
> 
> -Terry



This one is going to be interesting.  Loved the Merlin Build, and I just downloaded the plans for this one from your link.

RE: old XP machines.  Unless you need physical connections which don't come on modern machines (like a 25 pin printer port), you should be able to run XP as a virtual machine on a more modern computer.  I have a friend who works for a company that still runs applications on Digital VMS based machines, and they use Windows-based servers running Virtual VMS machines.  Something you may want to consider next time some of your hardware fails.


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## wirralcnc

Terry.
I was driving home from work today and was thinking, not heard much from Terry for a while after the merlin build.  Glad to have you doing another build, I will be watching with interest.

Robbie


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## kuhncw

Terry,

I'm looking forward to your Knucklehead project and the education your build logs provide.

Thanks.

Chuck


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## Naiveambition

Oh terry we r thinking alike,  must be the Texas air:thumbup:   
I too was in the debate of what to build next, and my choices were the knucklehead and the 270 offy also.    And the main reason why I decided to make the leap above my pay grade was from watching you build your Merlin engine,  i thought thru your thread, man this guy built this in the same amount of time I built my ma deuce,.  So naturally I feel compelled to push myself again. 
    Though my first choice would be the offy to see you build as there are none it seems finished threads out there, I too understand about the offy crankcase after looking thru the plans , but none the less I will be watching this post closely as I can so I know where I'm going on my  knucklehead motor.  

Mike


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## mayhugh1

I found the most difficult step during both modeling and machining the heads to be the drilling of the ports for the intake and exhaust tubes. It's the locations of these two corner features that make the front head different from the rear head. Some difficulty arises because neither hole is parallel nor perpendicular to any axis or feature on the head. The drawings contain the angles needed to locate the two components of each hole's axis so it will properly intersect the area behind the valve seat. It's also cosmetically desirable for the tubes to wind up centered between a pair of radial fins that will be machined later. Touch-off points for the actual drilling operations, though, aren't provided nor are they easily specified because of a lack of suitable reference features in the machining plane. I ended up using some shaky geometry involving a couple corner vertices that I indicated under a spindle microscope.

The heads were supported in a two axis swivel vise which, in turn, was mounted on a heavy duty sine plate. This setup provided the compound angles needed for all four machining operations with just a single reversal of the part in the swivel vise. The ports were through-drilled between the appropriate corners on the heads and their adjacent valve cages using a quarter inch drill. Counter-bores were plunged for the intake/exhaust tubes using a 3/8" end mill. Pucker factor was in the red during all four drilling operations since it would have been easy to ruin the heads which were so close to the finish line. An assembly drawing (lots of these are provided) shows these tubes being held in place with setscrews which I'll likely augment with Loctite. I like to test my engines' valve seals by pulling vacuums through the ports behind them. Any clearances between the port tubes and the heads are potential leaks.

In order to machine the cooling fins I found it convenient to first machine an arbor on which to support the heads using their already drilled and tapped head bolt holes. The slots between most of the fins were cut with a 1/16" thick slitting saw. The 2-3/4" diameter saw used in my 1-1/4" diameter arbor was barely able to cut the vertical slots to their full depths because of clearance issues between the arbor and various features on the head. I switched to a 1-1/8" diameter (1/16" thick) Woodruff cutter on a 1/2" arbor for the three vertical slots in the center of the head. This was necessary to avoid gouging the valve guides which, at this point, had been permanently installed. Had I followed the drawings and used separate guides and seats, the guides could have been temporarily removed for this operation and allow the same slitting saw to be used for all the vertical slots.

The same saw was also used to cut the slots between the radial fins around the lower perimeter of the heads. The depths of these slots depend upon the particular side of the head, but all are contoured to follow the rounded corners of the heads' exterior perimeters.

Somehow I managed to complete both heads without any significant screw-ups. These little workpieces ended up with a lot of machining, and there'll be several more parts just like them to come. It's the detail added by all those operations, though, that will add the interest and realism to the finished result. - Terry


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## Draw-Tech

Hi Mayhugh
 Jack here, It's so good to see members interested in my model. All should learn from your detailed description of every thing. Awesome Looking forward to your build, and will follow. I am now designing the Flathead next. 
  Great Work
Jack
Draw-Tech


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## mayhugh1

Each head assembly will include a pair of valve boxes, a rocker box, and a rocker shaft support bracket. All the boxes, and especially those covering the valves, will require quite a bit of machining in a number of different setups.

The easiest to make parts in the head assemblies are the support brackets which will be bolted in extra wide slots between the vertical cooling fins. They were machined in cookie sheet fashion, and only a couple additional operations were needed to drill and counterbore mounting holes for their 2-56 cap screws.

The valve boxes are considerably more complex, and the left and right boxes on each head are mirror images of each other. The plans includes drawings for both-handed parts as well as a number of other mirrored pairs. In my experience, this is fairly unusual with model engine plans and is very much appreciated. One of my struggles with the Howell V-twin involved machining its fairly complex mirror-image carbs from the single-handed drawing provided.

The interiors and outer perimeters of all four boxes were roughed out in the first mill setup in which eight 1-72 mounting holes were also drilled and tapped. There isn't much space on the floors of these boxes for their 2-56 mounting cap screws, but the heads have to be counterbored so they won't interfere later with the valve spring mounting pads. The first secondary operation included the removal of a fillet left on the rear of the box by the first operation in an area where a sharp inside corner is required. A third setup was needed to finish machine the boxes' interiors and provide the clearances needed around the rocker shafts and arms. The boxes were trial fitted to the heads, and the hole locations for the rocker shafts were transferred from the installed support brackets before drilling and reaming the holes through the rear walls of the boxes.

The machining for the valve box covers included drilling and counterboring the holes for the 1-72 cap screws. The covers were flipped over, and clearance channels for the rocker arm assemblies were machined. A nice touch is that the top surfaces of the covers are not flat but are designed with slightly contoured surfaces on a large diameter radius. In order to machine these contours, the covers were bolted to the valve boxes, and the boxes were held in a vise for machining. While still in the vise, a flange was machined into the nose of each assembly for a close fit into the rear of the rocker box. - Terry


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## johnmcc69

That's some really nice machining going on here, nice work & set-ups.

 I really like the bead blasted finish, what are you using for media & at what air pressure?

 John


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## mayhugh1

John,
The media is glass bead from a local Harbor Freight. I'm not sure of the grit - it was the only thing they sold about 5 years ago when I bought it. There's no pressure regulator on the air supply feeding the cabinet and so it's running 90-120 psi. - Terry


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## mayhugh1

The rocker boxes protect the rocker arm hardware and enclose the top-end lubrication system. In addition to the large bolts that protrude through the side covers, it was the shape of the rocker boxes that resulted in the term 'knucklehead' becoming associated with this particular engine.

Whenever I make parts like these on my Tormach, I can't help but feel a healthy respect for the skill and concentration that would be required to manually produce them on a rotary table. In my case, the rear and peripheral surfaces of both boxes were machined at the same time before flipping the individual workpieces over to hog out their interiors. I took a few liberties with the original interior shape but paid close attention to the clearances required around the heads of the 8-32 button fasteners that will be used to mount the boxes to the heads. I initially left some extra stock on the bottoms of the boxes so the mounting feet could be trimmed to their final lengths in a separate operation that included trial fitting them to the valve boxes on the heads.

I believe the original design intent was that a pair of -014 o-rings would be used to seal the entries of the valve boxes to the rear of the rocker boxes. The parts drawings include the necessary clearances for them, but they don't appear on the head component assembly drawing that I downloaded. I do plan to add them because otherwise the rocker boxes will almost certainly leak since oil will be sprayed onto the rocker shafts right where they exit the rear of the rocker boxes. The assembly drawing does, however, show equally important o-rings underneath the heads of the rocker bolts which will seal them to the front cover.

As it turned out, I managed to make the machining of the relatively simple covers more complex than that of the boxes. The covers were initially milled out in typical cookie sheet fashion according to their drawing, but the generous fillets around their front faces left little material around their perimeters for any secondary work holding. Not only did the rears of the covers need to be faced to bring them to their final thickness, but I decided to add a snug fitting .020" high boss on the rear surface of each cover to positively locate it to the box. Since I had some 1 mm o-ring cord on hand, I also decided to mill an o-ring groove around the perimeter of the cover in order to seal it to the box.

I bolted each partially machined cover to a piece of MDF with its unfinished rear surface facing upward. When clamped in a vise, the workpiece was securely supported with its finished front surface facing down but perpendicular to the mill's spindle. However, the axes of the cover weren't perfectly aligned to the mill table, and the final fit of the cover to the box critically depended upon this alignment. Fortunately, Mach3's g-code library includes G68 which is capable of rotating the machine's coordinate system to that of a misaligned workpiece. It was easy to calculate the precise angle of the part in the vise by measuring its corner coordinates under a spindle microscope. This was my first experience with G68, and to my amazement the snug fitting covers turned out to be near perfect fits to the boxes.

With the covers in place on the boxes, the locations of the holes for the rocker bolts were transferred from the rear of the boxes to the covers, and the holes were drilled, reamed, and counterbored for the bolt heads.

The final operation on each rocker box was the drilling of a pair of holes through its bottom for the push rod tubes. The axes of these holes were, of course, at compound angles with respect to the surfaces of the box not unlike those for the intake/exhaust ports in the heads. Fortunately, the drawings supplied touch-off points for the centers of these holes which greatly simplified the drilling operations. Strangely, the holes didn't result in the rocker boxes becoming mirror images of one another as I might have guessed. Since I haven't and don't plan to model very much more of the engine's assembly, I hope this doesn't come back around and bite me later. - Terry


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## petertha

Nice work Terry. 

I just finished doing some O-ring work for my radial. Fortunately while the part was still in the lathe, I was able to test fit its mating part only to determine the fit was going to be way too tight. So I was able to modify a bit on the fly. With only 1.5mm diameter cord, it was pretty teeny amount. For O-ring parts like your cover where you want it to have a certain fit or seal, do you dry run the groove width & depth on a piece of scrap first with your O-ring type/durometer in hand? I found some info online but it was a bit generic - mostly hydraulic seal related. I have one more sealed part sealed to make, so thought I'd pick your brain.


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## mayhugh1

Peter,
Normally, I just follow the published recommendations for the groove size, but in this case I cut several trial grooves in some scrap to determine the best height for compressing the o-ring. I ran a narrower groove than typically recommended because I wanted the o-ring to stay put so I wouldn't have to deal with it during what might later be some tricky assembly with the rocker  arm components. This meant also making the groove deeper than normally recommended. I ended up with only .005" compression and a 100% filled groove.  - Terry


p.s. I was following your project during my hiatus - nice work.


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## e.picler

Hi Terry!
Congratulations for the wonderful building. This is really awesome work.

I realized you use a CNC machine.
I'm curious about what CAM software are you using to generate the G code.

I also have a CNC milling machine and today struggling to develop the Fusion 360 Post Processor for the milling CNC control. Not much Autodesk assistance here in Brazil.

Thanks,

Edi


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## mayhugh1

Edi,
I'm using Solidworks2010 for CAD and Sprutcam7 for CAM. Sprutcam is distributed in the US by Tormach. - Terry


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## kuhncw

Terry,

I just received some 7/16 C544 bar from Online metals.  The bar has the spiral marking I'm used to seeing on 660.  The 544 from Online Metals measures just about exactly 0.437.  I've always found 660 bar to be oversize.  For example, my 3/8 660 measures 0.410.    Did your C544 from McMaster measure 0.75 or was it oversize?  

Thanks.

Chuck


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## petertha

I'll have to look at my OLM 544 & 660. But what is the significance of the spiral marking?


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## mayhugh1

Chuck,
The rod stock that I received from both MSC and McMaster-Carr were, in fact, .002" undersize.

Peter,
I'm not sure what that spiral coloring is.

Terry


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## mu38&Bg#

Spiraling like that on bronze is continuous cast.


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## e.picler

mayhugh1 said:


> Edi,
> I'm using Solidworks2010 for CAD and Sprutcam7 for CAM. Sprutcam is distributed in the US by Tormach. - Terry



Thanks Tarry!
I will start using Sprutcam very soon. There is a Tormach here in Brazil. I will have the training a couple weeks. They will also supply the Post Processor for the milling machine and the lathe. They told me that the Sprucam is easier to use then MasterCam.

Edi


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## mayhugh1

I next worked on the rocker shafts since their fits in the head assemblies will provide some feedback on the construction's accuracy so far. The shafts are large custom machined bolts that support the rocker arms which themselves are fairly complex three-piece subassemblies. These multi-part assemblies were necessary to solve an otherwise impossible rocker arm installation, but their individual components require careful machining.

I turned the bolts from 303 stainless and polished their heads to match the rocker box covers. Their lengths were also polished to reduce wear on the rocker components. The ends of the bolts were lathe threaded to insure the threads were straight and concentric with the shafts. These bolts, which thread into the rocker support brackets, pass through cylindrical tunnels in the valve boxes. The backsides of the heads, which fit into recesses in the rocker box covers, are grooved for o-rings which seal them to the covers. Fortunately, all four of the bolts installed with no issues.

The real test, however, was a check of the concentricity of the shafts to the circular tunnels inside the valve boxes. The cylindrical components of the rocker assemblies rotate on these shafts inside the tunnels, and there's little clearance. In fact, the drawings call out the same diameter for the o.d.'s of the rocker arm components as for the i.d.'s of the valve box tunnels. Their actual concentricity, however, has been affected by at least a dozen machining and assembly steps in getting to this point. Even with perfect machining, the diameters of the rocker components will have to be reduced to prevent binding.

In my case the concentricity was determined by trial-and-error machining the o.d. of a bushing that was slipped onto each of the installed rocker bolts. I reduced the diameter of the bushing until it spun freely on the worst-case shaft, and then I reduced its diameter another four thousandths for margin. I used this diameter to modify the design of the rocker arm components before they were machined. In my case, including the margin, the diameter was reduced .010" less than the tunnel diameter.

Each rocker arm assembly contains a pair of arms attached to either end of a cylindrical sleeve that rotates on a rocker shaft. One arm pushes down on the valve in reaction to the other one being raised by a pushrod. The effective rocker arm ratios are not identical for the intake and exhaust valves. The ratio for the intakes is .841 and for the exhausts it is 1.08. The sleeve and its two arms are actually three separate parts coupled together by a circular array of dowel pins on either end of the sleeve. The pins were pressed into the ends of the sleeves, but the holes in the rocker arms were drilled and reamed one thousandth oversize for slip fits.

I machined the rocker arms from 7075 aluminum. This alloy has 30% more tensile strength than machinable brass (recommended in the drawings) and is about 15% harder for a little better wear resistance against the valve and pushrod ends. The arms were machined in two groups: four valve rockers and four pushrod rockers.

Those who have followed any of my previous builds might recognize the construction technique that I like to use when machining these kinds of parts. Each group of rockers was completely machined from the topside of its workpiece in cookie sheet fashion, and then the machined troughs around each individual part were filled with Devcon 5 minute epoxy. This glue held the parts in place while the workpiece was flipped over and faced to bring them to their final thickness. Heating the workpiece to 350F cleanly released the finished parts. In the past I've use a heat gun to warm the epoxy, but lately I've been putting the whole workpiece in an oven for half an hour or so. It's important to wear gloves and push the parts free from the workpiece while they're still hot. If allowed to cool, the Devcon will re-bond to the parts.

The sleeves between the rocker arms were turned from 6061 since strength and wear are less of a concern with these parts. A pair of radial oil holes drilled at either end of the sleeve and connected by a longitudinal distribution slot provides an oil film between the sleeve and shaft. This slot was also used to align the drilling of the circular hole arrays on the ends of each sleeve in order to align the rocker pairs. Spacers between the pushrod-end rocker arms and the rocker covers fill the remaining space on the rocker shafts.

The locations of the pushrod-side rockers with respect to the holes drilled for the pushrod tubes in the rocker covers were also verified. A snug-fitting dummy rod with a pointed tip was used to mark the ends of the rocker arms to transfer the centers of the pushrod tubes to the tips of the rockers. An oil hole was through-drilled and a hemispherical cavity was plunged into the tip of each rocker at this location.

When assembled, there was no discernible lash measured at the locations of the valves due to the clearances in the parts making up the rocker assemblies. - Terry


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## mayhugh1

Scratch-made model engine oil fittings are among my least favorite parts to work on. For what they do, they require an inordinate amount of work and use tiny little workpieces that continually go missing in my shop. Whenever possible, I cheat and adapt commercially available parts - usually 1/8" tube compression fittings that I find in auto parts stores. These can be a bit large for the scales involved, but they seem to look at home where I've used them. For this engine, though, I'll have to 'knuckle' under and fabricate them from scratch because there's just no room for commercial parts.

Inside the rocker boxes there's very little space for the soldered spray bars used to lubricate the rocker arm assemblies. They're tucked behind the rear-most rockers, and their soldering has to be very carefully done so that what little clearance is available isn't taken up by over-soldered joints. The edge of the circular mounting recess inside each rocker box also has to be chamfered to clear even the tiniest solder fillets on the rear of the assembly's copper nozzles.

The drawings specify 1/8" copper tubing for plumbing the entire oil system. The bottom end, including the cams and crankshaft, are splash lubricated by a wet sump. There is an oil pump, but it's only used to feed the spray bars in the engine's top end. If the gravity-fed oil returns in the valve boxes can't keep up with the pump, the boxes can fill with oil and flood the valve guides. If this happens, it may be necessary to reduce the oil flow to the top end. After the engine is completely assembled and running, a relatively painless way to do this will be to add a restrictor in the feed tube to the rocker boxes. Limiting oil to the top end might even reduce some of the leaks for which the full-scale version of this engine is famous.

An arbitrarily short restrictor in the feed line to the spray bars won't necessarily achieve the desired effect, though. In fact, a restrictor that's too short can increase the velocity of the flow without significantly reducing its volume - sort of like holding your thumb over the end of a garden hose. The flow Q of a liquid through a tube is given by:

Q = (pi)(dia^4)(P)/(u*L)

where P is the applied pressure, u is a viscosity constant, L is the length of the tube, and dia is its i.d.. This equation shows that the flow is proportional to the square of the area of the tube rather than just its area. This may explain why trying to control flow with a quarter-turn ball valve can sometimes be so frustrating. An important point, however, is that flow limited by a restriction will be dependent upon the length of the restriction.

Since I might later need to fractionally reduce the flow, and since absolute numbers are dependent upon a pesky viscosity constant, I can ratio the equations written for a restricted and an unrestricted case and eliminate the need to know the viscosity. For example, if I want to cut the flow in half by using 3/32" tubing (.063" i.d.) in the feed tube but continue to use 1/8" (.094" i.d.) for the rest of the tubing, then after a bit of math,

Qrestricted/Qunrestricted = 1/2 = (.063^4/.094^4)*(Lunrestricted/Lrestricted), or

Lunrestricted/Lrestricted = .5/.2 = 2.5

This means that if the unrestricted case happens to use a total of 14 inches of 1/8" tubing between the pump and the spray bar, I can cut the flow in half by replacing 4 inches of the 1/8" tubing with 3/32" tubing.

I really won't know if there's an issue until the engine is running, but if there is, I'll have a backup plan that won't require disassembling the entire engine. At this point my goal is to wrap up work on the heads, and this will now require some half dozen oil fittings. I started with the spray bars that lubricate the rocker arm assemblies. Each of these is simply a pair of copper nozzles soldered into a brass puck that fits into a recess in the rear wall of each rocker box. Reducing the diameter of the nozzles to 3/32" from the drawing's recommended 1/8" helped a bit with the clearance issues, but things are still pretty tight in that area.

A custom compression fitting that receives oil from the feed tube is next threaded into the spray bar through the rear of each rocker box. I basically followed the drawing for these fittings, but added a groove in their bases for a 1mm x 4.5 mm o-ring to seal them to the rocker boxes. Their machining was many hours of mind numbing work mixed with a lot of procrastination. I didn't bother taking photos since the steps themselves were trivial, and there were lots of them. All totaled, there were some two dozen individual manual lathe operations and half as many setups involved with making each three-piece fitting. The starting workpiece was a twelve inch 3/8" diameter brass rod, and all the operations were done on a manual lathe. The ferrules were machined with flat rear surfaces so I'll have the option of soldering them to the tubes before assembly. This will eliminate one of the two crush seals typically found in larger commercial fittings. I ran across this trick for improving the reliability of miniature tube fittings in a small scale live steam text.

The Knucklehead drawings actually show soldered-on threaded fittings for the tubes making up the returns from the valve boxes. I couldn't visualize an assembly/disassembly strategy associated with using them, and so I took what I thought was a safer approach and used compression fittings here also. I may find out later that this was a mistake because of space limitations. After working the kinks out of the processes for making each of the three parts, I made what I hope are enough to finish the entire engine plus a few spares. - Terry


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## johnmcc69

Great post. I like your thinking with the oiling system & especially the O-Rings.

 John


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## Buchanan

Terry.
 I am enjoying this build as much as all your others. 

 I was looking at the beautiful work in the heads and a thought passed through my mind. Just think how good a Knucklehead radial would look! You might need to rearrange the direction of the head fins though, and a few other details that I haven't thought of.  
I really like your work. 
Buchanan.


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## mayhugh1

The Knucklehead's port hardware consists of two pairs of stainless steel flanged tubes that will eventually mate with the intake manifold and exhaust pipes. The tubes themselves are close fits inside the holes that were bored into the areas behind the valves during the head's initial machining. They will be held in the heads with setscrews threaded through the bottoms of the heads. These screws won't be accessible after the heads are bolted to the cylinders, and so each flange is machined as a separate component that's captured to a tube in a two-piece assembly. Being separate will allow the flange to rotate on its tube so its bolt holes can be aligned with those on the flange(s) of the intake manifold or the exhaust pipes during final assembly. Adding this complication to the port-side flanges will allow simpler flanges to be used on the much higher risk intake and exhaust components later.

The parts were all machined from 303 stainless, and the flanges were each tapped for six 2-56 SHCS's. When tapping stainless or ferrous metals I use a dark brown moly pipe threading oil that I found in a hardware store some twenty years ago. This oil makes tapping operations in steels seem effortless, and I don't think I've broken even an 0-80 tap while using it. You have to clean the workpieces right after using it, though, or it will stain them and probably one's flesh as well. Portions of nearly all my tools have been patina'd by this stuff over time. Unfortunately, I've not found anything that works as well with aluminum. (I currently use lowly WD-40.)

The joints between the mating flanges will need to be sealed to prevent leakage. The original design recommends a .010" thick copper washer to do this, but I happened to have some -012 o-rings left over from previous projects that I used instead. During assembly, an o-ring will be compressed between the mating flanges and will seal the interface between them. The o-ring fills a machined groove that's equally divided between the two components of each port-side assembly, and so it will seal the gap between them as well.

Silicone has a temperature rating of nearly 500F which should be more than adequate to handle the temperature rise of the components heated by the exhaust gasses. I've recorded the header temperature measurements on the five multi-cylinder model engines I've built so far and have never seen temperatures greater than 350F. Silicone will dissolve in fuel, however, and so Viton o-rings will be used with the intake flanges. - Terry


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## ddmckee54

Terry:

You've got an O-ring sealing between the tube and its' flange and the fit between the tube and the head is a close fit.  What's going to be the seal between the head and the tube?  I know that you're good and it WILL be a close fit, but you're still going to get a vacuum/exhaust leak at that point won't you?

Don


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## mayhugh1

Don,
Those will be Loctited in place. Thanks for asking.
Terry


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## ddmckee54

Thanks Terry, that explains the need for the flange to rotate on the tube.

Don


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## mayhugh1

A parts list found in the download describes the Knucklehead's valve springs as having an o.d. of .375" and being wound with .035" stainless spring wire to a free length of .500". An included commercial part number adds to the specs a minimum compressed length of .230" and a 13.6 lb/inch spring rate.

In his own build, Steve mentioned that he ran into issues with spring bind. Based on his comment I deepened the valve boxes almost .10" over what was shown in the drawings when I machined them, and I shortened their mounting screw heads. This effectively increased the springs' installed height. I also shortened the guide portion of my valve cages which brought their tops down an additional .18" below the rocker arms in order to eliminate any possibility of interference with the upper spring cup. Since I had some .031" diameter stainless spring wire on hand, I decided to also wind my own springs.

After some experimenting, I came up with a .36" diameter spring having a .15" minimum compressed length using four turns of my wire wrapped around a .240" mandrel. A check of the spring rate showed a value similar to that in the Draw-Tech spec. In addition to using smaller wire, I was able to reduce the springs' compressed length a bit more by carefully forming and grinding their ends flat without adding any inactive turns. Flat ends can be beneficial for valve springs since they help keep the valves consistently centered on their seats especially if there is excessive clearance in the guides.

The finished springs were heat treated for 45 minutes at 400F. This partial annealing relieves internal stresses created by the winding process, and it improves the spring's ability to hold its free length and spring rate over time. After completing six springs I carefully measured their spring rates using a height gage and a small force gage that I snagged from eBay. The average was approximately 13 lb/inch which was very close to the original spec.

As mentioned earlier, the designs for the spring cups and valve guides were in the pdf that was missing from my download. Steve sent me a copy of the one he used since Draw-Tech may have pulled it from the download in order to look into the binding issue. I machined the cups from phosphor bronze while making minor modifications to them in order to reduce their contributions to the spring stack-up. This included changing the valve retainer on the top cup from a pin to a 'U' clip which increased the spring's installed height slightly.

In a low-revving model engine the valve springs need to be strong enough to keep the closed valves tight on their seats especially during starting. While leak-checking valves during my previous engine builds, I concluded that 1 to 1-1/2 pounds of force on the face of the valve under test was sufficient to obtain consistent leak-down times on usable valve/seat combinations. With a spring rate of 13 lb/inch, my scratch-wound springs will create just over 2 pounds of force at their installed height which results from .15" of compression. With a simple test fixture using one of the scrap valve cages machined earlier from some questionable bronze, I measured the maximum available valve travel to be .165".

The cam drawing shows the exhaust valves' lobe heights to be .065", and since their rocker arm ratios are 1.08, the expected exhaust valve lift will be .070". Similarly, the expected intake valve lift will be .060" x .841 = .050". The exhaust valve lift will create a worst-case pushrod load of just under 3 pounds. With this 3 pounds I'd be a bit more concerned about wear if the engine wasn't using a roller cam. Even so, I'm certain I have some .026" wire stashed away somewhere in my shop, and I may re-visit the springs if I can find it.

To prepare for machining and leak-checking the valves, I permanently installed the port hardware. Since my leak test will involve pulling a vacuum behind each valve while installed on its seat, the o.d.'s of the port tubes need to be sealed to the heads. For this I used 620 (high temperature) Loctite. Draw-Tech's design includes 6-32 setscrews threaded through the bottoms of the heads to secure the tubes. I ground points on these setscrews before installing them so they would bite into the tubes for a little more security. Both the intake and exhaust tubes will eventually be expected to carry some cantilevered weight while the engine is shaking on its mounts. - Terry


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## doc1955

Been following along I'm actually been planning on building this one. You are doing some might fine work looks nice!! 
 I did start modeling things up I want to get a model completed before diving into it. I hope to start building this fall here is what I have so far. I've only been putting things together model wise when I have spare time. The drawing of the heads was somewhat confusing but I see you did a nice job on them with the info you had NICE!

My model so far.
its a 3d pdf file.


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## stragenmitsuko

Lovely , another build by Terry . :thumbup:

Pat


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## mayhugh1

doc1955 said:


> Been following along I'm actually been planning on building this one. You are doing some might fine work looks nice!!
> I did start modeling things up I want to get a model completed before diving into it. I hope to start building this fall here is what I have so far. I've only been putting things together model wise when I have spare time. The drawing of the heads was somewhat confusing but I see you did a nice job on them with the info you had NICE!
> 
> My model so far.
> its a 3d pdf file.


Doc,
I can't seem to bring up your pdf. My Windows PC's may be too old, but I thought my new Mac laptop wouldn't have an issue. Terry


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## doc1955

You have t down load then open with adobe.


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## mayhugh1

The Knucklehead's valves were machined from 303 stainless. Compared with those in other multi-cylinder engines I've built, these valves are huge at .625" diameter. Earlier when I machined the valve cages, though, I reduced them to .570" so the edges of the combustion chambers would have a bit more safety stock.

When I was making valves by the dozens for my radials, I learned to machine them in one large lot that I shepherded through six machining operations. Before jumping into production, however, I completed at least one valve that I trial fitted into all the cylinders so I could check for machining inconsistencies. There's often a number of machining operations that can affect the requirement for a valve's length, and some of these can be hard to control. Although it may sound risky to put off lapping and testing until after all the valves are machined, I probably saved a lot of time and avoided errors by not changing and recalibrating the set-ups for each and every valve.

The first operation is to create the starting workpieces. For the Knucklehead this involved sawing a 5/8" diameter 303 rod into short lengths so a complete valve could be machined on either end of a central one inch work-holding spigot.

The second operation involves roughing out the valves on both ends of all the workpieces. This is my favorite step because I can turn my little Wabeco CNC lathe loose with very little handholding. I typically use a CCMT 21.51 roughing insert or sometimes even a dull finishing insert that's been retired from service. Surface finish isn't yet important because this step leaves a diametrical excess of .020" stock. A tailstock isn't bothered with since stem taper will be dealt with later. However, before starting the operation the ends of the workpieces are center drilled to prepare for the next step.

The next step is the finishing operation, and it uses a very sharp DCMT 21.51 insert typically intended for aluminum. Three passes are used to remove the remaining stock except for the last 1 to 1-1/2 thousandths. Either the tailstock is used for this operation, or I will back up the free end of the workpiece with a piece of leather held in my right hand. (I realize this sounds wonky, but after a little practice it actually works pretty well.) The speed and feed are adjusted for the best possible surface finish. During this step my lathe requires some hand-holding. Upon completion of each valve, its stem diameter is measured, and the lathe's work offset is corrected as needed before taking on the next valve.

The valve stems are brought to their finished length in a fourth (lathe) operation. The workpiece is inserted through the rear end of a 5C collet so the valve to be trimmed can be gripped close to the end of its stem. The groove for the retainer clip is also cut in this step.

In the fifth step the workpiece is re-chucked on its spigot so the last thousandth or so can be polished from the valve stems. I start with 400 grit paper if I have more than a thousandth to remove. The last thousandth is removed with 600 grit paper, and the stem is mic'd along its length during the process. When finished, a dab of white buffing compound on a rolled-up paper towel moved along the entire spinning valve brilliantly colors it.

In the last operation, the two valves are sawed free of the spigot which is gripped in a vise attached to my bandsaw. With some care, the larger diameter spigot prevents the polished valves from being marred. The stem of each freed valve is then gripped in a 5C collet up close to the valve head so its face can be finished in the lathe. Again, light passes with a sharp finishing insert produce a nice surface finish without deforming the completed valve.

Before starting my little production run, I used a test valve to search for an optimum stem length for both the intake and exhaust valves in both heads. The length I was looking for was one that would rotate the pushrod rockers perpendicular to their pushrods with the rocker arms resting on their closed valves. Somewhere between the valve and pushrod drilling operations, though, one of my compound angled setups must have been off. As a result, two valve lengths will be needed - one for the valves in the left side of the rocker boxes and another for the valves in the right side of the boxes.

The need for two valve lengths created another issue. Measurements using my previously finished springs showed the pushrod forces now approaching four pounds in the valve trains with the short valves. I had already been uneasy about these relatively high forces when all the valves were the same length and longer. As a result, I decided to make a new set of valve springs.

I machined the two different length valves in a mini production run. I also machined a lap which was nothing more than a completed and polished valve that wasn't parted off from its spigot.

Unlike what I've done on full-size engines, I like to finish model engine valve seats with a separate lap rather than lapping them to their mating valves. After all, the valves come off the lathe with correct and concentric geometry, and they're brilliantly polished as well. The seats also have the correct geometry, and they're concentric with their guides thanks to the piloted seat cutter used to cut them. Their sealing surfaces, though, have marks left on them by the seat cutter that, at the scale of a model engine, can create leaks.

Over time I've 'honed' a technique that helps to minimize the marks left by the piloted seat cutters I use. I coat their teeth with cutting oil and their pilot with motor oil. The oil reduces the chatter that can sometimes be felt while turning the cutter. I'm also careful to apply only a minimum force to the cutter. Pushing too hard can gouge the seat requiring it to be made wider than necessary. I usually orient the head so the cutter is vertical and allow its own weight to do the cutting. I try to keep the final seat width on the order of .005" in order to minimize the amount of material that will have to be removed to clean up the marks.

Lapping can damage a perfectly good valve especially if the marks on the seat are prominent. I feel these marks are best removed using a sacrificial lap and a very fine lapping compound such as Timesaver. The whole process takes less than ten minutes including the time used for leak testing along the way. I perform my leak-checks by pulling a vacuum in the port behind the closed valve under test using a Mity-Vac. My own subjective goal is to achieve a 25 to 15 inHg leak-down time of ten seconds or more. This is probably overkill but it's not difficult to achieve when the seats have the proper starting geometry. This check can also take leaky valves off the table as a potential problem when trying to start an engine for the first time. If valve cages are used, their geometry can be verified with a very light pass of the seat cutter before the cage is installed in the head.

After leak-testing the valves, I turned my attention back to the valve springs. I wound a new set of springs on the mandrel used for the first set, but this time I used .026" diameter spring wire. I ended up with approximately the same i.d., o.d., and length but with one less turn. The finished springs had a measured spring rate of 5 lb/inch which reduced the worst-case pushrod loads to a bit more reasonable 2.3 lbs.

This finally completes the work on the heads. I'll likely move on to the cylinders next as I work my way down from the top of the engine. - Terry


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## mayhugh1

The cylinder design has good looking proportions and cosmetic detail that requires some effort and care to machine. The finished cylinders will look similar to those on the full-size engine except for the radial notches for the head fasteners.

I had some 12L14 stock left over from my radial builds that was ideal for the workpieces. After band sawing them to length, each was chucked in my Enco lathe so their ends could be faced and center drilled. Their centers were drilled out in three separate steps and then bored to within a thousandth or so of their final value in order to reduce the amount of honing that will be required later. A heavy bar with a sharp insert was used to obtain the best possible surface finish. I also skimmed a short length of each workpiece's o.d. so I'd have an indicating surface for later use.

The cylinders' machining operations require full access to the outsides of their workpieces, and so I prepared an expanding mandrel to support them by their i.d.'s. The 5C machinable mandrel used for the Merlin's liners needed only a bit of material removed from it in order to fit these new workpieces. After turning its o.d., the mandrel was left captive in my Wabeco's collet chuck until all the cylinder lathe work was completed. I loaded and indicated the workpieces on the mandrel a couple times while checking their TIR's. They were consistent to within a half thousandth even though the cylinders' machining wouldn't require such accuracy. Mainly, I was curious about the mandrel's consistency.

The cylinder drawings specify through-hole clearances for 10-24 mounting studs for securing the cylinders to the engine's (split) crankcase. In the original design, even small pattern nuts would have overhung the cylinders' mounting flanges and bugged me to no end. Enlarging the flanges might have opened up a can of worms that infected the crankcase, and so I changed the clearances to use 8-32's instead. Even then, I had to move their locations inward a bit in order to keep the even smaller nuts within the edges of the cylinders' mounting flanges.

The remaining lathe work began at the bottoms of the workpieces which will become the cylinders' simple ends. The material to be removed above their mounting flanges was essentially a deep wide groove for which I used the bifurcated grooving insert created a couple years ago to turn the rod bearings on my Merlin's crankshaft. This grooving operation had to be performed on my Enco lathe since the Wabeco doesn't have the rigidity nor the low speed torque to handle an eighth inch wide insert in steel. After machining the workpieces above and below their mounting flanges, they were moved to the mill where the perimeters of the flanges were milled square and their mounting holes drilled.

The hole patterns for the head mounting fasteners on the tops of the cylinders need to be accurately oriented with the flange mounting holes on the bottoms of the cylinders. If not, among other consequences, the intake manifold will become even more difficult to fabricate than it's already going to be. The cylinders' mounting flanges were clamped in the mill vise for alignment of the workpieces to the mill so the clearance holes for the head studs could be properly located and drilled.

The cooling fins have cosmetic detail that requires extra effort to machine, but the final results are well worth the effort. The edges of the fins and the valleys between them are fully radius'd. Since I had machined similar fins on the cylinders of my last radial, I resurrected the CAM software and tooling that I developed for them. I ran into some issues back then, though, that I now had to revisit.

The first problem is that the mandrel'd steel workpiece has significant unsupported stick-out and at 1300 rpm can only marginally handle a .040" wide radius'd insert without raising chatter resonances between it and the lathe's lightweight cross feed. As a result the machining needs to be done in a series of brief pecks. This also means that the thin fragile insert also has to handle a side-to-side clean up pass to remove scallops left by the pecking. The insert I'm using isn't really designed to do this.

Another issue is that the CAM (Sprutcam 7) software that I'm using doesn't seem to have the flexibility to peck-turn arbitrarily shaped workpieces. It has a grooving operation, but it doesn't seem to know how to distribute the pecks within the workpiece when the workpiece is something other an ordinary cylinder. Used per its manual, the software tends to generate g-code that causes the tool to spend most of its time pecking air outside the complex contours of my roughed-in cylinders. In order to get it to behave, I found that I had to describe its job assignment as I would if I were milling the part rather than turning it. The turning operations usually know how to deal with turning assignments, but they have to be coaxed (or tricked) into working with milling assignments. After spending countless hours playing with things that shouldn't matter (every part seems to be a special case), I finally came up with usable code. Those hours spent getting usable code were well worth the effort back when the goal was to machine 20 identical cylinders. For these two cylinders, however, a form tool would have been more efficient although less satisfying.

To make things a little more interesting, the Knucklehead's radius'd grooves were also a bit deeper than those for which the insert and its holder were previously modified and used. Another .030" had to be removed from them both in order to obtain the clearances needed for the deepest grooves. Most likely this didn't help with the chatter, and I was very lucky the weakened insert didn't fail during the finishing operations. 

Two more operations remain before the cylinders can be finally honed and blued. -Terry


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## e.picler

Congratulation Terry!
Very nice quality work. This engine will be a "Piece of Art"

I'm learning a lot about machining following your building.

Thanks,

Edi


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## MacKendrick

How do I view the pictures?


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## Cogsy

MacKendrick said:


> How do I view the pictures?


 
They should show up in the thread for you. If they're not, log in to your account settings at the top of the page and click on 'edit forum options', then look for the check box for 'show images' and make sure it's checked.


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## mayhugh1

For me, the trickiest machining operation on the cylinders turned out to be cutting the radial notches which will eventually be used to access the nuts on the head studs. Before giving it much thought, I figured I'd machine them using a custom ground cutter on the end of a boring bar. When time came to do it, I realized the bar's diameter would have to be impractically small in order to have any clearance between it and the cylinder's o.d. during the operation. So, I looked into using a modified Woodruff cutter instead.

As the drawing below shows, the Woodruff cutter has pretty much the same problem. The notches have to be deep enough so the nuts, with a bit of clearance around them, can sit flat on their mounting surface which will be the underside of the second upper fin. Using small pattern 8-32 nuts, the 7/8" diameter circular notch called out in the cylinder drawing will work although with little to no margin. The diameter of the cutter's shank, which must be small enough to clear the adjacent fins, is still the issue.

I had a 7/8" diameter HSS Woodruff cutter that I modified by turning down a portion of its shank. I used a triangular diamond insert that I scored off eBay many years ago but until now had no use for. Because of some limitations created by the shape of the insert, its tool holder, and the small working envelope, I had to turn down more of the shank's length than I wanted. (A tool post grinder was really needed here.) In any event, even though I needed the shank to be 3/32" in diameter, I gave up when I reached 3/16" since the cutter already looked too fragile to be usable in steel. This 3/16" cutter is in fact the one modeled in the below drawing, and it clearly shows there's still interference with the cylinder's o.d..

Since Steve had successfully cut these notches during his build, I emailed him to ask how he had done it. He replied with a photo of his Woodruff cutter with its ground down shank. Even though he had managed to make his cutter work, I wasn't at all confident in my ability to do the same with mine.

I considered using a larger diameter cutter with a correspondingly larger diameter shank. Modeling showed, however, that in order to get inside my comfort zone the notches would wind up wide enough to compromise the appearance of the cylinders.

I eventually decided to vertically mill the notches including their circular shapes since this would totally eliminate the clearance issue. Vertical milling would also allow me to reduce their widths and perhaps even improve the cylinders' appearance a bit. The notches really need only be wide enough to provide wrench access for turning the nuts 30 degrees, or so, at a time. I was able to check this before they were machined by printing out their design in full-scale on paper so I could lay an actual wrench and nut on top of them.
The notches were roughed out with an 1/8" carbide ball mill, and then finished with a 3/32" carbide ball mill. The minimum diameter of the finishing tool was limited by the availability of a cutter with enough flute length to handle the notches' full depths. The finishing cutter would leave a .047" radius fillet on the nuts' mounting surface, and so the notches had to be deepened by this same amount. Fortunately, there was enough material between the rear of the notches and the cylinder's bore to allow this. 

Roughing operations are typically performed with a cylindrical end mill, but in this case a cylindrical cutter would have left unsightly grooves in the filleted areas that the finishing pass wouldn't have been able to clean up.

The cylinders were returned to the 5C mandrel that was then chucked into a horizontal rotary under the Tormach's spindle. The plan was to automatically index the cylinders so all five notches could be machined in one extended operation. The indexing had to be done manually, though, due to some Sprutcam glitches with the job assignments that weren't worth solving nor going into. Because I wanted the notches to have an extra fine surface finish throughout, the total machining at 5000 rpm and 3 ipm wound up being a ridiculous 45 minutes per notch.

A feature that wasn't part of the cylinder's original design, but which I added, was a short taper on the i.d. of the cylinder's skirt. Its purpose is to gradually compress the piston rings as the pistons are being inserted into the cylinders during final assembly. This simple feature helps remove those nagging doubts about broken rings that can otherwise accompany the struggle often required to get them inside the cylinders.

Up until now, the cylinders have been identically machined. Their last operation makes them different and defines which cylinder will be the front cylinder and which will be the rear. This milling operation creates a clearance flat on the bottom of each cylinder's skirt so the two cylinders can be adjacently mounted to the crankcase with a 45 degree angle between them and allow the bottom edges of their mounting flanges to be nearly coincident. The skirt taper that I added earlier morphed the flats into small crescents. - Terry


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## petertha

Very nice. Those parts have quite a few complex features.

Re the skirt chamfer to assist piston ring compression, I think I put about .030" x 45-deg on my prototype liner. But I have extra material to work with that will never come close to the business end of the piston. Do you think a shallower angle & more gradual ramp is better yet, or basically just don't leave it square?

I probably asked you this before, but on your other engines 12L14 liners/cylinders, are you storing them with something like after-run oil? (ie. then drain before running). I keep 2 cylinder blanks in my spares box, one dry & the other in a baggy which is oiled. The non-oil one has some tiny rusty blemishes happening & Calgary is a pretty dry place. I suspect I'm going to end up going with CI liners for other reasons but you seem to be happy with 12L14. Maybe my case was differently sourced bar, they actually seemed to machine a bit different too.


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## mayhugh1

Peter,
I use a more shallow taper, but anything is probably better than nothing. I just cut them by eye and on these they came out .160" long and about 10 degrees or so.

Unfortunately, I haven't been as concerned as I probabably should be about storage. I've really not been doing anything special. - Terry


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## mayhugh1

Before having the cylinders hot blue'd, their bores were lapped to a common diameter with an extra fine surface finish for use with cast iron piston rings. Since I can machine the pistons and rings to any size I need, the bores' exact diameter isn't important at this point. Bringing them both to the same diameter, though, is important (especially with a large number of parts) and will simplify the machining of the rings later on.

I've been using commercially available laps with interchangeable brass barrels to finish the bores in my cylinders. I've tried to make brush hones and automotive brake cylinder hones work but always had disappointing results when trying to remove more than a few tenths of material. Barrel laps, on the other hand, are well-behaved even while removing a couple thousandths. I usually hold the part being lapped in one hand and a battery-powered drill spinning the lap at 200-300 rpm in the other.

I like to use a separate barrel for each of the three grits of Clover (Loctite) grinding compound that I typically use: 180g, 600g, and 1000g. The 180g paste is used to bring the cylinders to within several tenths of one another, and then they're finished to within a tenth using the 600g grease. That tenth, although not always repeatable, is about the resolution of my measurements. The final surface finish is usually laid down with the 1000g oil. Progress is continually monitored on each cylinder by measuring and recording the diameter of its bore at three different depths after each two-to-three minute lapping session. The critical portion of the bore is its upper half and is where I try to obtain a zero taper. The taper is slowly worked out by spending more time in the tighter portions of the bores. In order to improve my chances of efficiently creating an identical set of cylinders, I lap them as a group and remove only small amounts of material from each one at a time so they are all finished together.

When I carefully checked the cylinders' initial dimensions with a dial bore gage, I found their starting bores to already be within a half thousandth of one another. Although not a typical starting point for me, it was a nice place to begin. I was able to skip the 180g step and, using 600g grease, brought the bores to within a tenth of one another with no measurable taper. Since I would have had to turn a second barrel in my collection down to a unique diameter for the 1000g step, I decided instead to finish the bores with 800g and to just re-use the 600g lap. When completed, the bores had a nice uniform frosty gray appearance. The cylinders were then delivered to a local gunsmith for a quick turnaround passivation treatment that left them with an essentially zero thickness black oxide coating that will protect them from corrosion.

With the cylinders completed, I turned my attention to their gaskets. The head gaskets and cylinder flange gaskets were cut from .010" and .015" thick teflon sheet, respectively. Although the drawings specify the use of copper sheet, I wasn't sure the 8-32 studs in the soft shallow aluminum heads would be up to the task of setting a copper head gasket. Besides, I'd been looking for an excuse to experiment with Teflon gaskets after reading Steve Hucks' positive comments about his experiences with them.

I used a drag knife sold by Tomach to cut out the gaskets using my mill. With thin un-backed materials such as this sheeting, I've found it best to manually follow the blade around with a small hold-down tool to keep the material flat against the cutting table. The teflon parts tended to lift as they were cut, and since I was making two cutting passes, my little 'presser foot' helped produce a clean result especially on the narrow portions of the flange gaskets.

I thought I'd get this post in before the forum's software change this evening. Hopefully, my old XP computers will remain compatible with the site through that change. Unfortunately, I've never been able to post more than one photo from my Apple tablets even when using the available app.

I've been looking forward to working on the Knucklehead's crankcase since starting this project. Logically, it's probably the next step in this build. - Terry


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## petertha

Very nice machining. And the blue-ing came out very nice, looks awesome.

Re the gasket material hold-down, I use spray adhesive a lot for what might be similar conditions. Like paper CAD templates on wood, carbon, thin metal etc. It srobust enough to withstand scroll saw cutting, drilling, sanding etc. After I just spritz it with thinner or acetone & paper comes right off. I suspect the Teflon would be impervious to both. I also use spray glue it to make all kinds of abrasive sticks from wet-dry paper & whatever substrate works best, typically smooth MDF or small blocks of aluminum.

Just get the general purpose stuff typically for paper & cardboard, its typically fine mist & releases with solvent. 
https://www.homedepot.com/p/3M-16-75-oz-Super-77-Multi-Purpose-Spray-Adhesive-77-24/100067550
You don't want the high strength or specialized stuff, it comes out like silly string


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## mayhugh1

Peter,
Thanks for the tip. I never thought about the spray adhesive. I think I even have some that I use to repair a door panel in my wife's car. - Terry


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## doc1955

Those are really nice looking cylinders very nice!


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## mayhugh1

Doc,
Thanks. I still haven't been able to view your pdfs. I get the error message:

*Access to doc-08-b8-docs.googleusercontent.com was denied*
You don't have authorization to view this page.

403

whenever I click on the link you supplied. Perhaps you need to make some preference changes?
Terry


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## mayhugh1

The Knucklehead's case is made up of two separately enclosed sections. The first is a split crankcase whose left and right halves enclose the crankshaft and connecting rods. The second section, the cam box, bolts up against the crankcase and contains the oil pump, the camshafts, and all the gearing and belting associated with the distributor and (heaven forbid) electric starter. (Harley purists will likely consider an electric starter on a Knucklehead as blasphemy, but I've enjoyed the starter on my Merlin so much that I'm going to try my best to include one on any future engines that I build.)

I began work on the crankcase by entering its two piece design into SolidWorks but ran into difficulty while trying to get an exact match between the two halves. I had hoped to be machining the crankcase by now, but I ended up spending most of the week with SolidWorks. I've been finding an occasional dimension or two missing from some of the more complex drawings. When left/right-handed parts were involved, I've typically been able to appropriate the missing dimension from the drawing of its opposite handed part. This didn't seem to work with the crankcase drawings whose halves weren't identically dimensioned. When I thought I was done, I found the angle between the cylinder decks was 135 degrees on one of the crankcase halves and 134 degrees on the other. The printed drawings seemed correct because they matched up perfectly over a light table. I wasn't able to resolve which dimension(s) were creating the problem, and so I ended up overlaying my mismatched virtual halves in a SolidWorks assembly to fill in the differences.

The counterbores for the SHCS's that secure the two crankcase halves together will break through the fillets on the outer edges of the left-half crankcase. To eliminate this, after finally having a matching crankcase pair, I increased the entire outer perimeter of the crankcase by 1/8". The extra real-estate allowed me to add a groove for some 1/16" o-ring cord stock to seal the two halves together. Since I plan to add two more o-rings with rather complex contours to the case, I wanted to make sure they stay in place inside their grooves so they don't become a nuisance during assembly. I made some tests by cutting a couple trial grooves for this first o-ring in a piece of scrap. A .070" wide by .055" deep groove nicely retained the o-ring, provided .015" compression, but had a 99% fill that didn't provide any room for temperature expansion. A .075" wide by .055" deep groove didn't retain the o-ring quite as well but had only a 93% fill. After some more procrastination I'll probably select .073".

When I enlarged the periphery of the crankcase, I also raised the cylinder decks above the crankshaft by the same 1/8" in order to preserve the model's original appearance. I thought I'd better take a look at the engine's compression ratio since I didn't yet know what the original design intent was, and my increase in cylinder deck height was going to reduce it. A calculation that included an accounting for the volumes of the valve heads inside the combustion chambers showed the static c.r. was approximately 5.5 before my change and an anemic 4.1 afterward. A well constructed multi-cylinder model engine will happily run with a compression ratio of 5.5, but 4.1 begins to reduce its chances of starting. All my multi-cylinder model engine experience has been with c.r.'s closer to seven.

In the original design the outside top edges of the mildly domed pistons are already coincident with the bottom edges of the combustion chambers at TDC. The huge hemispherical combustion chambers will require higher domed pistons and maybe even 'eye-brows' cut into the valves if the c.r. is to approach seven with the engine remaining interference-free. A change of this magnitude will require some careful thought and modeling later on, but for now it's clear that I'll at least be adding that same 1/8" to the lengths of the connecting rods.

During the modeling I discovered a potential interference between the lower fins on the cylinders and the outer oil lines that return top-end oil from the valve boxes to the crankcase. In order to sidestep some heroic bends in the oil lines later on, I relocated the holes for the two associated fittings in the top of the crankcase to the extreme outside corners of the cylinder decks. This modification won't come for free as it will affect access to the nuts on the nearby cylinder mounting studs. Notching the cylinders would have been another option, but mine were already completed.

There's a circular array of five 8-32 drilled/tapped holes in the right half of the crankcase that will be used for attaching the cam box. I moved the hole located at the 12:00 o'clock position downward a bit because the head of the screw in this hole inside the cam box will block an oil return to the cam box. The oil sump is shared between the crankcase and the cam box through a pair of interconnecting holes at the bottoms of each section. I didn't notice an easy way to drain the oil, so I added a drilled/tapped hole in the bottom of the crankcase for a drain plug.

Another modification that I made was to increase the radius of the circular notch on the tail of the crankcase for clearance to the starter motor. The cut-out was originally designed around a 540 size motor, but I increased its diameter so I would have the option of adding a cosmetic cover around a 540 motor or using an even larger motor if necessary. Finally, I added holes for a pair of dowel pins to positively locate the two crankcase halves together as well as for use during machining. Finally, a second o-ring groove was added to the outside of the right half crankcase for a positive seal to the cam box.

Although some SolidWorks time is still needed on the cam box, I think it's safe to start making chips on the crankcase.

The modifications that I've made and will probably continue to make are in no way intended to be a criticism of DrawTech's excellent work. I find it extraordinary, without building a prototype to de-bug its design, that there aren't a number of major issues with such a complicated project. It's always much easier to make modifications to someone else's work that it is to create one's own original project. I certainly couldn't have come up with anything like this engine on my own. I suspect that many others would also like to build this engine but are hesitant because its design hasn't yet been popularized by a number of running examples on YouTube. Hopefully, those following this build will view it as a validation of DrawTech's design rather than any sort of criticism. - Terry


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## mayhugh1

The Knucklehead's case will require machining three relatively large chunks of aluminum most of which, depending upon the work-holding margins, will be returned to the recycler. I spent an inordinate amount of time trying to come up with a machining sequence that wouldn't require a lot of special fixtures but would guarantee the required alignments among the finished parts. I'm sure there are better ways to go about machining these parts without generating as much waste as I did, but my tired brain eventually had enough and began pleading with me to start making chips.

All three parts will end up with final shapes that will make their work-holding a bit sketchy especially during the heavy cuts involved with pocketing their voluminous interiors. The cam box, in addition, will require a number of precise boring operations to locate its various bearings, gears, and shafts. My plan included performing as much of their machining as possible while the workpieces still had straight sides and could be easily held in a vise.

For cosmetic reasons the complex peripheries of the final parts, especially the crankcase halves, should wind up closely matched to each other. Because of a very tall workpiece stack-up, it would make sense to machine the two halves in separate setups and then file and sand away their differences after assembly. My tentative plan, though, is to temporarily assemble the two halves and machine most of their exteriors in a single operation - mainly to see if I can. With a large enough diameter cutter this wouldn't be a big deal, but a spindly 3/8" diameter end mill with 2-1/2" long flutes will be needed to reach all the crankcase's outer features. My current work-holding strategy will handle either approach but, before finally deciding, some experiments will be done to check the effects of tool chatter and deflection.

Back in the shop, my first steps involved truing up the long sides and both faces of three 1-1/2" thick chunks of aluminum. These roughly 6" x 7" blocks came out of a couple weathered fixture plates acquired from a salvage yard many years ago. Taken two at a time, they were bolted together using a temporary 1/4" bolt through their approximate centers so the holes for a pair of dowel pins as well as the SHCS's that will eventually hold the finished parts together could be drilled through them. Deep drilling parabolic drills were used as pilots for the dowel holes before they were reamed. Prior to installation, an end of each dowel was center-drilled with a tiny divot so its center could be precisely indicated under a spindle microscope.

Remarkably, the y-axis differences in the dowel hole exits on the opposite sides of the workpieces measured less than a half thousandth, and the distances between them varied only a few tenths more. If the holes actually aren't straight, then they're off by the same amount. With the dowel hole pairs being so closely aligned with the fixed jaw of the mill vise, corrections for workpiece rotation won't be necessary after all. The workpieces were all marked so they can be consistently returned to the fixed jaw of the vise for additional machining.

The dowel pins in each workpiece lie on the x-axis centerline of the crankshaft. Its y-axis centerline is centered between the crankcase dowels but had to be offset from the center of the cam box dowels. Later on, the three blocks will be temporarily assembled, and a crankshaft center hole will be bored through the temporary center holes in the entire stack.

As mentioned earlier, it was important that the long sides of each pair of workpieces be parallel to the fixed jaw of the mill vise during the dowel hole drilling even though their widths were unequal. To achieve this, the bottom workpiece in the two-piece stack was clamped in the vise while the top workpiece, after being traversed with a dial indicator, was clamped to the bottom workpiece using the temporary center bolt. Unfortunately, I found that the 1/4" bolt, even with a large beveled washer under its head, couldn't supply enough clamping force to keep the two in perfect alignment even after a light tap from a plastic mallet. This issue arose because the workpiece's 'flat' surfaces actually ended up convex by a couple tenths, and there just wasn't enough contact area around the bolt. I was concerned that the top workpiece might rotate out of alignment during drilling, and so I augmented the bolt with a bead of JB Weld along the rear edges of the parts' excess stock. In retrospect, a sheet of paper between the two might have cured the problem so I wouldn't have had to put up with the overnight epoxy cures. This pairing and drilling procedure was performed on the workpieces for the left/right crankcase pair and then repeated for the right crankcase/cam box pair.

The next step was to pocket the interiors of the three workpieces after indicating their dowels or dowel holes. All three parts were pocketed, and the o-ring grooves were machined on the two workpieces with already finished surfaces. The o-ring groove on the outside of the right half crankcase will be machined later after its surface is finished. At this point its surface contains some excess stock since it might be used later as a machining fixture for the cam box periphery.

The pocketing of the crankcase halves was uneventful, but things got pretty exciting inside the cam box. For the pocketing operations I used a 3/8" three flute HSS steel corncob rougher followed by a 3/8" carbide four flute finishing tool. I ended up destroying two roughing end mills while machining the bottom of the pocket inside the cam box's workpiece. I could tell from the sound that abruptly started that the first cutter had suddenly and dramatically become dull, and so I quickly paused the Tormach before damaging the workpiece. A brand new replacement cutter lasted only a minute or so before it too began making the same noise. This time, however, before I could halt the machine the cutter jammed against an inside wall of the pocket and broke off. Inspection of the broken end showed it had dulled exactly like the first cutter. The depth of cut was only .150", plenty of coolant was being used, and there was no sign of aluminum welding - just a badly worn tip. I eventually had to conclude that the cutter's long stick-out combined with the unsupported 1/8" thick floor of the cam box probably triggered a resonance that, once started, quickly took out the cutter. Since the roughing pass had left plenty of excess stock for the finishing pass, the finishing tool nicely cleaned up the pocket except for a gouge on a top inside corner that occurred when the cutter broke. The gouge didn't extend into the o-ring groove and will be hidden by the cam box cover, and so I'm trying to ignore it.

All three workpieces were then temporarily assembled, and the reference hole for the crankshaft was bored through the entire stack. This hole, by itself, will be sufficient to indicate the locations of the counterbores for the bearings and seals inside the crankcase. The various shafts, bearings, timing pulleys, and gears inside the cam box, though, will also require the the dowel pins as references.































The next steps should include the machining of the cam box cover as well as the crankcase and cam box peripheries. - Terry


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## mayhugh1

More photos:[/ATTACH]


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## doc1955

You have done some of the things I've done but I'm only in the modeling faze I don't plan on starting the build until late this year. Some of the modeling of things has been a challenge ( heads especially) but I'm about 3/4 done with the engine model . 
Once I get the model done I plan on doing  my own set of drawings. You have gotten things looking pretty nice!!


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## byawor

I cut my slots on EDM sinker. This is a scrap barrel just trying the process.
Bob


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## mayhugh1

byawor said:


> I cut my slots on EDM sinker. This is a scrap barrel just trying the process.
> Bob


Bob,
That's pretty novel and would never have occurred to me. I'm curious about the surface finish, though. Could you take a head-on closeup photo of one of your better test slots?
Thanks,
Terry


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## stragenmitsuko

Just wondering , 

I'm an acceptable machinist . 
Not the worlds best , but I do have 30 years of experiance give or take . 
What I don't have , nor have acces to is cnc equippement . 

What I have is a lathe , a  mill with  rotary table and  dividing head and a clarckson t&c grinder . 
I have acces to a surface grinder . All machines are industrial grade . 
I can also do castings in ali and tig weld in ali and stainless . 

Can a build such as this beautifull knucklehead be done with conventional machining only ? 

Pat


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## mayhugh1

stragenmitsuko said:


> Just wondering ,
> 
> I'm an acceptable machinist .
> Not the worlds best , but I do have 30 years of experiance give or take .
> What I don't have , nor have acces to is cnc equippement .
> 
> What I have is a lathe , a  mill with  rotary table and  dividing head and a clarckson t&c grinder .
> I have acces to a surface grinder . All machines are industrial grade .
> I can also do castings in ali and tig weld in ali and stainless .
> 
> Can a build such as this beautifull knucklehead be done with conventional machining only ?
> 
> Pat


Pat,
I think the answer is yes. Steve did it here:
https://www.homemodelenginemachinist.com/threads/stephens-knuckle-head-build.24705/

Terry


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## byawor

Just a note of caution. I'm no expert. The sinker was left over when we sold the big shop years ago. I kept it as there really is no value to the machine. Unfortunately the guy that used to run it passed away a few months ago so I am pretty much on my own.  There is a direct relation between surface finish and rate of metal removal. since I am not very patient I had the machine cranked to max so the surface finish is not good sort of like  sand blast. I think the way around this is to make two electrodes a slightly smaller one for roughing and then one to size, run at much lower settings to improve finish. Also I used copper which wears very fast so I am making a graphite electrode see how that works.
Bob


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## AdvenJack

Friends, I wonder if the opening poster and others, who are able to create such wonderful examples
as what we see coming together here, can imagine how a know-nothing like myself admires your skill.
I tip my hat to you who are doing these projects. Keep up the inspiring work!!!


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## byawor

*here is a picture of the slot cut with edm. Looks worse in the picture and might be able to improve at a finer setting but  it would take forever. There has to be a better way!
Bob*


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## mayhugh1

The perimeters of the cam box and its cover will be machined together at the same time. The cover's inside surface will eventually be pocketed for several bearings that will need to be bored in alignment with their counterparts inside the cam box. The exact locations of some of these aren't yet known because they'll depend upon the gear reduction requirements of the starter motor which hasn't yet been selected. After the peripheries are machined, a rectangular fixture plate will be used to locate and machine the bores in both the cam box and its cover.

I began by temporarily joining two 5/8" surfaced aluminum plates using screws in a pair of their diagonal corners. The top plate will eventually become the cam box cover, and the bottom will become the fixture plate for both the cam box and its cover. The fixture plate's long sides will be machined parallel with the centerline through the dowel holes once they're drilled.

With the plates clamped in the mill vise, and the surface that will become the inside of the cover facing upward, I machined a .025" high contour into the plate that matched the interior cavity of the cam box but was radially reduced by .002". This operation turned out to be a leftover step from a previous iteration of my machining strategy that should have been deleted. Although it serves no real purpose in the current plan, with a bit less offset this boss could be used instead of dowels to locate the cover to the cam box. Dowels offer an additional advantage, though. They'll also perform as guide pins during final assembly when all the shafts inside the cam box must simultaneously engage their cover bearings as the cover is being inserted onto the cam box. (If you've ever changed a clutch and tried to reinstall the transmission while lying on your back under a car, you'll appreciate the usefulness of guide pins.) Clearance holes for the screws that will eventually secure the cover to the box were also drilled through both plates using the hole coordinates taken from the cam box.

The cam box workpiece was next mounted in the vise, and its bored center hole used to establish the reference for the dowel hole drilling operation. The cover/fixture plate combo was temporarily attached to the cam box using long 2-56 screws in most of the cover's mounting holes. Pilot holes for a pair of 3/32" dowels were then drilled through both plates and into the cam box using deep drilling parabolic bits. The long sides of the fixture plate were then machined parallel to the centerline through the dowels before finally being unbolted from the cover.

After reaming the pilot holes, dowels were pressed into the cam box. The pins were left 3/8" high which will place them flush with the top surface of the installed cover while also providing a generous guided gap during assembly so the cam box shafts can be nudged into their cover bearings. Thousandth-over holes in the cover and fixture plate provide snug fits between either of them and the cam box. When only the cover is used with the fixture plate, temporary oversize pins are lightly pressed through both provide a similarly snug fit.

The cam box workpiece was returned to the vise, and its center hole re-indicated. After temporarily installing the cover plate with a couple mounting screws, counterbores for the heads of the mounting screws were bored into the cover again using coordinates taken from the cam box. With the snug-fitting dowels, and no place to grab, it's already difficult to separate the cam box from its cover - something that will only get worse after the bearings and shafts are installed. To aid removal, I converted two of the 2-56 mounting screws, one adjacent to each pin, to 6-32 jackscrews. The cam box's previously tapped holes in those locations were filled with steel screws and milled flush to provide a durable jacking surface.

While the cover was still mounted to the cam box and set up on the mill, a decorative pattern of convex ribs was milled into its outer side. I duplicated Draw-Tech's stunning design which may be a little ambitious for someone without CNC capability. An alternative for a manual machine might be the same pattern but instead with concave ribs milled into the cover using a ball mill.

The last operation on the cover side of the fixture plate was to pocket out some clearance for the ribs just milled on the side of the cover. The cover will eventually be polished, and this clearance may prevent its surface from being marred during the later boring operations.

The fixture plate was finished up by preparing its back side for mounting up to the rear face of the cam box. For convenience, the cam box's center was transferred onto the centerline of the fixture plate's already drilled 3/32" dowel holes where a matching through-hole was bored. A second pair of dowel holes was then drilled and reamed to accept the 1/8" dowels located on the rear of the cam box. Drilled/tapped holes for the cam box's five attaching screws were also added. The fixture plate will not only help locate the positions of the cam box bores, but it will also back up and support its thin rear surface during their machining.

With the fixture plate completed and the machining of the cam box and its cover taken as far as possible with the workpieces still rectangular, it's finally time to machine their perimeters. Unfortunately, I've been noticing that my Tormach's spindle has been running unusually hot during the past several weeks. After the four hour long but very light milling operation on the cover's ribs, the tool and toolholder were so hot that I could barely hold them. The spindle turns smoothly by hand, and there's no abnormal noise under load. The runout, though, is now almost three tenths, and my notes show it was just over a tenth about a year ago. Replacement bearings were ordered last week, and so I hope to rebuild the spindle this weekend before beginning the heavy cutting on the case's large workpieces. Those bearings have logged a lot of machining time including a handful of crashes during the twelve years that I've had the machine, and so I'm really not disappointed that it's time for a rebuild. - Terry


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## mayhugh1

Replacing the bearings in my mill's spindle was relatively straight forward even though it took the better part of a day. As it turned out, the hardest part of the rebuild was the very first step which was getting the pulley off the spindle shaft. I did heat the cartridge housing to 300F in our oven before installing the new bearings, and much of the rebuild time was involved with the heating and cooling of this massive chunk of metal. The lower bearings had a slight tinge of color to them, but no signs of spalling. Setting the preload was a bit unsatisfying as it's one of those things that's hard to tell when you've got it just right. But after a couple tries, the runout is back to a tenth and the tooling is running somewhat cooler.

There's a lot of scrap associated with a part like the thick teardrop-shaped cam box sitting in the middle of a rectangular workpiece. My goal was to save some machine time by not turning it all into chips, but in the end it would have been much cheaper to have just chewed it all up.

The periphery of the cam box/cover assembly was machined in two separate operations with each having their own setup. The first was a roughing operation that milled a deep slot around the part's perimeter using a long corncob end mill while the workpiece was clamped securely in the mill vise. In aluminum and without flood coolant this can be a risky operation because with the cutter fully engaged in a deep slot, chip evacuation and built-up edge become major concerns. The operation ended .050" short of cutting completely through the workpiece so a bandsaw could be used to safely separate the part from the surrounding scrap. In addition, .030" safety stock was left completely around the perimeter of the part for the final finishing operation(s).

The reason why my starting workpieces may seem excessively large is because it was necessary to leave room for the end mill to pass safely between the part and the jaws of the vise. The workpieces were originally sized for a long 3/8" diameter cutter that I had planned to purchase just for this project. When I decided instead to use a 1/2" eBay special that I already had on hand, the larger diameter cutter didn't leave quite enough stock to counteract the clamping forces of the vise as the slot depth approached the bottom of the workpiece. As a result, the cutter was momentarily pinched in three places where the material around workpiece collapsed ever so slightly. With the conservative metal removal rate I was running, the machine had enough reserve to power through the pinch points even though its moans were those of an impending crash. If the cutter's flute length hadn't been longer than the depth of cut, the results might have been more spectacular. Fortunately, the gouges left behind in the part didn't exceed the depth of the safety stock.

I expected the finishing operations to be much less eventful, but I managed to make a bad last minute decision that became pretty expensive. For the finishing operations the workpiece for the right half crankcase was clamped in the vise for use as a machining fixture and the crankshaft center hole used to establish the machine's work offset. The cam box was packed with modeling clay wrapped in 'Cling Wrap' to add some dampening mass to maybe help with the quality of the final surface finish. A long($) 3/8" diameter four flute carbide cutter was used for the finishing operation, and the plan was to remove the .030" excess stock in two passes. In order to get a clean bottom corner, these operations were set up to continue .015" beyond the bottom of the part and into the sacrificial stock left on the outer face of the right-half crankcase specifically for this operation.

Before starting the finishing operations, I made a last minute decision to machine away the remnants of the bandsaw scrap still attached to the bottom of the part. This was done to avoid chatter marks in the surface finish that would likely occur when the 2-1/2" long cutter ran into the scrap during the first finishing pass. To cleanly remove the scrap I set up another contouring operation for the finishing tool using the same .030" offset that had been used for roughing. My mistake was that in order to avoid cutting air for most of the operation, I set the operation up to begin just above the layer of scrap.

This was a big problem because my cam box periphery contains two .200" radius'd inside corners. When the CAM software created the profile for the roughing pass it left more than the .030" offset stock in these corners since the cutter diameter was too large to reach their insides. When the profile for my impromptu pass was created, even with the same .030" offset, the 3/8" cutter was able to access the additional corner stock left behind by the roughing pass. And that's exactly what it did just seconds into the operation and with a full 1.9" depth of cut. The machine didn't have enough power to bail me out of this one, and it abruptly crashed just before breaking that very expensive cutter and ruining the collet. Again, the safety stock protected the part from the carnage I created. In the twelve years I've owned the Tormach, I can remember hitting the emergency stop button four times, and now two of those have been involved with these case parts.

After recompiling the operation to start at the top of the part, the remainder of the finishing steps went as planned. I didn't have another 3/8" tool with 2-1/2" long flutes, but I was able to get by with grinding down the lower portion of the shank of a shorter tool. Hoping that I've learned from my mistakes and that my machining process is now debugged, my next step is to do it all over again with the crankcase halves. - Terry


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## doc1955

Nice end product  I can relate to  roughing with a larger end mill then having issue in the corners with a finish cutter. But in the end she looks really nice!! I'm still in the modeling stage and doing some changes here and there.


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## mayhugh1

Doc,
Did you have any problems matching up the perimeters of the two crankcase halves and the cam box?
Terry


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## doc1955

mayhugh1 said:


> Doc,
> Did you have any problems matching up the perimeters of the two crankcase halves and the cam box?
> Terry


Not sure if I did those were modeled up some time back. I do know I have been struggling with the drawings and have changed things to suit me so if I did I'm sure I just changed it so they matched.I have all the externals modeled up starting on the internal stuff. I thinking of building this engine next but I have been modeling up the Hoglet at the same time and may do that one first. If I do the Hoglet I'm going to change it to have a full lower end case. Sitting here I do remember I had to make some changes on the case as they didn't match up. Sorry I don't remember what but I do remember putting the pieces together and then struggling to try and figure it out and then just changing it so they would match up.


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## kvom

I had missed this build thread until today and was happy to catch up on another of Terry's builds.  As always lots of good machining tips.

The "tyranny of the corner" got you like it has me in the past.  A good article by Bob Warfield on "plunge milling" showed me that roughing deep profiles by repeated plunges (similar to chain drilling) is often the best strategy for smaller mills as the Z-axis is almost always more rigid that X or Y, plus there's no side forced on the tool.

The clay packed into the chamber to reduce resonance was new to me.  Good tip for making thin walls.


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## TheHomeMechanic

Can you actually machine all this on a manual mill? It's very nicely done. I'm new here so i have not much experience yet.


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## mayhugh1

My plan to machine the peripheries of both crankcase halves together as an assembly remained unchanged even though their stack-up was going to be greater than that of the cam box and its cover. Since one face of each workpiece still contained some excess stock, my first steps were to remove as much of it as possible in order to minimize the total height. The right-half crankcase workpiece would be on the top of the stack, and its top surface was finish machined first. After facing off the sacrificial stock left behind after the cam box machining, the groove for an o-ring that will eventually seal the crankcase to the cam box was machined.

The location and orientation of each crankcase half inside its workpiece is precisely known. The dowels insure the two halves can be consistently assembled before and after being cut free from their workpieces. The dowel centerlines, which are parallel to the long sides of the workpieces, define the parts' orientations with respect to the fixed jaw of the vise. The crankshaft center hole, bored through both centerlines, provides the machining reference.

Although not necessary, it was convenient to machine the pockets for the crankshaft bearings and the rear shaft seal while the workpieces were still rectangular even though the parts' orientations really aren't important for these particular operations. Light-to-moderate press fits, determined by a few practice pockets on a piece of scrap, were used for all three. Even after twelve years my Tormach can still interpolate a circular pocket that's x-y symmetrical to better than three tenths. Since the bearings are open style, they won't be installed until after all the crankcase machining is completed.

The workpiece for the left-half crankcase will be on the bottom of the stack. Its backside surface also contained some excess stock that was faced off. The two workpieces were then bolted together using the eight crankcase fasteners that will be used to finally assemble them. In this set-up, the bottom workpiece is too short to contact the vise jaws, and although the top workpiece sat higher in the vise than I would have liked, pinching wasn't as much of a risk as it was during the machining of the cam box.

The crankcase fasteners alone wouldn't prevent the crankcase assembly from falling free from the top workpiece once the slot depth reached the seam between them. Rather than add additional fasteners outside the perimeter of the crankcase to keep the assembly intact, I decided to let it to drop. The roughing slot operation would be restarted after removing the carcass of the top workpiece and re-referencing the machine to the crankshaft hole in the bottom workpiece. This effectively cut the slot depth in half and decreased the risk associated with the remainder of the machining.

As before, a 1/2" corncob roughing end mill was used to machine the .030" offset slot around the perimeter of the assembled pair. Admittedly, in this operation, I wasn't using the tool as it was intended to be used since I was essentially cutting only with its tip. With the very shallow depth of cut taken per revolution around the contour, efficiency was very poor. Without flood coolant, though, I was more concerned about re-cutting chips inside the slot and creating a built-up edge on the cutter than I was about tool life. My hope was that the corncob flutes would be better suited for dealing with the re-cutting than those on a conventional end mill.

The periphery machining was compiled to stop short of cutting completely through the bottom workpiece since some additional features were required on the rear surface of the left-half part. Two finishing passes were made on the perimeter of the assembly before completing a bit of additional machining on the mounting arms of the right-half part. I don't normally run two finishing passes, but a lot of insurance stock remained after roughing. It was best removed in two passes with only the final one being an actual finishing pass. When completed, the periphery machining of the right-half crankcase was finished, and it was removed from the mill.

The left-half crankcase periphery machining was also completed, but a few additional operations remained for its rear face. Since performing these would cut the part free from its workpiece before they could be completed, the slot was filled with Devon Five Minute Epoxy to retain and stabilize the part inside its workpiece during these operations. When completed, the workpiece was heated in an oven for a hour at 350F in order to release the epoxy. While wearing oven mitts, the part was easily and cleanly pushed out of its still hot workpiece.

All four case components fit together perfectly with no filing or blending required to match their adjacent surfaces. After machining the bores for mounting the cylinders and oil fittings, the crankcase halves will be bead-blasted to give them a faux casting appearance. The cam box will eventually be finished similarly, but first there is a lot of work to be done on its internals. - Terry


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## mayhugh1

More Photos...


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## doc1955

They look really nice good job!
I'm working on the Hoglet now redoing the lower end to make it a fully enclosed bottom end and still have the variable timing set up.  I'm planning on building the Hoglet first then the Knucklehead if I find the time this winter.
 You have done a nice job on the case set up man I hate working with long end mills like that. When I get to that stage (if I ever do) I'm going to try load the pieces on the alignment dowels so I can do one piece at a time (we'll see). 
You need to be happy with the way yours look and I must say you take some really nice picture also every time I try to take stills they end up blurry.


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## mayhugh1

doc1955 said:


> I hate working with long end mills like that. When I get to that stage (if I ever do) I'm going to try load the pieces on the alignment dowels so I can do one piece at a time (we'll see).


That's probably what I would do if I had it to do over again. What I did was just to see if I could do it. The part I enjoy most about this hobby is planning complicated machining setups, but in this case there were too many steps and too much risky effort that I wouldn't recommend to anyone else. -Terry


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## mayhugh1

On long term projects I like to build up subassemblies that I can play with and test along the way. Breaking up a complicated build into a checklist of mini-projects provides some short term satisfaction and incentive that helps keep me going on long term projects. My goal for final assembly is, as much as practicable, to end up integrating a collection of known working blocks rather than fitting and first-time assembling individual parts.

With the cylinders and head assemblies completed, it seemed reasonable to next prepare for the crankshaft build-up since only the cylinder deck machining remained to complete the crankcase. This included the bores for the cylinder skirts as well as the drilled and tapped holes for the cylinder mounting studs and oil fittings. When this was completed, holes for the motor mounts were drilled and tapped into the bottoms of the crankcase mounting ears. The crankshaft halves were later bead blasted and the crankshaft bearings pressed into place. The rear oil seal will be pressed in just before the crankshaft is finally installed.

Some sort of assembly stand will be helpful during the crankshaft build-up, and so I fabricated something simple that I'll use now for assembly but later add to for display. Its uprights were machined from 3/8" x 1" hot rolled steel that were welded onto a 6"x12"x3/8" steel plate. It's a heavy stand that shouldn't move around while the engine is running, but I wanted to allow the engine to freely shake while idling. I machined a pair of motor mounts from a sheet of 1/2" thick rubber that I bonded to the stand's uprights. I don't like machining rubber, and it's really something of a 'stretch' to even call it machining, but after a full frustrating day I had a pair of mounts that I could live with.

The SHCS's for the motor mounts screw in through the bottom of the engine to avoid later conflicts with the starter motor. Holes were drilled through the baseplate directly below them so they could be accessed with a hex wrench. The lengths of the mounting bolts were carefully trimmed so they bottom out in the tapped holes in the crankcase before significantly compressing the rubber. In order to keep the bolts in place, their heads will later be cross-drilled for safety wire.

A hole was also drilled through the baseplate directly below where I plan to add the cam box's oil drain plug. With the engine sitting so low on its stand, there'll be no room between it and the baseplate for a drain pan. Instead, used oil will be drained through the baseplate and into a container held below it.

The stand was finally rattle-can'd with the Rust-Oleum textured paint that I've used on a number of engine stands since it easily hides imperfections in unfinished and welded surfaces. After a couple days of curing, it also seems to be resistant to engine fluids. I usually machine an integral drip tray into the baseplate directly below the engine, but that needed to be done before the stand's uprights were welded in, and I forgot to do it. Hopefully, with all the o-rings I've added to the engine, leaks won't be a problem.

The next step is to begin work on the crankshaft. This should be a real learning experience since the crankshaft construction in the downloaded drawing closely parallels that of the full-size engine with its three piece construction and tapered-ends crankpin. I've been studying Youtube videos dealing with rebuilding Harley crank assemblies, and what's ahead looks pretty hairy. - Terry


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## kuhncw

Very nice work, Terry.  Thanks for posting the photo showing how you protected the parts for bead blasting.

Chuck


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## natalefr

Awesome !


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## stragenmitsuko

Is it me or is it just the camera angle ? 
Somehow the cilinders seem to be pretty small compared to the crankcase . 

I like the bead blaseted look . 
What kind of blasting abrasive do you use ?


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## mayhugh1

stragenmitsuko said:


> Is it me or is it just the camera angle ?
> Somehow the cilinders seem to be pretty small compared to the crankcase .
> I like the bead blaseted look .
> What kind of blasting abrasive do you use ?



Well, now that you mention it ...
Here's a photo with the heads sitting on the cylinders - much better.
By the way, I just use glass bead media from the local harbor Freight.


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## stragenmitsuko

Still ... looking at some pictures on the netthe cilinders seem to be taller then the cranckase .


Please don't consider this as criticism , its just an observation


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## mayhugh1

I've owned several motorcycles (all Asian), but in thirty years of riding I've never been inside a crankcase. After studying Draw-Tech's crankshaft drawing, I spent several hours watching Youtube videos to get some background and familiarize myself with Harley crankshafts. I developed a particular fondness for a series of videos (Youtube search 'Tatro Machine Knucklehead') dealing with an actual Knucklehead engine rebuild. Although it ended tragically for the owner, it was apparent that Draw-Tech's crankshaft was very similar to the one in the original full-size engine.

The full-size crank assembly has two shafted flywheels and a crankpin with ends that are tapered and threaded. During assembly, large nuts, tightened to some 100 ft-lbs, draw the pin into matching tapers machined into the inside faces of the flywheels. The assembly is then mounted in an on-centers alignment fixture so the runout's of the two outer shafts can be simultaneously monitored. What seems like a brutal alignment process is actually some intelligent hammering, spreading, and pinching of the two flywheels in just the right places to reduce the typical .010" starting runout to a couple thousandths or less. The connecting rods use roller bearings on their big ends, and so they have be installed on the pin before assembly.

Many of us have machined perfectly adequate crankshafts with simple cylindrical crankpins attached to the crank throws with pinch bolts. Several alignment issues disappear if the crank halves are machined from a single billet, and the crankpin hole is drilled and reamed before sawing the halves apart. Since this technique is time consuming and creates a lot of waste, some builders instead opt for a five piece assembly with separate shafts.

The tapered crankpin is capable of handling the power requirements and allows the rods to be serviced. But it adds significant complication and risk because tapers must be machined in four individual parts, and any imprecision in their machining can create misalignment in the final assembly. In addition, the major diameters of the flywheels' tapers, being non-measurable two dimensional quantities, will determine the depths of the crankpin inside the flywheels and therefore the side clearances of the rods in the final assembly.

These concerns create reasonable arguments for tossing aside what will be a hidden-from-sight scaled-down version of the crank and instead fabricating a more conventional model engine crankshaft. Besides 'wimping out', though, this would require reshaping the crank halves to accommodate the pinch bolts which, in all likelihood, would significantly reduce the rotational inertia of the relatively massive Draw-Tech crank. An alternative would be a conventional crankpin held in place with taper pins, but I was concerned about being able to remove them if the rods ever had to come out.

All engines, big or small, benefit from some amount of rotational inertia to keep them rotating between plug firings at low rpm's. One and two cylinder four-cycle engines benefit the most. (It turns out that Harley flywheels are so effective that some owners reduce their older engine's idle speeds to the point where the oil pump can barely function, just to show off that world famous staccato.)

The Draw-Tech Knucklehead includes an additional external brass flywheel, reminiscent of a steam engine, that adds additional inertia to the engine's rotating mass. I plan to replace this with a faux roller sprocket or a belt drive that will look more at home on a motorcycle engine, but it won't be as an effective flywheel. I don't want to give up the rotational inertia of the Draw-Tech crank assembly, and so I decided to stick closely with its design. I had enough Stressproof on hand for two attempts. The drawing called for a finished crank flywheel diameter of 2.83", but since my material was only 2-3/4", my crankshaft flywheels ended up a bit smaller.

My plan did not include turning the crankshaft between centers as one might expect. The modified cross slide on my Wabeco lathe won't allow a cutting tool to access the tailstock end of a workpiece supported by a conventional dead center. The stock cross slide will allow this, but its lightweight construction greatly limits the lathe's precision and surface finish quality. When using the tailstock, I often have to use an expensive long nose live center that can add up to three tenths of its own runout. At the end of the day, turning between centers can be somewhat counter-productive on this lathe.

Construction began with skimming the workpiece o.d. to a consistent diameter in my Enco lathe where I faced both ends and center-drilled one. The workpiece was then moved to a three-jaw chuck in my little Wabeco where, in conjunction with the tailstock, the o.d. was taken to its finished diameter over as much of its length as I could access including the portion that would eventually become the flywheels. The outer shaft was then turned and fitted to the outboard crankcase bearing. At this point, the o.d.'s of the shaft and the flywheels were concentric, and what will become the outside face of the outer flywheel was normal to their axis. A dial indicator showed all three TIR's were less than two tenths with the tailstock engaged and three tenths with it disengaged.

The chuck, with the workpiece still attached, was then taken to the mill where the crankpin through-hole was drilled and reamed. The flat-back chuck insured the hole ended up parallel to the axis of the bearings and identically drilled through both flywheels. A recess for the crankpin nut was then machined into the face of the outside flywheel, and material required for balancing the assembly was removed. Some practice material in a vise is visible in the photo of this operation. A 3/8" end mill with more than two inches of stick-out was required to work around the shaft, and some fine tuning was required to determine the speed, feed, and doc for minimum chatter.

The workpiece was returned to the Wabeco in a six-jaw set-true chuck so the shaft on the cam box side of the crank could be turned. The workpiece was gripped on the finished flywheel diameter which I was now only able to indicate to what would have to be called +/- three tenths because the TIR reading had picked up a second bump in an opposite direction to the first one. The Wabeco and tailstock center bearings left their runout imprinted on the workpiece when it was turned the first time, and now with the workpiece back in the lathe but oriented differently on the spindle, a second copy of their runout was now being indicated. I tried alternate orientations, but differences between the chucks I was using prevented me from improving it.

The fresh end of the workpiece was then center-drilled for the tailstock center, and the shaft diameters for the crankshaft and cam box bearings were turned and fitted. The measured TIR of the shaft had returned once more to two tenths with the tailstock engaged and three tenths with it disengaged. Although it appeared that the second bump was gone, it really wasn't. A second copy of the Wabeco and tailstock runout was now machined into the workpiece, and both will appear when the runout's on the ends of the two shafts are compared.

The chucked workpiece was returned one last time to the mill where the second nut recess and the balance area were machined on the face of the cam box side flywheel.

I slid a couple ball bearings from my scrap collection onto the two shafts so a TIR baseline measurement could be made with the work in progress sitting on a pair of v-blocks. The result was .001" which included the blended humps in the workpiece TIR as well as the runout's of the two ball bearings. Just for interest, I also measured the three runout's with the workpiece held between centers on my lathe. Since the workpiece hadn't been turned between centers, I wasn't expecting stellar results. However, the TIR of the output shaft measured .002", the cam box shaft measured .001", and the flywheels measured .0025". If this had been an actual Knucklehead crankshaft completed at a Harley assembly plant, it would have actually (although just) passed their QC.

I suspect the first measurement is probably the one that's most important to me. After completing the machining and assembly, my current plan is to compare the runout's of the two flywheels while the shafts are in ball bearings on v-blocks to see how well the machining turned out. - Terry


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## Draw-Tech

I have been following your build, It looks like you will be the serial number 002
I wish I had a cnc machine, you make things so easy. GREAT JOB, The crank was designed from pictures, scaling in cad, if you need any files, send me a PM
I would like to hear from you, again "AWESOME"
Jack
Draw-Tech


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## mayhugh1

The crankshaft halves were sawed apart in the bandsaw, and each flywheel finished up in the lathe while being supported by its shaft in a collet chuck. Before each facing operation, the outer edge of the already finished face was indicated and the part rotated in the collet for minimum indicated wobble (for some reason it made a difference). Both halves wound up at about two tenths.

While thinking about how I was going to offset mount the flywheels in the lathe for their taper operations (my Wabeco four jaw can't handle the long shaft sticking out the backs of the flywheels), I made a fixture that I hoped would allow me to accurately assemble the flywheels without having to hammer on them later. Basically, what I came up with was a sleeve to hold the two flywheels in alignment while the crankpin nuts were tightened.

Although Delrin would have been a better choice, I machined the sleeve from a block of mystery plastic that I had on hand. It was faced to a thickness of 1.6" and its o.d. turned to roughly 4 inches. After boring out its center to about 2-1/4 inches, the sleeve was transferred to the bandsaw where three equally spaced 3/8" long radial cuts were sawed into its outer perimeter. On the mill, one of these relief cuts was opened up into a 3/4" wide slot, and a shim was machined to fit tightly inside it. Finally, a saw cut was made through the center of the slot to open it up to the bore.

With the shim in place inside the slot, the workpiece was returned to the lathe chuck with the jaws centered between the relief cuts. The purpose of the cuts is allow the jaws to uniformly close the sleeve around the shim (and later around the crankshaft flywheels) as they're tightened. For safety, I ty-wrap'd the shim in place while the i.d. of the sleeve was finish-bored to the exact o.d. of the crankshaft flywheels.

With the shim discarded, the crank halves will be assembled inside the sleeve with the connecting rods sticking up through the slot. This assembly will be done with the sleeve clamped in the three-jaw chuck while the crankpin nuts are tightened.

In order to offset turn the flywheel tapers, I machined a carefully squared-up aluminum spacer block to stand the parts off the surface of my five inch four-jaw chuck. This spacer provided the needed clearance for the shaft, and it moved the workpiece away from the jaws so it could be easily accessed by the tiny boring bar used to turn the tapers. A concern, though, was that this block would be yet another piece in the accuracy chain. The hole for the flywheel shafts was drilled and reamed with the spacer mounted in the chuck and tight against its face. The pinch bolt machining was done later on the mill.

Since I planned to spin the nearly 20 ounce unbalanced load in the little chuck at close to 1 krpm I was concerned about vibration. I carefully computed the requirements for a pair of counterweights that I bolted to the chuck. With these weights, the loaded chuck showed no signs of vibration even at 1500 rpm.

In addition to indicating the pilot holes for the tapers, it was also important to indicate across the faces of the flywheels in two orthogonal directions in order to ensure the axis of the taper ended up parallel to the axis of the shaft. Any perpendicularity errors will be magnified during assembly and affect the shaft TIR's. The spacer block that I had to use complicated the setup because it tended to lift during the jaw adjustments. Protective steel shims were used between the jaws and the spacer block in order to prevent the jaws from biting into the aluminum and making it difficult to keep the block down against the chuck. After a lot of tweaking, I was able to obtain nearly identical TIR's on both flywheels: .0005" on the pilot hole, zero along one surface direction, and .0015" along the other direction. I didn't like the .0015", but it was the best I could do. After all the prep work, the two minutes of lathe work were uneventful.

In preparation for the crankpin, I machined the nuts that will be used on its ends. Although shortened commercial nuts could probably have been used, I machined a pair from drill rod that I hardened. I wanted the finished nuts available before lathe-threading the crankpin so I could turn its threads for a close fit to them. - Terry


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## mayhugh1

I ran into major problems while trying to machine the crankpin. The crankpin sets the separation between the flywheels which in turn establishes the clearance for the connecting rods and the thrust clearance of the crankshaft. The smallest of these (and it's actually pretty generous) is the specified .004" thrust clearance. In this engine with its tapered crankpin, it would have been much easier to complete the crankshaft before machining the crankcase. With the crankcase already finished, however, the clearances now depend upon the exact placement of the tapers on either end of the crankpin.

My original plan was to CNC machine the entire crankpin in one operation on my Wabeco, and let the CAD/CAM software handle the placement of the tapers. I fully expected to have to machine a few trial parts in order to fine tune the operation, but after an entire day of head-scratching and scrapped parts, it became obvious that something was way off.

Eventually, I recalled problems with a much earlier project in which I discovered that my CAM software doesn't seem to properly handle the profile of a lathe tool's cutting tip when turning non-cylindrical parts. I tried to characterize the error so I could compensate for it by changing the design of the pin. However, tool and/or part deflection as well as the lathe's own taper issues were combining with the runout of the live tailstock that I was using to overwhelm the part's accuracy requirements. Errors from all these sources, and probably others, were inconsistently combining to give an essentially random result on every part that I made. In addition, since I was checking the results by assembling a finished pin with the flywheels (sans nuts) and measuring the total outside width, I missed the fact that the errors were different on each end of the part.

At this point it would have been reasonable to modify the crankcase or the flywheels to accommodate one of the already finished pins. However, measurements showed there were almost half degree differences between the taper angles on the two ends of the parts. Although the pins appeared to fit the flywheel tapers quite well, I was concerned that the angle errors might show up later as alignment inconsistencies.

My next attempt was to machine only one end of the pin at a time. The tailstock was no longer needed, and the reduced stick-out would mean less deflection. Since I was using polished drill rod with an o.d. that matched the i.d. of the connecting rod bearings, I compiled a single program to turn the exact same taper on each end of the part. This required indicating each end of each part, since my so-called 'set-true' chuck had to be re-tweaked after every spin-up. In order to reduce the effects of the CAM error, I changed the insert to a DCMT21.50 which is a sharp diamond-shaped finishing insert with a nose radius of only .008" - half of what I had been using. I also compiled the cutting program to take only .003" (radius) d.o.c.'s.

Two new issues arose, however. The workpiece had to be pre-turned to an exact length, and the nose of the cutting tool had to be perfectly centered over the Z=0 edge of the part. Since typical errors (for me) in either one of these steps could easily exceed the part's per-side error budget, I decided that I'd just have to make parts until I got at least one that I was happy with.

Even though, with the help of a 10X magnifier, I became pretty good at centering the tool over the starting edge of the part, another error crept in over time that kept me off balance. The delicate tool tip wore quicker than I was accustomed to, and its tip slowly and asymmetrically changed shape. This created a continually changing error over the entire run of parts that kept me chasing my tail.
Eventually, after more than a dozen parts, I had five with thrust clearances I could live with. I threaded all five so I could see how well the TIR's had been controlled during all the operations require to get to a final assembly. I've included a photo of a page in my notes that shows all the results. I was also anxious to see how well the alignment sleeve worked and how consistently I could reassemble the same set of parts.

The sleeve worked as well as I had hoped. As the notes show, the final shaft TIR's were generally less than .001". As expected, there was a lot of minute structure in the runout's due to all the tiny errors accumulated from so many sources. In only one or two parts did the errors combine constructively and cause the TIR to exceed .001".

The alignment sleeve worked very consistently and gave the same TIR results on repeated assemblies using a couple different pins. I also compared the sleeve alignment with an alignment done by tightening the nuts with the flywheels clamped in a v-block since this was essentially the assembly method used in one of the Youtube videos that I watched earlier. My best result using that method was on the order of .008" which was in line with the results obtained in the video.

The next part will be something less critical and hopefully more fun. I'm currently planning to machine a double roller sprocket for the engine's output shaft that should add a little more rotational inertia to the crankshaft. - Terry


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## vederstein

I, as many others, are amazed by the work you do.


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## kvom

Once you were turning each end separately, you could have turned the tool so that the edge was parallel to the end face.  Then setting Z would mean touching the tool and subtracting the radius of the tip to get z0.

Is your CAM error failure to properly consider the offset needed before commencing the taper?  

In any case, it all worked out well in the end.


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## mayhugh1

Kvom,
What you suggest sounds reasonable so long as an eye is kept on the cutting direction and d.o.c., but even then there are a few issues. I made a couple sketches. The first one shows the tip oriented as the software expects. When the insert type is entered into the software, it knows about its shape and it expects its tip is located at z=0 as shown by the red centroid marker in the drawing. The software supposedly uses this tip and the shape of the insert to compute the tool path trajectories. Hopefully, for d.o.c.'s greater than the radius of the tip, it continues to properly account for the shape of the insert by including its straight cutting edges. On my particular parts, the software generated roughing passes that cut while moving toward the headstock, and finishing passes that cut while moving toward the tailstock. I had control over the directions, but I elected to allow the software to selected them.

The second sketch shows the left straight edge of the insert rotated so it's parallel to the face of the workpiece and that edge shifted toward the headstock by an amount equal to the radius of the insert's nose. When z=0 is set, the software will assume the center of the cutting tip is located as shown by the blue centroid marker which is now located asymmetrically on the insert. When cutting toward the headstock with d.o.c.'s greater than the radius of the tip (in this case greater than .008") the software will assume it is using the left-side straight cutting edge when it really isn't. When cutting toward the tailstock with a d.o.c. greater than (in this case) about .002" it will actually be cutting on the right-side straight edge when it really isn't.

In my experience, it's hard to set a lathe tool right at z=0 (within a thousandth or two) without facing the end of the part and immediately zeroing the Z DRO. Rotating the tool so its edge is exactly parallel with the face of the part introduces another piece of the setup that needs to be accurately done or the amount the tip is to be offset will be in error. - Terry


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## kvom

My CAM allows the tool shape to be rotated, and as well only does the finish pass towards the headstock in cases like this, so I can see where in your case it wouldn't work.  As for Z0 being within .001, my little CNC lathe would be hard pressed to get anywhere near that.


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## JamesDTaylorSTL

Wow! Truly incredible work! And all the time taken to help others do a build! I never liked my EVO's heavy,boxy rocker arms so now I know how to make better ones!
Thanks!


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## mayhugh1

With the crankshaft temporarily installed in the engine, and before starting work on the motor sprocket, I wanted to make a quick trial assembly of all the major parts machined so far. In order to install the cam box cover, the recess for the crankshaft's end bearing had to be bored. With the cover mounted in its machining fixture, I used my previously recorded coordinates for the crankshaft location to bore a flanged recess for the ball bearing. This particular hole is pretty important because it not only supports the far end of the crankshaft, but it will also be a reference for locating the rest of the cover bearings that will be machined later.

Unfortunately, when I tried to slide the doweled cover onto the cam box which was doweled to the crankcase whose halves were doweled together, the cover wouldn't begin to go on. After a few hours of measurements, I was pretty sure that everything in the engine that could cause such an error was correct, and that I must have bored the recess for the bearing in the wrong location.

In order to check the bearing's location, I machined a bronze blank to snugly fit the recess, and I added witness marks to both it and the cover to keep track of the blank's orientation. The crankshaft was then replaced with a length of drill rod whose end had been turned to a point so I could transfer its location to the blank. With the blank then set up in a collet chuck under my mill's spindle microscope, I discovered the recess was perfectly located in the y-direction but was off by exactly .010" in the x-direction. Evidently, I previously recorded an incorrect DRO reading - something that seems to be happening more frequently these days.

I used the transferred mark to drill and ream a hole for the shaft and then returned what was now a bronze bearing to the cover. The fit with the actual crankshaft now seemed perfect, and so I Loctite'd the bearing in place. I left its nose a little long so it would be the first bearing to engage the crankshaft during the cover installation. Since the shaft will be just above the oil level inside the sump, the bearing will receive plenty of lubrication, but I'll also mill an oil groove on the end of the crankshaft for extra measure.

While inside the engine, it occurred to me that the crankshaft assembly along with the crankcase oil will probably occupy 90% of the volume inside the crankcase. In addition to normal blow-by, the pistons' asymmetrical pumping action will create significant pressure pulses inside the crankcase. The crankcase is sealed except for the oil return lines coming in from the engine's top-end and a pair of oil-submerged holes connecting the sumps of the crankcase and the cam box. Since the crankcase pressure would have to overcome the oil column in order to vent into the cam box, it might instead pressurize the oil returns and cause the top-end to flood with oil.

In order to reduce the chances of this happening, I drilled a 3/16" vent hole above the oil level connecting the crankcase with the cam box in order to increase the effective volume of the crankcase and reduce the pressure pulses. The cam box will later be vented to the atmosphere, probably with a vented oil filler cap.

Inadequate crankcase ventilation can even prevent a engine from running. I once demonstrated this on my Hodgson 9-cylinder radial. Blocking that engine's crankcase ventilation will cause it to stall. - Terry


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## mayhugh1

The Draw-Tech Knucklehead includes an external flywheel to supplement the rotational inertia of its crankshaft. Rotational inertia provides the angular momentum needed to keep the crankshaft in a one or two cylinder 4-cycle engine spinning between its relatively infrequent plug firings. Because rotational inertia scales exponentially with a rotating mass's diameter, the flywheels inside a scaled-down motorcycle engine crankcase are seldom sufficient to provide a satisfyingly low idle speed. The equation for the rotational inertia of a ring, which is the most important part of a flywheel, is:

J = (m/2) * (R1^2 + R2^2)

where m is the mass of the ring, R1 is its outside radius, and R2 is its inside radius. There's an additional radius dependency hidden inside the expression for the ring's mass that, when brought out, shows the rotational inertia is an extremely sensitive function of the ring's diameter:

J = (pi/2) * t * D * (R1^4 - R2^4)

where t is the thickness of the ring, and D is the density of the metal (approximately 4.5 oz/cubic inch for brass or steel), and the sign change isn't a typo. This form of the equation is seldom found in physics texts, but it's most useful for design work. The rotational inertia of a simple disk can be found by setting R2=0.

Rotational inertia is easy to compute, but the amount needed by a particular model engine for a well-behaved idle isn't so simple to estimate. In order to test the need for the Knucklehead's huge five inch flywheel, I looked at a couple popular model engines that are similar in design and scale to the Knucklehead and known to behave at low idle speeds.

The first was Jerry Howell's 90 degree V-twin which was actually my first IC engine built some eight years ago. I calculated the total rotational inertia of its entire rotating mass to be approximately 97 oz-inch^2 with 90% of it coming from its (4"x 1-1/8" thick) external flywheel. The second engine was the 45 degree Hoglet whose plans appeared in Model Engine Builder magazine. Remarkably, at 105 oz-inch^2, its rotational inertia is nearly identical to that of Jerry's engine. Almost all of it comes from the two 4" x 9/16" thick flywheel rings integrated into the crankshaft inside its skeleton crankcase.

The rotational inertia of the pair of internal crankshaft flywheels inside the Draw-Tech Knucklehead is a healthy 26 oz-inch^2, and its external (5" x 3/4") flywheel adds another 127 oz-inch^2. Its large external brass flywheel is a clever multipurpose design that includes a rope start pulley as well as some limited cooling from its fin-shaped spokes. For my taste, though, it's too large and doesn't look at home on a motorcycle engine. I set a goal of 75 oz-in^2 for a new design since this would bring the total up to match the two more common v-twins. Excessive rotational inertia adds stress to the starting system and increases the torque requirement of the starter motor.

I began by juggling the paper design dimensions of a plain steel disk that would achieve 75 oz-in^2. It quickly became apparent that even with a 1-1/4" thickness, I was going to be stuck with a diameter on the order of 3.5". For a motor pulley this was way out of whack with the rest of the engine's scale.

I looked at shelling a portion of the disk and filling it with ultra-fine tungsten powder that I had on hand. Tungsten has a theoretical density of 10.3 oz/cubic inch compared with 4.5 oz/cubic inch for steel and would seem like a great candidate for reducing the flywheel diameter by some 23%. Unfortunately, this theoretical density can only be approached by casting tungsten which is impractical due to its extremely high melting temperature. I experimented with pressure sintering it, but the best density I could achieve using my hydraulic press was approximately 6.3 oz/cubic inch. This was an improvement over steel, but essentially identical to what would be expected with cast lead. Since the resulting reduction in flywheel diameter would be only about 8% (the fourth root of the density ratio), the effort involved in working with the messy and extremely abrasive stuff was hardly worthwhile.

After finally accepting the fact that I wasn't going to end up with a flywheel on the output shaft disguised as a reasonably scaled motor pulley, I thought I'd at least try to dress it up a bit. I did two partial CAD designs - one for a triple roller chain 'ripper' sprocket and another for a cogged belt drive pulley. Variations of these can be found under the primary covers of Harley motorcycles.

The sprocket was functionally designed for three 1/4" roller chains so I would have the option of using it to drive something or perhaps even to start the engine. The teeth added much more to the diameter of the sprocket than they did to its rotational inertia, and so its interior would have to be shelled and filled with lead in order to keep its diameter below that of the crankcase. The belt drive pulley was also designed to be functional and is identical, except for the number of teeth, to one that I added to my Howell V-twin so it could drive a faux transmission.

After a lot frustration, I decided to stay with a simple polished stainless steel flywheel that wasn't pretending to be something else. Although the more interesting versions would have been fun to machine, they attract attention to themselves and fact that they're wildly out of scale. A plain wobble-free polished flywheel, while spinning very close to the crankcase, might tend to fool one's eye into thinking it was actually part of a primary.

The design I finally chose to machine is shown in the last photo. At 3.4" diameter and 1.25" thick, the chunk of solid stainless steel has a total rotational inertial is 72 oz-in^2. A tapered lock bushing will secure it to the output shaft, and an integrated 1" hex will provide for drill starting engine just in case I'm unable come up with a functional electric starter. - Terry


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## GlennS

Question: if you were to add the primary chain and driven (transmission input) pulley, would their inertial weight become part of the flywheel equation?


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## mayhugh1

GlennS said:


> Question: if you were to add the primary chain and driven (transmission input) pulley, would their inertial weight become part of the flywheel equation?


Glenn,
Yes, any inertia in the load would be included. The chain would also add some frictional losses that the engine would have to overcome.
Terry


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## kvom

I did wonder where you get tungsten powder.

Tungsten rod cut into short pieces and embedded cross-wise in the flywheel rim might work.


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## mayhugh1

kvom said:


> I did wonder where you get tungsten powder.



Believe it or not, there's a consumer market for it, and you can buy it from Amazon. There's another subculture out there making their own 'high performance' fishing tackle and weights that uses tungsten powder mixed with epoxy rather than cast lead. They settle for even lower densities than I was able to achieve.  Serious Pinewood Derby dads also use it. Mine is over forty years old and was left over from a project that I was involved with in the nuclear instrumentation world. - Terry


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## RonC9876

mayhugh1 said:


> Believe it or not, there's a consumer market for it, and you can buy it from Amazon. There's another subculture out there making their own 'high performance' fishing tackle and weights that uses tungsten powder mixed with epoxy rather than cast lead. They settle for even lower densities than I was able to achieve.  Serious Pinewood Derby dads also use it. Mine is over forty years old and was left over from a project that I was involved with in the nuclear instrumentation world. - Terry


.                                                           what,


mayhugh1 said:


> Believe it or not, there's a consumer market for it, and you can buy it from Amazon. There's another subculture out there making their own 'high performance' fishing tackle and weights that uses tungsten powder mixed with epoxy rather than cast lead. They settle for even lower densities than I was able to achieve.  Serious Pinewood Derby dads also use it. Mine is over forty years old and was left over from a project that I was involved with in the nuclear instrumentation world. - Terry





mayhugh1 said:


> Believe it or not, there's a consumer market for it, and you can buy it from Amazon. There's another subculture out there making their own 'high performance' fishing tackle and weights that uses tungsten powder mixed with epoxy rather than cast lead. They settle for even lower densities than I was able to achieve.  Serious Pinewood Derby dads also use it. Mine is over forty years old and was left over from a project that I was involved with in the nuclear instrumentation world. - Terry



 What's the matter Terry, No Uranium! Tungsten is too mundane!


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## kvom

I did see another site where golfers put the powder in their club shafts, presumably for more weight at the head.


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## mitchilito

kvom said:


> I did see another site where golfers put the powder in their club shafts, presumably for more weight at the head.


I wouldn’t settle for anything less than depleted uranium ;-)


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## mayhugh1

Anyone who's looked at the Knucklehead drawings may have noticed a suggestion for fabricating its stock 5" brass flywheel that doesn't require an expensive piece of round stock. The drawing shows a built-up soldered assembly that includes a 3/4" thick ring rolled from bar stock. I considered doing something similar for my 3+ inch flywheel because the only stainless drop I had on hand with sufficient diameter to turn it was a 4" piece of 304.

I've turned a bit of 304 in the past, but I've never liked it. The issue for me is that neither of my lathes have enough power to take the depth of cut needed to get comfortably underneath a large diameter work-hardened surface left by a previous pass. Since this chunk of metal had never been used in my shop for anything other than a weight, I thought I'd finally try to make it into something useful. A flywheel is probably a good choice. There aren't any critical dimensions to try to hit with shallow passes, and its hardness could work to my advantage by producing a tough polished-looking surface right off the lathe. In any event, it would be a new experience.

I chucked the entire drop in my Enco lathe in order to first work on what would become the hidden face against the crankcase. This allowed me to experiment with inserts and their cutting parameters for turning, facing and boring. As expected, I couldn't use any of my favorite finishing tools, but at 200 rpm and .010" d.o.c. , I was able get reasonable surface finishes using some moderately raked inserts that I had.

My Enco can't handle the tooling that really should be used with this large diameter material. After changing its spindle drive belt to a quality link belt several years ago, I lost what feels like half the power at the spindle due to belt slippage. I suspect there isn't enough contact area between the import's pulley and the new belt. Since I don't do production work and modifying the pulley would require a spindle teardown, I've just been living with it.

Turning the o.d. down from 4" to 3.4" required a couple difficult hours because every pass had to be manually fed at a rate just below the point of belt slippage in order to keep the tool moving along without hopelessly work hardening the surface of the workpiece. Since the passes weren't deep enough to reach the insert's chip breaker, the chips came off as long strands of hot razor wire that invariably wrapped themselves around the chuck.

The center through-hole was drilled with a 3/8" cobalt drill and wasn't at all difficult. Its exact diameter wasn't critical because the flywheel will eventually be secured to the engine's output shaft with a tapered lock bushing. The flywheel's internal taper was the only operation planned for the Wabeco. With no back gear, its motor doesn't generate the low speed torque needed to turn tough large diameter material.

After getting a satisfactory result and much needed experience on its rear face, the disk was sawed off on the bandsaw. I had to replace the saw's bimetal blade midway through the operation, but it had seen more than its share of hours anyway.

The disk was returned to the Enco and indicated until its rear face was normal to the lathe's spindle axis. The front surface was then faced parallel to it. The third pass produced a surprisingly beautiful finish, and so I decided to not press my luck and left the flywheel .030" thicker than I had planned.

The next operation was to mill the center hub which included a one inch hex and six drilled/tapped 3-48 holes. I had designed the hub so I could use a 5/32" end mill to machine around the hex, but at the time I wasn't expecting to be working with 304. More time was spent experimenting with milling parameters so I could get through the operation without destroying a lot of cutters. It took five hours, a record in my shop, to complete the machining of that little hub including two proactive tool changes to improve my chances of getting through it.

With respect to tooling costs, I was already at the point where it would have been cheaper to have ordered a piece of 303, but I still had six holes to drill and tap. Before I was done, I had broken two drills and dulled all three of my 3-48 taps. The tapping was done manually under the mill's spindle with lots of cutting oil and took nearly an hour turning the tap an eighth turn at a time. I was probably unnecessarily work hardening the metal by not being more aggressive, but I just couldn't bring myself to work any faster. The hub's surface finish wasn't stellar, and so after masking off the flywheel's finished surfaces, I bead-blasted the heck out of it before moving onto the internal taper.

The taper operation was the sweetest of all because its smaller diameter allowed me to really crank up the spindle speed. The d.o.c.'s were programmed so there were no shallow passes. Only the taper angle was important but, unlike the crankshaft tapers, the starting diameter wasn't critical.

The taper bushing was a breeze to machine from Stressproof. Only the through-hole diameter and taper angle had to be precise. Once inserted into the flywheel, the bushing's flange needs to stand off a bit from the flywheel's hub so the draw screws can pull the bushing into the hub. Six of the flange's nine holes are clearance holes for anti-seize coated steel draw screws, and three of them were tapped for jack screws. The through-hole was reamed a thousandth undersize in the same setup used to machine the taper and then lapped to fit the crankshaft. The hole closed up minimally when the bushing was slit.

The flywheel and bushing were assembled on a piece of drill rod that had been indicated in the set-true chuck on my Wabeco. The run-outs of the faces were about a thousandth, but there was a .002" runout in the o.d. With the outer end of the drill rod secured in a rotating tailstock chuck, I took a Hail Mary truing pass across the flywheel's o.d. using a brand new .008" radius insert. I trashed the insert but got a smooth surface that I was able to polish to match the flywheel's face.

The final machining operation was the engraving of a pair of short timing marks, separated by 20 degrees, on the rear edge of the flywheel's o.d. A suitable reference mark will be engraved later on the rear of the crankcase. Since the flywheel can be easily secured at any angle on the crankshaft, one of these marks will be used to indicate TDC and the other used as a timing advance reference.

After trial fitting the flywheel to the crankshaft/crankcase assembly, the TIR measured at its o.d. was about a thousandth which was a little better than expected due the crankshaft's half thousandth runout. This creates a barely perceptible wobble on the inside edge of the flywheel that's visible due to its close proximity to the crankcase. Although it quantitatively means nothing, the flywheel gave crankshaft a 'twist-of-the-wrist' spin-down time of almost 15 seconds. - Terry


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## Naiveambition

Impressed as always to your approach.  I think I have a simplistic attitude and am anxious just to cut chips. The often indirect routes you take are just a marvel considering they are model engines.  
With this motor I've looked real closely at the full size versions, and and wandered if you could put a belt drive primary , then put the 'rolling mass' inside a faux trans,    Could this possibly keep it going as a flywheel.  using something similar to Steve hucks v8 supercharger belt .  But just a thought , I could be dead wrong


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## mayhugh1

Naiveambition said:


> With this motor I've looked real closely at the full size versions, and and wandered if you could put a belt drive primary , then put the 'rolling mass' inside a faux trans, Could this possibly keep it going as a flywheel.


I think you could.

I did this:



with my Howell v-twin, but as you can see I kept the external flywheel since that engine really wasn't a scaled anything in particular. I used the trans housing to hide the TIM-6's  huge coils and fuel tank, but the flywheel could have been moved inside as well. If I get the Knucklehead finished and running and still feel like doing more on it, I might add a primary cover and trans to it as well. - Terry


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## mayhugh1

The full-size Knucklehead uses three caged roller bearings on the big ends of its rods (the rollers ride on the hardened crankpin) and ordinary bronze bearings on the small ends. The widths of the outer cages are narrower than the center one, and so the rods' big ends wind up with equal bearing contact areas.

The Draw-Tech version uses four identical ball bearings on its crankpin and a single caged roller bearing on the small end of each rod. (The rollers will ride on hardened wrist pins.) The widths of the ball bearings are such that the big end of each rod is supported by its own pair of bearings, but because they're not rollers their effective contact areas will be much less than what is provided by the rollers on the small ends.

The SCE-45 roller bearings that I received from McMaster-Carr measured .4395" in diameter - a full two thousandths over its recommended bore. The thin metal shell on this type of bearing can sometimes be out of round and difficult to measure until it's pressed into place, but my measurements showed these were perfectly round. In addition, gage pins showed their shaft diameter wanted to be .252" instead of .250". I couldn't see how the bearing's rolled-over steel edges were going to allow them to be compressed a full two thousandths during the pressing operation, and so I performed a test.

I drilled and reamed a .4375" test hole in a piece of 3/4" thick scrap aluminum. An equivalent of the recommended installation tool was used to install one of the bearings and it was pressed in using the recommended outer edge of its lettered rim. The bearing went in, but it required a breaker bar on my one ton arbor press. A .250" gage pin was still a loose fit in the installed bearing, but a .251" pin fit reasonably well which meant the shell had indeed been compressed some.

I was afraid that a .002" interference fit might be damaging to the small ends of the aluminum pushrods after they had accumulated a number of hours of machining time. A cock-eyed installation due to galling would be a problem. A roller bearing is probably less tolerant of rod and piston machining errors since issues with twist that would otherwise 'wear in' a bronze bearing might break a roller. Bronze bearings were certainly an option, but I decided to continue on with the rollers.

My plan for machining the rods was to cut them concurrently from a single piece of 7075. Their locations inside the workpiece would be equally distant between the top and bottom surfaces of the workpiece. The first operation was to drill and ream the four bearing holes completely through the workpiece.

I didn't have a suitable reamer for the oversize rollers, and so I used a barrel lap and Timesaver lapping compound to increase the bores from .4375" to .4390" for a .0005" interference fit which was all I was willing to chance. Since I had to lap the small end bores, I reamed the big ends a thousandth under and lapped them as well. Timesaver cuts aluminum fairly quickly, and so care had to be taken to not pass up the target. It won't embed and cause problems later, but in this application there won't be any relative motion between the fitted surfaces, anyway.

After drilling, reaming, and lapping the holes for the bearings, a trough was machined through the topside of the workpiece and down to within .100" of its bottom to define the perimeters of the rods. This allowed the rods to be completely machined except for their bottom faces which remained attached to the workpiece.

When the topside machining was completed, the troughs were filled with Devcon 5-Minute epoxy and allowed to cure overnight. This epoxy kept the rods within the troughs attached to the workpiece so it could be flipped over and the rods machined free of it. Machining the entire peripheries of the rods from the topside avoided a seam between the top and bottom side operations. The finished rods were finally removed from the workpiece by heating it to 300F and pushing them out free while still hot.

The last operation removed stock from between the tines of the fork rod in order to provide clearance for the knife rod. The bores were temporarily plugged and then the rods bead blasted to make their surfaces appear similar to those on the full-size rods. Finally, the bearings were pressed in with what felt like just the right amount of force, and the crankpins will be turned to .2515". - Terry


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## natalefr

AWESOME !


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## kvom

What's the reason for the cross slots around the bearings?

I'm currently making some parts using this Devcon epoxy, a technique I discovered from you on the radial build.  How do you get the epoxy into just the milled slots and not on the part face itself.  Also, the color of the epoxy that I got from Lowes is a pearl color when mixed, not like that in your photos.


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## mayhugh1

kvom said:


> What's the reason for the cross slots around the bearings?
> 
> I'm currently making some parts using this Devcon epoxy, a technique I discovered from you on the radial build.  How do you get the epoxy into just the milled slots and not on the part face itself.  Also, the color of the epoxy that I got from Lowes is a pearl color when mixed, not like that in your photos.



The slots are to provide an easy path for oil flow into the bearings which are open style bearings.  
I use plastic 1oml or 50 ml syringes to direct the epoxy. You can buy them by the case cheaply online.
There are two kinds of Devcon 5 minute epoxy. One is a gel which doesn't flow out as much as the regular stuff. It is a pearl color when mixed. I've used it almost exclusively in the past when I didn't have well defined troughs to fill since it was a little more efficient to use and tended to stay put a little better than the regular stuff which I used above. The regular stuff is a little more clear when mixed. It flows more easily and is more convenient to use when you have deep troughs because it will flow out and fill them more easily than the gel. I used to machine my parts half-way through each side of their workpiece and this would leave a bit of a seam that had to be cleaned up later where the two operations met. This style of machining didn't involve deep troughs and was more appropriate for the gel. After learning I could get rid of the seams by milling the entire part from one side, Instarted doing that, but I now had deep trough($) that had to be filled and for this I used the non-gel.

I think I started noticing, a year or two ago, a change in their formulations because I use to get the parts to release quickly and easily with a heat gun. Now I put them in my shop oven at 300F and, wearing oven gloves, push the parts free while they're hot. This might also be due to the fact that I've been cleaning the parts better than I used to. The non-gel stuff has less strength than the gel and so when I began using it it I started being more careful about cleaning the parts before applying it. I use Simple Green and then rinse with water and then use dish soap and hot water to clean the cutting fluids from the parts before applying the epoxy. I became anal about the cleaning after once having a close call where a part pushed free of its workpiece before heating. - Terry


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## kvom

My current experiment went a bit south.  Not having the syringe, I just covered the entire part.  Cured overnight, and then face milled the bottom to reveal the part.  After half an hour at 400F the epoxy had turned orange like your photo, and while I was able to remove the part, there was still epoxy clinging to the part (Mic6 Al) that resisted coming off (tried to slice it off with a box cutter - fail).  I put the part back in the oven a 500F for half an hour, which resulted in the epoxy turning black and adhering even worse.  Finally tried to burn it off with a torch, which got most of it off, but still spots that resist light sanding or scotch brite.  Probably bead blast would be best, but I haven't the gear.  Parts are usable but not shiny.

I'll order the syringes for the next try.


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## mayhugh1

I've never heated the stuff over 300F and so you might have baked it onto your parts. You do need to push the parts free while still hot right out of the oven. I use 'Ove Glove' oven mitts to handle the hot parts. Slopping the epoxy over the part shouldn't be a problem as the epoxy can be rubbed off the surfaces where you don't want it. If it's still sticking to your part, put it back in the oven for another ten or fifteen minutes but at only 300F, and it should rub right off.
The connecting rods above pushed right out on the first try, but there was a bit of epoxy sticking to the sides of one of the rods. While still hot I rubbed most of it off with a wood popsicle stick. There was still a bit that wouldn't come off, and so I put it back in the 300F oven for a short while and, on the second try, it rubbed right off with my gloved hand. - Terry


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## kvom

Thanks.  I ordered syringes and will remake the parts.  This is a valuable technique to master.


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## johnmcc69

Great techniques Terry, & a wonderful thread.

 John


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## mayhugh1

After making pistons by the handfuls for my other engines, it didn't feel right to make only a couple for the Knucklehead. So, I machined two for a stock 5.3 compression ratio and a second set for a slightly higher 6.5 c.r. The higher compression pistons will probably need to be notched for valve clearance, but that'll come later after the camshaft lift is determined.

If I've correctly interpreted the Draw-Tech piston drawing, it shows six equally spaced holes drilled radially through each of the three ring grooves. Many pistons have oil relief holes in their oil ring groove (along with some kind of path through the oil ring itself), but I don't understand the reason for drilling holes through the compression ring grooves.

The intent may have been to use combustion gases to pump oil into the connecting rod's small end bearing, but holes in the top groove will also leak compression and reduce the forces sealing the ring to the cylinder wall during the power stroke. And, without some kind of path through the bottom ring itself, it's not clear that holes in the bottom groove will do anything. I wasn't able to determine the rings' radial back clearances from the drawing, but the axial groove clearances specified as nominally zero also confused me. I may have misinterpreted the original design intent, but since I didn't understand it, I opted to redesign the pistons.

I started by reducing their o.d. by .003" except for the short portion inside the cylinder above the top ring which was reduced by another .003" to allow for temperature expansion. The number of rings was reduced from three to two, and an oil collection groove was added immediately below the second ring. Relief holes drilled through this groove will direct oil scraped by the lower ring into the interior of the piston. The essentially zero clearance around the connecting rod in the original design was increased to .040" on each side of the rod. The photos show a few other cosmetic changes intended to make the pistons look a little more like the full-scale versions, but it turns out there are quite a variety of them.

A couple other clearances will define the design of the rings when they are machined later. These include a .001" axial groove clearance as well as a .006" radial back clearance behind them.

The photos include CAD models of both the 'high' and low compression pistons. A cross-sectional drawing that includes the head's hemispherical combustion chamber shows a comparison of the piston dome heights inside the head at TDC.

The piston blanks were prepared by turning their finished o.d.'s to .003" less than the inside diameter of the cylinders. This is the clearance used in my radial engines, but since the heads in this engine won't be as effectively cooled (no prop wash), the piston diameter inside the cylinder above the top ring was reduced an additional .003".

With a piston blank installed in a collet block, the hole for the wrist pin was drilled and reamed before its interior was machined for the connecting rod. The blanks were then moved to the lathe where their domed tops were turned and the ring grooves cut. A chatter-free finish on the lower wall of the ring grooves is especially important because it's a sealing surface for the compression ring(s) during the power stroke. The oil relief holes will be drilled later when the mill's fourth axis is set up to machine the cam box gears.

The wrist pins, which are press-fits in the pistons, were turned from O-1 drill rod. One end of each pin (the heat darkened end in the photos) was finished a couple tenths oversize to create the interference for the fit. Before heat treatment, their ends were drilled and reamed for soft round-head aluminum rivets that will protect the cylinders from the edges of the hardened pins in case they move inside the piston. The wrist pins were oil quenched after being heated to 1475F and tempered at 350F prior to pressing in the rivets. Heat treatment was needed because the roller bearings in the small ends of the connecting rods will ride on them. - Terry


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## e.picler

Wonderful work!

As always your machining quality is amazing, as well as the photos and CAD details.
Congratulations!

Edi


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## mayhugh1

The pushrod assemblies are similar to those in the full-size engine and, with about a dozen parts each, they're fairly complex. I'm currently modeling their parts so I can build a virtual assembly and better understand the order in which they'll need to be assembled and also how lash adjustments were intended be made.

The guide blocks are the cornerstones in these assemblies. They couple the roller lifters inside the cam box to the pushrods which in turn operate the rocker arm assemblies inside the rocker boxes. The head assemblies have already been completed including the double-angled rocker access holes drilled through the bottoms of the rocker boxes.

The pushrod cover tubes are three-piece assemblies. An upper tube is expected to slide into the bottom of the rocker box, and a lower tube slides into the top of the guide block. A third tube covers the gap between them. Ideally, in each assembly, the axes of all three tubes will align with the holes in the guide block and rocker box and provide the necessary clearance around the pushrod to accommodate its changing axis while operating the rocker arm. The compound angles for each pushrod assembly are different, and poor fit-ups with the rocker boxes will create oil leaks.

The guide blocks are among the Knucklehead's most difficult parts to machine because of the precision intended for the angles of the guide holes that must be drilled through them. Errors of just a fraction of a degree will affect the fits of the parts within the assembly and create oil leaks. Many of the already completed parts affect the locations and/or orientations of the rocker access holes, and machining errors in them will also affect these alignments.

The axes of the guide block through-holes are provided in the drawings with a pair of angles (to two decimal places) and a touch-off point referenced on the bottom surface of the block. An error in a guide block angle of just a tenth of a degree will cause the cover tube assembly to miss its target in the rocker box by .005". Realistically, an error of half a degree can probably be tolerated before pushrod clearance becomes an issue. Cosmetically, the center cover tube is capable of hiding a minor mismatch between the axes of the upper and lower tubes.

Another consideration for the guide block through-holes involves the camshaft. The lobes on the stock camshaft are only .080" wide (the rollers are .064" wide), and the cam will be located approximately 1-1/2" below the guide block. This means that a 0.1 degree error in a guide block angle will move its roller contact .003" across its lobe. (Another set of angles coming up later will define the orientations of the rollers so they ride flat on the cam lobes.) Some errors can be accommodated by moving the locations of the lobes along the camshaft as needed to keep the rollers centered. However, the lobes have to remain sufficiently separated to avoid interference between their roller guides - especially those in opposing guide blocks.

A CAD model with a couple views from inside the cam box shows the relationships among the camshaft and the guide blocks using pairs of pointed test rods inserted through the guide blocks and contacting the camshaft. The guide blocks were modeled using the dimensions provided in their drawings, but they sit on top of the model of my slightly enlarged cam box. The camshaft lobes are, for now, just simple circular disks, but they are spaced as defined in the camshaft drawing. The model shows the center distances between the test rods being spot on the centers of the lobes.

The guide blocks were machined from 7075 aluminum. Each of the holes had to be spotted, drilled, and reamed in separate operations using setups that allowed the x and y tilts of the blocks to be adjusted. I used an electronic angle gauge to roughly set each axis, but the final settings had to be tuned with a z-axis dial indicator in conjunction with the mill's DROs. The angle gage was barely able to handle even a single degree of accuracy. Readings and resolution in one axis were unpredictably affected by the angle of its other axis, and so the angles had to be independently measured and adjusted.

I spent a lot of time carefully tweaking each setup, but in the end I could do no better than a tenth or two of an indicated degree. The angles invariably and unpredictably changed when the various lockdowns were tightened, and the setups generally lacked rigidity. With drill starting and wandering added into the mix, I doubt the holes ended up within a half degree of where they were supposed to be.

My biggest frustration with the setups, though, was with what seemed like never-ending confusion about which direction to tilt the axes. Working from the bottoms of the parts and with such small angles made sanity checks difficult. I had everything ready to go more than once only to discover that the entire setup was backwards. One time, after completely reversing it, I realized everything had been correct the first time. Anyone watching my clown show couldn't have helped but laugh hysterically. After nearly a full week, I had four scrapped guide blocks and a single pair of candidate block to show for my efforts.

With the finished guide blocks sitting flat on the top surfaces of the cam box, I checked them using test rods that were closely fit into the blocks but had top ends that were turned down by .010" for trial fitting into the rocker boxes. The errors were a bit too large for both test rods to enter the front rocker box, but I was able to get both into the rear rocker box.

Both guide blocks had to be moved a mysterious .045" away from the inside edge of the cam box to achieve the best overall fits of their test rods inside the rocker boxes. The eighth inch by which I radially increased the periphery of the cam box to accommodate its o-ring accounted for only .005" of this. Since both blocks were identically affected, I initially thought the difference was due to some other change that I made. The CAD models don't support this, though, and my assembly model shows the guide blocks properly located .005" from the edge of cam box. My suspicion is that there was a systematic error related to the touch-off points on the bottoms of the tilted blocks.

One of the CAD drawings shows a cam box gouge that would have been required for clearance of the roller guide in the rear intake position. This is a 'feature' of the stock design, and my CAD model predicts it should vanish as a fortuitous result of the .045" translation.

The next step would have been to transfer the 'best fit' guide block mounting hole locations to the cam box. With all the work already put into the cam box, I wanted to make sure there wasn't going to be an issue with the camshaft. I machined a test fixture consisting of a duplicate of the top-end portion of the cam box along with a dummy camshaft. Transferring the mounting hole locations to the cam box CAD model automatically transferred them to the fixture, and they became part of its machining. I added generous clearances around the expected locations of the test rods so I could duplicate the virtual camshaft test done earlier. The resulting measured spacing between the centers of the rods at their points of contact on the dummy camshaft were within .010" of their theoretical values. Their absolute distances with respect to the edge of the cam box were, on average, offset by the same .045". Fortunately, I could see no issues that couldn't be accommodated with minor camshaft modifications.

Finally, I drilled the mounting holes in the cam box and installed the guide blocks. A full length test rod was installed in one hole in each block, and a pair of half-length rods in the other. I was able to verify that a cover with an i.d. that was just .010" over the test rods' o.d.'s would slide over the pair and hide the mismatch.

The next step is to complete the modeling of the rest of the pushrod-related components and begin work on them. - Terry


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## mayhugh1

Two pairs of guide holes matching those in the guide blocks had to be drilled through the roof of the cam box. The setups weren't pretty, but they were functional and provided the reamer clearance needed under the spindle. Verifying these setups before drilling was much less confusing that those associated with the guide blocks since the blocks themselves were used as clamping guides.

After aligning the fixture plate with the mill's x-axis, its tilt along the y-axis was the only angle that had to be carefully adjusted for each hole. This angle was set equal but opposite to the one being matched in the guide block. With the guide block installed on the cam box, one end of a close fitting length of drill rod was inserted into it and the other end chucked in the spindle. The guide angle along the mill's x-axis was automatically established by the guide block, and the table needed only to be brought forward so the fixture plate could sit flush against the rear of the cam box. After clamping the two together, the guide block was removed so the hole could be spotted and drilled. The block was then replaced and a reamer run through the combination. This process was repeated three more times for the remaining holes.

When the guide hole drilling was completed, the pointed test rods used in the camshaft checking fixture were moved to the cam box. Eyeballed measurements showed the points of contact on a short length of drill rod sitting in the camshaft's approximate location looked as expected. The cam box ended up slightly gouged, after all, by the clearance hole drilled for the rear intake guide.

I needed a break from the pushrod assemblies, and so I tied up a few loose ends on the cam box. The dipstick, a magnetic drain plug, and the mounting locations for them were machined next. Both parts are o-ring'd. The drain plug was machined from 303 stainless and the dipstick's head from aluminum. The stick itself is a length of drill rod that was flame-darkened to make reading the oil level a little easier. - Terry


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## mayhugh1

While looking for an excuse to put off working on the pushrod covers for a couple more weeks, I happened to recall the drawing for the Knucklehead's oil pump. Even though it's just another gear pump, the uncommon tooth profile of its gears caught my interest.

A gear pump works by moving fluid through it in the spaces between the roots of its gear teeth and the inside walls of its close fitting housing. Pump gears have few numbers of teeth in order to maximize the volumes of these spaces. For spur gears this usually ends up being between 12 and 14 teeth.

Spur gears are widely used in oil pumps. Their involute profiles keep two or more pairs of teeth meshed at all times. This is helpful for power transfer but, in pump applications, pockets of incompressible fluid become trapped in the spaces between these teeth. The volumes of these trapped spaces continually vary as the gears rotate, and if the pump isn't totally submerged, air can be drawn into a space whose volume is decreasing.

The stresses created while trying to compress an incompressible fluid not only put strain on the pump, but they also rob power from the engine. Commercial pumps use escape grooves that direct this otherwise trapped oil into the pumps' bearings. Model engine pumps often don't include this complication since in practice they usually aren't all that well sealed.

The continuous contact tooth profile used in the Draw-Tech pump is an alternative to the involute profile. It theoretically eliminates any trapped oil and, with even fewer teeth than available from a spur gear, the transport spaces can be larger. Any real performance advantage will be affected by the accuracy of the gear machining which, unfortunately, looks like a nightmare on a manual mill.

I've included a couple models comparing the two profiles in pumps with similar size housings. The involute gears are typical 14t/24P pump gears with .667 inch o.d.'s. The Draw-Tech gears are .625 inches in diameter. The line of continuous flank contact on the Draw-Tech gears traces out a figure eight pattern and prevents oil from being trapped between the teeth. In comparison with the spur gear pump, its transport spaces are also larger.

Although mostly for its novelty, I thought I'd give the new gear profile a try. I started by turning a pair of test blanks from 932 bronze. The o.d's of their shafts and gear bodies were fully finished on the lathe, and the tiny corner fillets left behind by the lathe tooling were removed using the edge of a sharp parting tool. For the tooth profile I used the exact dimensions provided in the Knucklehead drawing. Before starting, I cut a few test slots with the end mill that I planned to use so I could account for its exact cutting diameter.

After machining the test gears, I drilled/reamed several sets of shaft holes in a test block so I could experimentally determine a proper spacing for them. I found I was able to decrease the .480" center-to-center spacing shown on the pump body drawing to .468", and still have some .004" safety margin. The gear set turned very smoothly with no tight spots even with the reduced spacing. Finally, I machined an identical set but with the proper end shafts for use in the pump housing. They behaved identically to the test gears in the test block. - Terry


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## sbdtasos

Hello Terry
excellent work as always
what is the diameter of the gears?
thanks
Tasos


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## mayhugh1

sbdtasos said:


> Hello Terry
> excellent work as always
> what is the diameter of the gears?
> thanks
> Tasos


Tasos,
Their o.d. is .625"
Terry


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## mayhugh1

Just a few more parts were needed to finish up the oil pump. In addition to the already finished pump gears, a housing and rear cover plate were needed to fully enclose them. The gear shafts pass through the front and rear faces of the pump, and so it's important that their axes remain normal to the pump's body after assembly to avoid binding the gears inside their close fitting recesses. In the original design, this alignment would be affected by the clearances around the four mounting screws that pass through the body and cover when the pump is secured to the cam box. These clearances would also affect the location of the end of the drive gear's shaft which is intended to slide into a flanged ball bearing that will be pressed into the cam box cover.

I enlarged the housing dimensioned in the drawing in order to move the mounting screws away from the edges of the gear recesses, and I also integrated the elbow for the pick-up tube into the body. But, more importantly, I added a pair of dowel pins to positively locate the rear cover to the pump body.

Construction began by facing two pieces of 360 brass to the finished thicknesses required for the pump's body and cover. Clearance holes for the pump's mounting screws were individually drilled through each workpiece. The identical hole pattern was then tapped into a sacrificial aluminum block so the two workpieces could be stacked and simultaneously machined. After drilling and reaming holes through the entire stack for a pair of dowel pins, they were pressed into place for the remainder of the machining.

With the pump's body and cover doweled together, the holes for the gear shafts were drilled and reamed through the entire stack. The peripheries of the housing and its cover were then machined together. A hole through the side of the pump, required for the inlet and outlet ports, was drilled in a separate setup before machining the gear recesses.

In order to machine the gear recesses, the cover was removed, and the center of each shaft hole was individually indicated. The diameters of the recesses were machined .003" over the o.d.'s of the gears, and each recess was verified for a proper fit with its gear while still set up in the mill. Finally, the pump body was flipped over so a thrust surface could be machined on the front of the pump for a drive gear.

An oil pick-up was fashioned from 3/16" soft drawn copper tubing and soldered to the elbow on the pump housing. Anyone familiar with the drawings might notice that I've reversed the positions of the pump's inlet and outlet. This was done since I plan to replace the Draw-Tech 'Twingle' cam with a more conventional Harley grind. In the process, the direction of the engine will be reversed so it will become the same as that of the full-size engine. As a bonus, the pump's output line won't have to be routed through the crowded area around the distributor.

Since I wanted to also add the oil pump's drive gear, I set the mill up to begin machining the engine's spur gears. I morphed the pair of short crankshaft drive gears in the original drawing to a single long gear that I machined from Stressproof.

Both internal pump gears wind up supported by integral bearings in the front and rear faces of the pump housing, and the pump's drive gear is driven by the crankshaft through a 3:2 gear set. In the original design, the drive gear's extended shaft is also expected to slip into a ball bearing pressed into the cover of the cam box. In actuality this end bearing probably provides little positive benefit, but it would complicate the assembly of the cam box to its cover. After weighing the pros and cons, I decided to shortened the shaft and leave out its end bearing.

The cam box will come on and off the crankcase many times during the machining and trial fitting of its several components. I enlarged the through-hole in the cam box for the crankshaft in order to clear the crankshaft gear so it won't have to be constantly removed as well. I also changed the method for pinning the crankshaft gear to its shaft. Since there isn't room inside the cam box to deal with the tight-fitting spring pins recommended in the drawings, I used slip-fitting solid dowels instead which are very easy to remove and re-install. Their through-holes were centered between the gear teeth and, in usage while rotating, their mating gears prevent them from moving out of place. I've found this method to be effective and very convenient for maintenance any time I'm dealing with gears with even numbers of teeth. - Terry


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## gbritnell

Hi Terry,
Excellent work as always. I understand the reasoning behind the shape of your oil pump gear teeth and the oil being trapped at the clearance area at the root of the teeth but my question is won't oil also be trapped in your version as the radius on the one tooth slowly becomes tangent to the adjacent tooth there will still be a small area that the oil gets trapped in before the teeth completely mesh? 
Yours is much like a trochoidal pump only with external gears. 
gbritnell


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## mayhugh1

George,
Thanks for your comments. I've included a photo of the one place in the gears' rotation where a compressible trap might look like it would occur, but it appears that a rear escape door opens up at the exact same time that the front door closes and so compression doesn't seem to occur. -Terry


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## mayhugh1

Tying up a few more loose ends allowed me to complete some of the engine's final assembly and continue procrastinating over the pushrod assemblies. With the fourth axis still set up under the Tormach, I drilled the oil escape holes through both sets of pistons. Each received fourteen .052" holes drilled radially through its oil groove.

A pair of TDC marks were also engraved on the rear half (flywheel side) of the crankcase. These, in conjunction with an earlier engraved TDC mark on the flywheel, will be used to time the camshaft to the crankshaft and to adjust the valves. These two crankcase marks, "F" and "R", are spaced 45 crankshaft degrees apart which, non-coincidentally, is the angle between the cylinders.

With the timing marks and crankshaft gear completed, the rear oil seal was installed, and the crankcase finally assembled with an o-ring between its halves. The nuts on either end of the tapered crankpin were Loctited and torqued to 60 in-lbs. The final crankshaft TIR, .0005" measured at the cam box cover bearing, improved slightly compared with earlier measurements. Friction added by the oil seal, though, took away the free-wheeling crankshaft that I enjoyed showing off.

With the crankshaft at a point in its rotation where the front piston was at TDC, the flywheel was installed on the crankshaft with its TDC mark aligned with the "F" mark on the crankcase. The camshaft will later be adjusted to define this point as the top of the front cylinder's power stroke. Since a V-twin's TDC can seem rather broad and difficult to precisely locate, I pinpointed it using a dial indicator on the piston since the heads weren't yet installed. For reference, while standing on the flywheel side of the engine with the front cylinder to my left, this engine will run counterclockwise which is in the same direction as the full-size engine.

If the crankshaft is then rotated 315 degrees counterclockwise (360 degrees - 45 degrees), the TDC mark on the flywheel will become aligned with the "R" mark on the crankcase. This is the angle at which the rear cylinder is at TDC in its power stroke. In order to complete a full crankshaft cycle it must be rotated another 405 degrees (360 + 45 degrees). At this angle the flywheel TDC mark will once more be aligned with the "F" mark, and the front cylinder will again be at TDC in its power stroke.

The asymmetrical plug firing angles in the crankshaft's 720 degree cycle, 315 degrees and 405 degrees, are what give the engine its characteristic sound - a sound that Harley tried unsuccessfully for six years to patent. A small annoyance is that the marks wound up on the opposite side of the engine from where all the adjustments will eventually be performed, but this was also true of the full-scale Knucklehead's flywheel marks.

A timing mark previously engraved on the flywheel 20 degrees ahead of the TDC mark will be also used with the "F" mark to adjust the static timing advance in the distributor. Being only a starting point, 20 degrees was a guess on my part since that number seems to work well with most of the model engines that I've built. Although not relevant to the model, the spark advance in the full-scale engine was closer to 30 degrees.

The next task was to fabricate an output line for the oil pump. I was able to use one of the panel mount compression fittings machined earlier for a portion of a feedthrough that vertically exits the cam box near the dipstick. A new fitting had to be machined and soldered to the output side of the oil pump, however. Although there wasn't much space available for a formed 1/8" oil line with compression fittings on each end, I was eventually able to come up with something that looked at home inside the cam box. A piece of 1/8" aluminum tig rod was used for all the trial-and-error bends before the final shape was transferred to a length of soft drawn copper tubing. Copper tubing work hardens when bent, and over-bends can be difficult to correct because the tube will tend to bend back in a slightly different (softer) location and leave an unsightly wrinkle. I typically use a deep grooved oak dowel rod as a mandrel for bending small diameter copper tubing.

With 90% of the cam box machining completed, it was time to bead blast its exterior to match the crankcase. Already drilled holes were plugged, and the interior was sealed up by clamping the box between a couple pieces of wood. After finishing its surface, the cam box was thoroughly scrubbed with hot water and dish detergent to remove any remaining glass particles.

Finally, recesses for the flanged ball bearings for the camshaft and distributor gear reducer were machined into the rear wall of the cam box and its cover so the bearing pairs could be pressed into place. Test shafts were machined to verify the bearings in the box properly aligned with those in the cover. Since the cam box wall thickness exactly matches that of the cam bearing, the recess for its flange was machined a few thousandths shallow to maintain clearance for its inner race against the crankcase. The bearing for the distributor gear reducer was much thicker, and so per the cam box drawing its flange wasn't recessed at all. Additional bearings related to the starter drivetrain will be added later once they have been determined. Since the bearings are open style ball bearings, any further cam box machining will require protective tape over them.

While preparing to bore a hole through the top of the cam box for the distributor, I realized I was going to have an interference issue between the distributor and the crankcase oil return fitting located near the front corner of the front cylinder. This area is very busy, and the drawings show what appears to be an unrealistic tubing bend underneath the fins of the front cylinder that would have been required to route an oil line to this fitting. Rather than notch the cylinder for clearance, I earlier moved this fitting out from under the fins. Unfortunately, that change has placed it under the body of the distributor which would again require some heroic tubing work. To avoid this, I relocated the fitting to the rear of the cam box which turns out to be the same location used by Draw-Tech for the original oil pump's output line. As discussed earlier, my oil pump output line exits the other end of the engine.

After trial installing the heads, I've noticed some issues coming up related to the oil return lines in the vee between the cylinders. - Terry


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## mayhugh1

The intake manifold and the oil return lines for the inner valve boxes compete for space between the cylinders. There's potential for interference between them that I wanted to clear up before burying them behind the pushrod assemblies. My original plan was to use the threaded compression fittings that I machined much earlier for the other more accessible oil lines. However, they may be a bit large for the space available between the heads and, without having the actual intake manifold to play with, it's hard to tell if there really is a problem.

The manifold is yet another challenging part of this engine. It's a four-piece stainless steel tube assembly that requires fixturing for a precise fit up during soldering. It attaches, unforgivingly, to the flanged intake ports located on the flywheel side of the heads. It also supports a cantilevered carburetor that hangs over the cam box. One of my concerns is that the carburetor/manifold assembly might be plagued with a mechanical resonance that's triggered by the engine's vibration. If so, the strengths of the solder joints will be extra important. Since the manifold is in a prominent location on the engine, it also needs to look good and not leak.

The relative orientations of the heads' port flanges were established long ago by several machining operations including the tricky compound-angled ports that were drilled through the heads. My modifications to these ports which were Loctite'd in place included floating flanges with o-rings for positive seals to the manifold. I also reduced the i.d.'s of the plenum runners from .375" to .312" for increased air/fuel velocity. This allowed the use of thicker wall tubing in the manifold for additional solder strength. With the accumulation of so many tolerance'd machining steps, though, I wasn't at all confident that my CAD model would be reliable enough for anything but a starting point for the manifold's design.

I didn't feel it would be wise to use the engine itself as a soldering fixture because of the limited access around the heads and the high temperatures (1200F) involved with silver soldering. Although my approach may seem backwards, the first task was to create a soldering fixture.

The top-end of the engine was temporarily assembled with all gaskets in place so I could compare the measured angle between the port flanges on the heads with the angle in my model. I did this by trial-and-error bending a piece of 16 gauge sheet metal until it lay perfectly flat against the faces of both flanges. Remarkably, the angle measured within a degree or two of the one in my CAD model. Based upon the model, I designed and machined first passes of the three components that make up the manifold's plenum. The two flanged tubes were then bolted up to the heads so I could trial fit the critical third part, a short connecting tube with matching mitered ends. My model resulted in that part being several thousandths too short, but I was still able to J-B Weld the three pieces together in situ on the engine. A combination of epoxy and 'rebar' inside the joints resulted in a non-functioning mock-up that fit the heads perfectly.

To create the soldering fixture, I trial-and-error bent a piece of 1/8" hot rolled steel plate until the flanges on my mocked-up manifold lay perfectly flat against it. The mock-up's flange mounting holes were carefully transferred to the plate, and a hole was drilled through its center for clearance around the carburetor connecting tube. The mock-up was once more bolted to the engine so a dummy carb tube could be J-B Welded to it at the exact angle needed to insure the carburetor will be aligned to the engine.

At this point I had a mock-up of the manifold that fit the engine and a critical part of the soldering fixture that fit the mock-up. The fixture was then bolted to a sturdy baseplate to which an angled support for the carb connecting tube was added. A spring loaded ram, added to hold the assembly together during soldering, completed the fixture.

From my updated sketches, the components of the actual manifold were then machined and assembled in the fixture. After fluxing their surfaces, I slipped thin brazing strips (cadmium bearing) designed for carbide tool inserts (McMaster-Carr #7759A11) into the joints between the four parts. The brand name of the flux used was Ultra-Flux, but it was just the common white silver soldering flux available from many sources. The assembly was heated with a MAPP gas torch, and the throw-away fixture that I spent nearly a week developing had its five seconds of fame when it pushed and held the assembly together while the solder flowed out and cooled.

The cooled assembly was pickled in sulfuric acid (drain cleaner) to remove the residual flux and then neutralized in a baking soda/water solution. After bead blasting, I noticed one the joints was slightly misaligned, but it was filled with solder and looked very acceptable. I've run into this misalignment problem before. With the ribbon sticking out from around the joint, it's difficult to judge when the parts on either side of it are precisely aligned. The soldered manifold fit the engine perfectly, though, and the carb connecting tube wound up horizontal as I had hoped. Finally, a flange for the carburetor was machined and soft soldered to the end of the carb tube.

For a better looking finish and a bit more strength, I re-heated the assembly and 'buttered' the joints with low temperature (450F) Sn/Ag solder (TM Technologies ABS-0065). After a few hours of filing and sanding, the manifold was finally finished. The imperfections that I covered up were minor, but with all the hours put into the fixture, I felt like the manifold deserved a few of its own. - Terry


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## mayhugh1

More Photos ...


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## Scott_M

Just beautiful Terry !   Like all of your builds, I am really enjoying this .
Many thanks for the time you take to document and photograph all of your setups and work. I am sure it adds considerable time to the build, I for one really appreciate it.

Scott


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## mayhugh1

Thanks for your comments, Scott.
Terry


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## mayhugh1

Spray bars inside the rocker boxes lubricate the rocker shafts with pressurized oil from the pump. Some of this oil will end up inside the valve boxes where it mustn't be allowed to accumulate and flood the valve guides - also a common source of leaks in full-size engines with aftermarket oil pumps. Four 1/8" copper lines, for which scaled compression fittings were machined earlier, drain these boxes and return their oil to the crankcase and cam box.

The two lines that drain the inner valve boxes have to be routed through the space between the heads. In the original design they were intended to be tee'd into a fitting in the center of the roof of the crankcase. The intake manifold, however, takes up a big chunk of this space leaving little room for connector'd lines. The Draw-Tech CAD renderings aren't real clear about the routing of these lines nor the design of the particular fittings associated with them. None show the manifold and oil lines together in a common view.

After installing the intake manifold, it was obvious there wasn't room for the fittings that I'd made. For these two lines I had to machine a pair of banjo fittings. One of the photos shows their component parts. Since the space inside the valve boxes is also pretty limited, I machined a notch in the end of each banjo bolt to provide a freer flowing oil entry. In order to insure the notches face upward where they will do the most good, each bolt was custom machined for its particular box so the thread orientations could be accounted for.

Earlier, I'd moved the return line for the outside front valve box from the crankcase to the the cam box because of a possible clearance issue with the front cylinder. This freed up its crankcase fitting which I was able to use for the front inner return line and therefore do away with the tee.

After finishing the inside lines, I formed and installed the return lines to the outside valve boxes as well. This time I used a piece of 1/8" diameter plumbers' solder for the trial-and-error bending/fitting which was much easier to work with than the aluminum rod stock I had been using.

After assembly, each return line was tested by filling its valve box with oil in order to make sure it was capable of draining the box in a timely manner and without leaks. The boxes drained their room temperature 40w oil in just under a minute. The oil that accumulated in the crankcase was nicely contained by the o-ring seals between the crankcase halves and between the crankcase and cam box.

The oil pump's external line was the final and most complicated leg of the engine's oil line plumbing. A copper line from a fitting installed on the top rear of the cam box feeds oil to a tee located on the engine's flywheel top side. The output lines from this tee supply oil to the spray bars through compression fittings mounted on the rear of the rocker boxes.

The tee itself was made up from 3/16" silver-soldered copper tubing since its i.d. nicely matches the o.d. of the 1/8" tubing. It took a couple tries to get an acceptable part, though, because of the 'quick and dirty' setup used to hold the parts together during soldering. The 1/8" copper lines were soft soldered to the tee with the entire assembly in place on the engine. The three joints were fluxed with activated rosin and wrapped with ringlets of low-temp solder. Although a tiny butane torch was used, the tee's small size made it difficult to simultaneously heat all three joints without one or more of the rings melting and falling away due to the radiated heat. I don't like hand feeding solder because of the extra cleanup that's usually required, but in this case I didn't have a choice.

Again, the intake manifold proved to be an obstacle, and this time it forced the routing to be unsatisfying asymmetrical. After studying photos of the routing of the lines in the full-size engines I noticed they weren't all that tidy either, though. - Terry


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## minh-thanh

You are a master of engines .
All the details of the engine are great !


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## tornitore45

Perfection even in the smallest detail.


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## johnmcc69

I'm blown away by your attention to the smallest details & engineering you're putting into this Terry. Very well executed & I just love that bead blasted finish. Just awesome!

 John


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## mayhugh1

While out of town during the past week, I managed to do some groundwork for the Knucklehead's starter. The Draw-Tech starting system was designed around a Mega AR390031 (15 turn) 540 size brushed dc motor. This is a popular and widely available motor once used in a number of cordless tools and in some RC cars and trucks. Draw-Tech designed a system of pulleys and belts to connect it to the engine's crankshaft with an effective gear ratio of about one. The BOM also calls out a 4.8 volt Li-Ion battery pack to power both the starter and ignition.

Within the same case size, manufacturers fine tune a motor's performance by varying the gage and number of turns of the wire on its armature. The AR390031 was tuned for torque. At 4.8 volts, its no-load speed is roughly 20 krpm at 1.9 amps, and its stall torque is .8 kg-cm at 38 amps.






Jameco sells the Nichibo KP5FN-3255 which is representative of what 12 volts can deliver in the same size case. Its no-load speed is 5 krpm at .2 amps, and its stall torque is 1.6 kg-cm at only 7.4 amps.

These motors can be operated anywhere on their speed-torque curve so long as attention is paid to duty cycle. Maximum output power is achieved when the motor is run with both its torque and speed at half their maximum values. The motor's recommended or nominal operating point is somewhat below this. If maximum torque is the primary goal, such as in a starter application, the motor can be run above this point and sometimes well above it for short periods of time.

The first step in selecting a candidate starter motor is to determine the engine's peak torque and cranking speed requirements. Earlier, using a torque wrench, I found that 15 inch-lbs (17 kg-cm) was required to turn the crankshaft of my Howell V-twin through its compression bumps. With nearly identical pistons, c.r., and flywheel, the Knucklehead should react similarly.

Most full-size engines require cranking speeds on the order of 200-300 rpm, and my experiences with using drill starters on model engines have been similar. Cranking speed has to primarily satisfy the needs of the engine's carburetion. A carburetor that's too large for the engine and has difficulty creating enough manifold vacuum to draw fuel at low rpms may require an excessively high cranking speed. Poorly sealing valves and/or rings in an engine with a marginally low compression ratio may also add to the requirement.

There's more to engine starting than might first be apparent, and successfully covering it with a starter spec will invariably include testing. A starter's first few revolutions are its toughest. After overcoming the flywheel's inertia and the engine's friction, the starter must then deliver its maximum torque for brief periods of time just before TDC of each cylinder's power stroke. After spin-up, stored flywheel energy may help the starter through the engine's compression bumps.

Cranking speed typically isn't constant, and this will be especially noticeable in an engine with only two cylinders. Even with flywheel assistance, an engine's cranking speed will rise and fall as its cylinder pressures change. In a twin, these peak loads will be present for less than 25% of the engine's cranking time. For once, Murphy's law doesn't apply, and the rpm rises between compression bumps will happen at just the right times to aid fuel/air flow.

Based upon the above, I've chosen for my target a conservative 25 kg-cm at 300 rpm at the Knucklehead's crankshaft. This works out to be about 75 watts of peak mechanical power. The AR390031 is far from being able to deliver such power without help from a gearbox. Gearing has the effect of changing the slope of the motor's speed/torque curve. Its no-load output rpm will be reduced, and its stall torque increased by the gear factor. For example, if the the 4.8 volt motor's output shaft is geared down by 40, its stall torque will increase to 32 kg-cm, and its no-load speed will drop to 500 rpm.






With gearing, this motor would meet my requirements but with a pretty high current draw due to its low operating voltage. As a result, I also decided to run the entire engine from a 12 volt battery. A gear ratio of 40 will require a large number of gears for the space available, though, as well as a one-way clutch to prevent the engine from trying to reverse drive the gear set after it starts.

Gear motors are available from a number of sources. They efficiently pack gear boxes inside an extension to the motor's head without increasing the diameter of its case. Robotics suppliers are good sources for these because they include torque numbers in their specifications which is something RC suppliers don't do.

An example of a gear motor that should meet the Knucklehead's requirements is:

https://www.servocity.com/313-rpm-hd-premium-planetary-gear-motor

Its basic 12 volt motor has a no-load speed of 8.5 krpm at .52 amps and a stall torque of 1.1 kg-cm at 20 amps. With its 27:1 internal gearing, its no load rpm drops to 313 rpm and its stall torque jumps to a whopping 30 kg-cm at 20 amps.






There are many 'similar' gear motors available on eBay and Amazon at much lower cost, but in many cases their torques aren't specified. Several of these are sold as 'high torque' but don't contain enough copper for this application.

Another source for useable motors and gear boxes are battery-powered drills. A real advantage to using them is that their 'good' parts can be cannibalized after testing them in a still convenient form factor. An example is the Black & Decker BDCDD12C 12 volt 550 rpm cordless drill which is widely available for about $30. Although removing the chuck can be a bit tricky, these tools are easily to disassemble, and a number of Youtube videos are available to help. Their dual planetary gear sets can save a lot of work even if a suitable housing has to be machined.

While still on the road, I placed an online order for one of the ServoCity gear motors. I plan to run some tests on it using my Howell V-twin as a mule before trying to design it into the Knucklehead. - Terry


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## petertha

This is good stuff, Terry. I was not aware of the servo-city type geared motor availability. The gear ratio is quite high (27:1) compared to my RC experience of planetary drive inrunners, usually in the 5-7 : 1. Is the servocity a parallel double or triple reduction type train do you happen to know? Anyway, that looks well suited to the purpose.

I just assumed (but maybe I'm wrong) the majority of variable speed drill motors are brushless. If so, there may be other considerations.
1) The nominal voltage may be different, anywhere from 9.x volts to 20 volts depending based on the cell type & chemistry used in the tool. So you would either have to replicate that by also harvesting the pack or just ensure your intended power supply is suitably matched at discharge load. Your graphs illustrate this perfectly.
2) if truly brushless (3 wire vs 2 wire for likely identification), then I assume you would also have to extract the ESC (electronic speed control) module because it is delivering commutative voltage. This could also be an advantage if you desired variable speed, but I'm not actually sure how that would be implemented.
3) The current levels you are talking about probably wont factor into excess demands on the battery. But another factor to consider for motor matching particularly using smaller cells or portable packs is C-rating of the battery itself. Just an arbitrary example, if you have a 12 volt pack made up of 10C rated cells of say 2000maH capacity, then max current = 10 * 2.0 = 20 amps. Its not a hard number but basically the voltage will sag or harder on cells. Motorcycle type batteries refer to cold cranking amps, but I believe different standard again. Current while maintaining some suppressed voltage, like 7.x volts on a 12v nominal. Anyway, at your low anticipated current should be no worries.


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## mayhugh1

Peter,
I don't know for sure what the gear reducer is in the ServoCity gear motor, but my guess is that it's a dual planetary gear set like the one in the Black&Decker drill.

I believe you're right that cordless tools are going to brushless motors, but the Black&Decker mentioned above is definitely a brush motor and maybe one of the few remaining with brushes. Most of those tools are also going away from 12 volts and are already at 18V and higher.

My plan for the battery is to use the 12V 7AH sealed lead acid battery I used on my Merlin. It delivered some 80 amps to the starter on that engine.

Thanks for the interest and comments. - Terry


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## Maxine

Awesome build.  Thank you for posting.  It is inspiring me to develop my skills further.


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## rodue

mayhugh1 said:


> After completing the Quarter Scale Merlin, I took several months off to work on a number of projects that had piled up around the home and shop. High on my to-do list was assembling a number of backup XP computers while the parts were still readily available. I've had an ongoing concern that my ten year old homemade shop computers as well as those running my wife's embroidery machines have been living on borrowed time. I could, if necessary, convert my Tormach to Linux-based PathPilot, but the hardware associated with my Wabeco lathe is still tied to Mach3. I also built up a couple Windows 7 machines so I could have at least one foot inside the modern world. I tried migrating to Windows 7 entirely, but I wasn't able to get some of my ancient CAD/CAM software nor my wife's embroidery software running on their 64-bit operating systems even in their so-called compatibility mode. Replacing all that software was pretty much off the table for me.
> 
> Committing to a new long term engine project involved a lot of procrastination and eventually came down to a decision between Ron Colonna's 270 Offy and Draw-Tech's Knucklehead. In order to shake the bugs out of the new shop computers, I modeled the Offy's crankcase as well as the Knucklehead's cylinder head assemblies in SolidWorks. I felt the Offy would probably be of wider interest to others since I'm not aware of any detailed published builds for it. In the end though I felt like I needed more time to consider some alternate approaches to the Offy's one-piece crankcase, and so for now I chose the Knucklehead.
> 
> I really liked the looks of Draw-Tech's CAD rendered Knucklehead but wasn't even aware of its existence until I came across Steve (Driller1432)'s HMEM thread:
> 
> http://www.homemodelenginemachinist.com/showthread.php?t=24705
> http://www.homemodelenginemachinist.com/showthread.php?p=301687#post301687
> 
> His successful build validated the plan set and proved the model could be made to run using the original Harley timing. So I decided to do a thread on its build and, along the way, fill in some of the machining steps that Steve left out to perhaps encourage others to build one of their own. There was so much effort put into that engine's drawings that it seems a shame to allow them to languish on the forum's download site.
> 
> Even though it has only two cylinders, this engine isn't a beginner's project, though. It's considerably more complex than a Hoglet or even Jerry Howell's V-twin, but the finished result will be more reminiscent of an actual full-size engine.
> 
> I decided to begin the build by machining the exterior components of the head assemblies which I had already modeled. This included the heads, cam brackets, valve boxes, and rocker arm boxes. At first glance, the head assemblies appear to be the most complex parts of the engine, and their individual parts must fit precisely together.
> 
> My first step was to get hard copies of the pertinent downloaded pdfs since I've never been comfortable with working directly from drawings on a computer screen.
> 
> http://www.homemodelenginemachinist.com/downloads/draw-tech-297.html
> 
> Because some of the key drawings were intended for E-size sheets, I dropped a flash drive off at our local copier store so they could print them out for me on their huge cut sheet printer while I ran some errands. When I returned, though, I was informed that the store's policy was to not copy or print out copyrighted material. They pointed out the title blocks in the lower right hand corner of the drawings that contained words to the effect that the drawings were not to be reproduced without written consent from the original owner. No amount of common sense reasoning could get me past the clerk I was dealing with. Instead of coming back later when someone a little less literal might be on shift, I printed the large size drawings out in poster board mode on my home printer and then carefully taped them together to create the large sheets.
> 
> It'll feel good to be making chips again, but with only two cylinders to deal with this time there won't be as many of them. -Terry


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## rodue

I don't have a CNC mill so I am doing a lot of hand work. I have a question and maybe you showed it on the gear box, the length  crank shaft and the a picture of the gears arrangement  I made patterns and cast the gear box and cover


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## mayhugh1

Rodue,
Have you looked through the Draw-Tech .zip download named gear-system? It contains all the gear information, but you will have to use the dimensions in the cam box drawings to locate their shafts. I've not gotten that far with mine, and so the only photos I've posted are of the drive gear for the oil pump. I'll soon be working on the starter gearing, but I'll probably end up doing something different from the original plans that may not apply to your build. - Terry


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## mayhugh1

The ServoCity gear motor arrived, but I evidently entered the wrong part number and received a 437 rpm motor instead of the 313 rpm motor that I wanted. The two motors are actually identical except for a small difference in gearing that adds another 8 kg-cm of stall torque to the slower motor. I machined a simple adapter for use between its 6 mm D-shaft and a 3/8" drive socket so I could test it by spinning the crankshaft in my Howell V-twin while holding the motor in my hand.

For my first test, I used an analog ammeter to monitor the motor's average current draw and an optical tach to measure the cranking speed. The ammeter's needle momentarily kicked up to about 9 or 10 amps at the start of each test before settling down and oscillating between 3 and 4 amps during cranking. The tach indicated a steady cranking speed of some 400 rpm.

In order to see the detail in the current waveform, I borrowed an oscilloscope with an accessory current probe. I've included a photo of a typical current waveform acquired over a two second cranking period. At the start of cranking, before the motor has overcome the rotational inertia of the flywheel, there is a 14 amp spike. This inrush is the motor's stall current as measured in my setup. My wiring resistance was on the order of a quarter ohm, otherwise this spike would have reached 20 amps which is the motor's advertised stall current.

During the next 125 ms, while overcoming the flywheel's angular momentum but before full spin-up, the motor ran into its first compression bump. Sometime after spin-up the current dropped to about 4 amps. The current continued to briefly spike up to some 9 amps at the peak of each succeeding compression bump. Two crankshaft revolutions are required to complete the engine's 4-stroke cycle, and the recording shows that the time to accomplish this was 300 ms which works out to be 400 rpm. Between compression bumps the current fell to 2 to 3 amps which corresponds to the torque supplied by the motor to overcome the engine's frictional losses and to replenish the flywheel's energy.

The instantaneous torque supplied by the motor at any time can be found using the current curve on its speed-torque diagram shown in the next photo. The 9 amp peak currents at the compression bumps correspond to about 9 kg-cm of peak torque. My earlier torque wrench measurements predicted this torque would be nearly twice this value at 17 kg-cm. The discrepancy is due to the flywheel dumping its energy into the crankshaft at the compression bumps rather than slowing down. Its energy is replenished in between the bumps.

The speed-torque diagram shows the average cranking speed is dominated by the relatively long periods of time during which the motor is in between compression bumps. If more cylinders were added to the engine, the average cranking speed would fall because the motor would spend more of its time dealing with compression.

Although I seem to have lucked out, after seeing the current waveform I was probably too focused on the compression bumps when coming up with the starter motor's torque spec. The flywheel's momentum can be just as important during spin-up, especially in a two cylinder model engine where the flywheel tends to be relatively massive. The current waveform shows this particular motor was within a couple amps of its stall current when it ran into its first compression bump only 50 ms into spin-up. The 313 rpm motor will have some additional torque available during this initial start-up time. I plan to use this motor while continuing on with the starting system's mechanical design, but I'll likely re-order the 313 rpm motor. - Terry


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## petertha

This is very enlightening sizing information. So if this approach was applied to your radial engines, do you think its fair to say negligible flywheel effect from the prop & focus on the compression bump + whatever desired headroom?

I've always wondered if starter rpm in itself makes for better or worse fire-up conditions. I have nothing to base this on other than RC engines. With fading starter motor (low rpms even though its managing to turn the crank) engine just seems to take its time to pop over faster turning starters all things equal. Maybe that's a function of timing? Example 10% of a 4000 rpm motor = 400 rpm, but 400 rpm on a 20,000 rpm motor is only 2%. Sorry for the tangent. The things we rarely think about :/


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## tornitore45

"I've always wondered if starter rpm in itself makes for better or worse fire-up conditions"
I would say not.   In my the model airplanes times,  we used to start even worn engines with a flick of the finger.  At old engine shows I have seen starting hit and miss engines by hand turning the flywheel at speed much lower than normal operating speed.
As long as the piston velocity is sufficient to make the leakage effect on compression negligible the engine should start.  The flywheel helps but the explosion/compression energy is much greater than the flywheel stored energy as witnessed by the fact that an hit and miss engine will get the flywheel spinning up with the firs firing.


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## Shipdisturber

To say this is impressive is short changing this build. Perfection would be closer.


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## mayhugh1

Sorry to be late answering, but my wife and I are dealing with incredible sinus infections, and my mind is still like a dusty dark attic. I was afraid that we might have kicked off the flu season for central Texas, but the doctors say no, our flu shots are working.

Peter,
The huge (18"-24") props on those radials (and the Merlin) have quite a bit of angular momemtum of their own. I've never done any calculations, but I just went over into the shop to spin a spare similar-size prop in my hand, and it felt very much like the Knucklehead's flywheel. I'll probably include the effects of the flywheel next time.

As far as cranking speed is concerned, Mauro, I think we'll have to agree to disagree on this one. The old 12v drill I initially used on my 18-cylinder radial had barely enough torque to turn that engine over, and wouldn't start it. After a Dah... moment (actually much longer than a single Dah),  I realized the drill had an alternate torque setting. Changing it helped a little, and the engine eventually started. I replaced the drill with an 18v version and after final tuning it still took a 2-3 seconds of cranking at 300 rpm to start a cold engine.

That said, though, as I mentioned earlier, it has to do a lot with the engine's carburetion. In both the radials and the Merlin the fuel reaches the cylinders through a long contorted path through the diffusers and intake runners. The starter needs to spin fast enough to create enough vacuum and for long enough to get the fuel in there.
I've had to crank every non-fuel-injected full-size car I've owned for a few seconds to start, and even longer on cold mornings. My fuel-injected puck-up with its built-in help getting fuel to the cylinders still requires a second or so.
I can see why simple one cylinder engines with little or no intake manifold to deal with can start much quicker. I think the guys hand starting those small RC engines also frequently have to prime them.

Thanks all for your thoughts and comments. - Terry


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## Buchanan

Would the slight rise in temperature due to compression have  a crank speed factor. More so on small engines. Temperature would be lost through the cylinder walls, piston and head, but that does not explain why a small engine is sometimes harder to start when warm.


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## Ghosty

Buchanan said:


> Would the slight rise in temperature due to compression have  a crank speed factor. More so on small engines. Temperature would be lost through the cylinder walls, piston and head, but that does not explain why a small engine is sometimes harder to start when warm.


One or two thou in a full sized engine between cold and hot is not that much of a problem, in our small engines it is the difference between a runner and not.  We can scale down engines but things like thermodynamics don't scale down the same, the same with drag and momentum.
Cheers
Andrew


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## tornitore45

Terry I do not entirely disagree, the length of intake duct and air velocity is a valid consideration.  My point was that compression as defined by fit and leakage is affected by the speed of the piston.  As long as the piston moves fast enough to make leakage negligible, compression is not lost.


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## mayhugh1

I didn't do myself any favors by getting so far into this build without having a design for a working starter system. There isn't much space available, and the gear motor I've chosen will now require a rather elaborate oil sealed adapter to get it into the cam box. The shaft's location requires a system of belts or chains in order to drive the crankshaft. Draw-Tech had pretty much same issue which they solved with timing belts and pulleys. Several of the parts shown in the drawings are non-stocked long lead items, and so I decided instead to machine a set of sprockets and use the short piece of 3/16" roller chain left over from my Merlin build.

A gear motor requires a clutch, and for that I used an RCB-06014 one-way bearing that I had on hand. Its 56 kg-cm torque capacity should easily handle the Knucklehead's requirements. There's no space available on the crankshaft for a starter drive and so, as in the Draw-Tech design, the distributor drive shaft will be driven instead. Since the distributor runs at half the speed of the crankshaft, the starter motor's shaft sprocket was sized for an approximate 1:1 effective gear ratio between the starter and the crankshaft.

Machinist Mate 4.2 http://www.wadeproco.com/ was used to design the sprockets. A single sprocket tooth profile, defined in Machinery's Handbook, consist of five curves and two straight line segments and is a tedious and error prone construction. While shoehorning the Knucklehead's chain drives into the available space inside the cam box, I found that being able to quickly create accurate sprockets for trial-and-error placement was invaluable. I experimented with several online tools and compromise construction techniques which I used to generate sprocket models for comparison with a known accurate profile used in my Merlin's cam drive. The Machinist Mate program gave the best results by far. This program accepts the chain pitch, roller diameter, and number of teeth and outputs a single tooth profile as a dxf file. Its files easily imported into SolidWorks 2010 which I used to create the sprockets. The entire process from tooth specification to completed CAD model was less than a minute.

Another helpful design tool was one that calculated the number of chain links required for a particular center-to-center sprocket spacing. I used a pair of free online spreadsheets:

https://www.chiefdelphi.com/forums/attachment.php?attachmentid=11180&d=1323635128

One spreadsheet uses the chain pitch, the numbers of teeth on each sprocket, and a desired center-to-center spacing in order to calculate the number of required links including any partials. A second sheet uses the pitch, tooth counts, and number of desired whole links to calculate an exact center-to-center spacing. Since I didn't have room for tensioners, I was concerned about the margin built into the calculations. I tested the second spreadsheet using a pair of machined sprockets that I created using Machinist Mate and found the fit to be very acceptable. I learned the hard way, though, that because of the connector link design only even numbers of links are usable. This, in addition to my very short and irreplaceable chain remnant, were painful restrictions.

After completing the designs of the chain drives (with three links to spare) CAD models for the remaining components were created. The photos show the finished model of the starting system. For simplicity, only the cam box components directly associated with the starter or its clearances are shown. My ancient version of SolidWorks doesn't have the ability to functionally play with roller chains, and so I didn't expend the effort to just cosmetically add them. Clearances around the chains and connector links were major considerations though. In the photos, paired sprockets are identified using identical colors.

There seem to be differences of opinions about the minimum number (6-10) of teeth recommended on a sprocket. Since I was interested in conserving links as well as making the motor shaft sprocket as small as possible, I ran my own tests. I found that an eight tooth sprocket didn't seem to like my 3/16" pitch connector links as much as a nine tooth sprocket did, and so I selected nine teeth as my usable minimum.

In order to make sure that I have an actual working design before doing the final machining on the cam box, the next step will be to machine the starter components and assemble them into a starter that I can bench test on a mock-up plate. - Terry


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## kvom

I was out of the country the past 3 weeks.  Your progress during that time made for a delightful early morning read.


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## mayhugh1

The motor adapter was machined from aluminum for a snug fit around the ServoCity series of HD planetary gear motors:
https://www.servocity.com/motors-ac...uty-gear-motors/premium-planetary-gear-motors
The motor I'm currently using is the 313 RPM version that I previously tested using my Howell V-twin as a load. Its gear-case makes the motor a little longer than I'd like, and so I'm using the adapter to hide some of it inside the cam box. The adapter was machined for a shaft seal, and a .010" teflon gasket between it and the cam box should prevent oil leaks.

The motor sprocket was machined from 1144 to closely fit the 6 mm D-shaft. There's a hub for a grub screw, and between it and the sprocket is a clearance groove for the chain. One of the issues that I wrestled with during the design was providing enough clearance around the chains for the connector links which are somewhat wider than the chains themselves. Space around the sprockets is so tight that some of those clearances are only .010".

The primary chain connects the motor to an over-running clutch. The clutch is actually an RCB-06014 one-way bearing running on a countershaft located between the motor and distributor drive shaft. Its exact location had to satisfy the 'whole link' requirements of both chains and in doing so influenced the sizes of all four sprockets. The result compromised the 1:1 effective gear ratio that I was trying to maintain between the motor and the crankshaft. I ended up at 1:1.2 which reduced the available torque at the crankshaft by 20%. I had been toying with the idea of replacing the 313 RPM motor with the 437 RPM version, but now seems counterproductive. A 165 RPM version with twice the torque is available if necessary.

Although the countershaft has its own sprocket and spins on its own pair of end bearings, it's also the inner race of the one-way bearing. During starting, the countershaft is locked by the clutch to the starter motor through the primary chain. When the engine starts, the secondary chain linking the distributor drive shaft to the countershaft over-runs the starter and the clutch disengages it.

The sprocketed countershaft was also machined from 1144. Manufacturers recommend hardening the inner shafts used in one-way bearings, but I was concerned about my ability to correct any warpage that might be created by the heat treatment. Instead, I decided to rely upon Stressproof's extremely high tensile and yield strengths to withstand the bearing's sprags without deforming. Although it's not a guarantee that 1144 is up to the task, I've been running this same bearing inside the Merlin on a similar shaft with no issues so far. Inside the Knucklehead it will be running at less than half its rated torque.

A one-way bearing has a thin drawn outer shell that requires a pressed-on backup sleeve. If the shell's o.d. is measured, it may appear to be a couple thousandths oversize and out-of-round. Regardless, it's important that the i.d. of its pressed-on sleeve be exactly that specified by the manufacturer. It's also advisable to use an arbor similar to the one in the photo during the pressing operation in order to support the bearing's internals against damage. It's easy to become confused about the bearing's direction, and over time I've learned to check twice and press once. My particular sleeve including its integral sprocket required the full capacity of a two ton manual press.

The distributor drive shaft is geared to the crankshaft, but it's also linked to the countershaft through the secondary chain. In addition to its integral sprocket, this shaft contains additional features for mounting the crankshaft-to-distributor reduction gear as well as a miter gear for driving the distributor. The reduction gear is bolted to a flange on the shaft, but the miter gear's hub will be inserted into a recess machined into a rear face on the shaft. The miter gear will be Loctited in place after the distributor is completed and the gear's exact location on the shaft can be determined. This recess was machined using a tiny face grooving tool ground from a .042" HSS drill bit that I soft-soldered to the end of a piece of steel.

My confidence in the design grew while machining its components, and so I decided to scrap the idea of a trial assembly on a mock-up plate. Instead, I finished the cam box machining and assembled the starter inside it.

It was a great relief to find that the shafts lined up properly between the cam box and its cover. The cover is doweled to the cam box, all the bearings are snug press fits, and the shafts are close fits inside their bearings; and so there was little room for error. Once the alignments were verified, I fine-tuned the lengths of the shafts for a .003" thrust clearance while keeping the paired sprockets at the same height. The chains appeared to have the proper fits, and they ran interference-free with the cover in place. I was disappointed, though, when I realized I wasn't going to be able to watch them running. The sprocketed shafts require the support of their outer bearings, and the starter can only be safely run with the cover in place.

Additional good news was that I somehow managed to properly install the clutch. The flywheel spins in the correct direction when the motor is energized and freewheels when it isn't. Since the engine isn't far enough along to build compression, the only load I could put on the starter was my uncalibrated hand on the flywheel. The starter sounds good though and has a whine that's reminiscent of a full-size engine. - Terry


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## kvom

How did you cut the teflon gaskets?  I've been using an xacto knife.  I like the drill fixture.  I've been using a manual punch that is likely less accurate.

I must have missed what the purpose of the miter gear is.


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## mayhugh1

Kvom,
I cut the gaskets using a drag knife on my Tormach. I should have taken a picture of that step, but I forgot. It was just a matter of taping the teflon down to a sacrificial surface under the spindle and cutting a pair of circles. The 2-56 holes were too small for the knife, and so I stacked a few gaskets and drilled through them using the fixture shown.

The miter gear is for the distributor that still has to be made. It will sit on the roof of the cam box and protrude down inside it. Its shaft will have a matching miter gear on it so it can be driven by what I've been calling the distributor drive shaft. The distributor drive shaft is geared down from the crankshaft by 2:1 and the 1:1 miter gear set will ultimately spin the distributor at half the speed of the crankshaft. - Terry


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## mayhugh1

A final addition to the starter was a cosmetic cover for the motor. It was turned and polished from a chunk of 1-3/4" diameter aluminum and then machined with cutouts for the battery terminals. I covered up the air vents over the brushes in order to keep exhaust grunge out of the motor. Hopefully the motor will never have to be run long enough to overheat. Clearance slots for the adapter's mounting bolts allow the cover to slip over the motor and completely enclose it.

Large permanent magnet dc motors often have an external spring clip over the outside of their housing to shunt any residual flux from the stator magnets. The low permeability path provided by this steel sleeve reduces nuisance external magnetic fields and provides a small torque improvement by increasing the flux density in the motor's air gap. My interest was in sleeve's inherent springiness which I used to keep the cover in place.

I didn't end up with the final gear ratio that I had been assuming during the design of the starter, and so I ordered the 165 rpm version of the motor as a backup. It spins the crankshaft at 200 rpm and provides plenty of torque. Unfortunately, it has an even longer gear box and requires its own cover. I wanted to move on to the distributor and be done with the starter, and so I also machined a cover for this motor while the fixtures and the setups were still fresh in my mind. With this motor spinning the engine, it's nearly impossible to hold onto the flywheel. - Terry


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## mayhugh1

The Knucklehead's distributor is something of a misnomer because it really doesn't distribute anything. It has a rotor that opens and closes a set of points or, in my case, triggers a Hall device; but the plug voltages aren't brought inside the distributor. Not having a high voltage section greatly simplifies the design, and the Hall sensor catches a big break. As in the full-size engine, each plug will be connected directly to its own coil, and the trigger will simultaneously fire them both.

This 'wasted spark' or 'dual-fire' system is used today in modern distributor-less automotive ignitions. In even-firing engines there's no adverse effects because the cylinders can be paired so the wasted spark always occurs on an exhaust stroke. This isn't quite the case with uneven-firing Harleys, however.

In a Harley engine the rear cylinder is ahead of the front cylinder by 45 degrees which is the angle of the engine's V. Initially, assume zero spark advance. When the rear cylinder fires at TDC, the front cylinder will be in its exhaust cycle and 45 degrees before its TDC. This cylinder's wasted spark causes no problems so long as the burn from the previous cycle was complete. However, when the front cylinder fires, the rear cylinder will be in its intake stroke and 45 degrees past its TDC. If conditions are right (long duration cam and/or overly-rich carburetor) there could already be a combustible mixture in the rear cylinder, and its wasted spark could create a backfire through the carburetor. Fortunately, timing advance helps to mitigate this. With 30 degrees of advance, the rear cylinder will still be in its intake stroke but only 15 degrees after TDC. It's still possible, however, for exhaust gas to suck in enough fuel to be combustible due to cam overlap. In any event, Harley switched their ignitions from dual-fire (wasted spark) to single fire in 1999 even though the aftermarket had already been offering them for several years. As an aside, that rear cylinder takes even more punishment by not receiving the same amount cooling that the front cylinder enjoys. Anyway, back to the Knucklehead's distributor ...

I reduced the diameter of the distributor from one inch to 0.8 inch because of clearance issues with that pesky oil fitting at the front corner of the front cylinder. I also reduced its main body height to clear the front cylinder's intake fitting so the distributor could be installed or removed without major engine disassembly.

Although distributors are typically negligible loads on the gear trains driving them, the 48 pitch 18 tooth brass miter set specified in the drawings seemed a bit lightweight to handle the original distributor's sleeve bearing'd rotor shaft. Just in case, I changed the design so the rotor shaft runs in ball bearings.

Because the camshaft will be redesigned, the rotor was modified to accommodate the reversal in the crankshaft's direction as well as the conversion to the 315/405 degree firing angles that the engine is famously known for. Looking down on the top of the distributor, the rotor will now spin clockwise, and its second trigger will be located 315/2 = 157.5 CCW degrees behind the first.

I decided to use an aperture disk to trigger the Hall device rather than multiple magnets. I've used both methods in the past but felt like I got better cylinder-to-cylinder consistency with the single magnet approach. Before finally deciding, I tried to compare the relative trigger distances among a number of supposedly identical magnets that I had on hand using an admittedly crude test setup. I could easily see up to .010" differences in the turn-on distances of my test Hall device which would translate to 5 (crankshaft) degree timing errors in my little distributor. The differences in the distances needed to turn the device back off (this is the trigger edge I actually use) was smaller, though.

I decided upon an Infineon TLE4905 Hall device (obsolete, but still available from digikey.com) and a stacked pair of 1/16" diameter magnets as a flux source. Bench experiments and some trial disk machining were done to derive the specs for the disk. I eventually settled on a .020" thick 12L14 disk with .125" diameter holes rotating over the center of the Infineon device. The total gap between the magnet and the sensor's face will be .035".

For an ignition, I plan to use the twin CDI unit from cncengines.com. I emailed Roy and was assured that this new style potted unit contains two separate coils and a 2X storage capacitor. This means each plug will receive the same energy that would have been available from a pair of his conventional single coil modules.

I've included photos of the CAD models showing the components of the redesigned distributor. A strain relief for the Hall sensor cable that will pass my 'tug' test still needs a little work before I start making chips. - Terry


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## mayhugh1

The distributor components were machined according to the dimensions behind the previous CAD models, and assembly went pretty much as expected. If I were to do it all over again, though, I'd use 303 stainless instead of aluminum for the distributor body. The fit of the distributor inside its bore in the aluminum cam box is snug, and even with a bit of oil, I think about galling. An extra .015" material was left on the lower end of the distributor body, the rotor shaft, and the miter gear hub. During assembly these were trimmed as needed to fine tune the mesh between the distributor's driven gear and its driving gear inside the cam box.

I tried using Loctite 680 bearing retainer to secure the magnet pair inside their recess, but even after three attempts it refused to set up. It's possible the chemistry behind the curing process is affected by magnetism. Although I don't know if they're necessary, I learned later that Loctite has adhesives specifically formulated for use around magnets. A drop of super glue seemed to work, but I top-coated the around and up to the magnet with a thin layer of JB Weld for good measure.

The mount for the Hall sensor was machined from PVC so the JB Weld used to bond the two would have some bite. A less rigid adhesive like GOOP might have been a safer choice for use over the device's sealed leads. I liked the idea of using JB Weld, though, since its metallic filler might provide some electrostatic protection.

Some careful soldering was required to attach the three 30 AWG insulated wires used to make up the sensor cable. The joints were carefully covered with JB Weld to insulate and keep them separated from one another. A piece of heat shrink tubing was embedded in the epoxy for strain relief, and the entire junction will eventually be hidden in a machined pocket in the distributor cover. The far end of the cable was terminated in a Futaba male servo connector. Since there was some technique involved with mounting and cabling the sensor, I made up some spares while the process was still fresh in my mind. I ended up modifying my design for the distributor cover shown in the earlier CAD drawings in order to provide a nicer exit for the sensor cable.

I received an email this week asking how a Hall device could possibly detect the presence of a magnet through a hole in a steel disk when the hole is only a bit larger than the magnet itself. It was a good question because one would expect the disk to capture nearly all the flux leaving the north pole at the rear of the magnet. On its way back to the south pole at the front of the magnet, the flux would just be channeled through the disk and around the hole. The disk, even with its hole, provides a low reluctance path compared with the surrounding air, and so one would expect very little flux in the air above the disk.

Modern Hall sensors, however, contain internal flux concentrators in order to improve their sensitivities. Although its design is often proprietary, the concentrator is essentially a low reluctance path integrated into the packaging and used to optimally channel flux through the sweet spot of the sensor. In doing so, it offers an alternate path to the magnet's flux while the sensor is over the hole. With the right size hole and sensor spacing it can offer an even lower reluctance path than the disk and draw some of the flux out of the hole. - Terry


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## mayhugh1

More Photos ...


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## Scott_M

Hi Terry
Beautiful work as always !  I really liked the nice job you did with the JB Weld. The connection looks very well terminated. Did you mold it or shape it while it was still soft ?  It looks really good.
Did you use the regular JB Weld or the new fast curing stuff ?
And thanks for the match sticks, that tells all. 


Scott


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## mayhugh1

Scott,
Thanks. I just used regular JB Weld and dabbed in on with a toothpick under a magnifying glass. Gravity took care of the rest. - Terry


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## Buchanan

Terry. 
The way you make the distrubter blend into the overall design is perfect.


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## XD351

That is brilliant !


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## mayhugh1

Although it was probably a little premature, my next step in the build was to fabricate a set of drag pipes for the engine's exhaust. These were formed from half inch diameter 316 stainless tubing using a Rigid three-roller tubing bender. Although I received mine several years ago as a Christmas gift, I noticed this bender (along with most everything else nowadays) is available through Amazon:

https://www.amazon.com/dp/B008ULY74G/?tag=skimlinks_replacement-20

The rear pipe was simple and easily formed, but it took three tries to get a matching front pipe.

The exhaust ports on the heads are terminated in floating o-ring'd flanges that require matching header flanges on the exhaust pipes. These were machined as separate items and then silver-soldered onto the ends of the formed tubes. For joint strength, my approach was to insert the tube into a close-fitting recess in the flange and then coax molten solder to wick up between them. Since the clearances between the tubes and the heads of the flange screws will be minimal, it was important to not end up with an interfering solder fillet. In what turned out to be a lame and totally unnecessary attempt to prevent this, I blackened the flange surfaces with a Sharpie pen as I often do when low temperature soldering. I'm certain the coating vaporized long before the melting point of the solder was reached.

For solder, I used .030" Silvaloy 355 wire (available from Brownells) and white fluoride flux. This wire has the stiffness of spring wire, and a short piece was used to form a tight fitting ring inside a recess partially bored through each flange. The diameter of the recess was .005" over that of the tube and provided the necessary capillary space between the two. The ring as well as the tube's o.d. were coated with flux and the assembly setup on a thin steel plate so the flange could be indirectly heated from below with a torch. This prevented the flux from becoming scorched before the solder reached its melting point. At just the right time, the torch was moved above the plate and splayed around the tube in order to draw the solder upward. After cooling, the baked-on flux was removed by pickling the assembly in sulphuric acid (drain cleaner from a local builder's supply). Neutralization in a baking soda/water solution followed by a thorough water rinse completed the job.

After finishing the pipes, I began having second thoughts about using (even hard) Viton o-rings in between the exhaust flanges. I wasn't concerned about the exhaust heat so much as I was about the weight of the pipes. The floating flanges greatly simplified the drilling of the screw holes around the header flanges, but the friction provided by the compressed o-rings is all that prevents the pipes from rotating on the heads' exhaust ports. This friction is holding the pipes in place now, but the engine's vibration might create problems later. I considered adding a clamp to hold the ends of the pipes together, but I wasn't sure I liked the added clutter.

Instead, I made up a Plan-B set of copper o-rings that I turned from a piece of a discarded electrode from a spot welder. In order to improve their sealing ability, I turned a .010" deep face groove around the center of both faces of each o-ring. This divided their flat faces into two .020" wide rings which will increase the effective pressure available from the flange screws. After completing their machining, the o-rings were annealed to improve their conformity to the surfaces of the flanges.

Finally, the pipes were polished using 400, 600 and 1000 grit papers followed by buffing with red jewelers rouge. The complex reflective surfaces nicely hide imperfections left behind by the bender that weren't removed by sanding. - Terry


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## petertha

Terry, now that I see your complete exhaust fit-up, I am seriously thinking about re-engineering the intake/exhaust system on my radial. The head design inlets are tapped M10 for a coupler nut which clamps the 8mm tube to an inner counterbored face via a raised flare on tube end. There are other bits & pieces I wont go into detail, but collectively seems a bit fiddly & iffy to me seal wise & strength wise compared to a permanently attached header boss stub glued & set screwed into the head like you appear to be doing. And then the pipe gets attached via bolted flanges + gasket. Coincidentally this is the second instance I have seen a similar technique, so perhaps divine intervention.

Anyway I wanted to draw your attention to link below starting ~ post #245 where Mike discusses his choice of adhesive (JB weld vs Loctite type retainer) on similar header bosses & also his torch & wrench bench test. I know you have used HT retainer on valve cages etc. with good results, just wanted to mention for reference. In my case I don't have as much insert surface area working for me. And from what I could determine from JB 'specs', the high temp capability did look pretty decent all things being equal. Did you ever do elevated temp bench tests yourself?

 Mikes W165 Grand Prix engine   http://www.modelenginemaker.com/index.php/topic,5142.240.html


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## mayhugh1

Peter,
Thanks for the great link. I just don't seem to get over to the other forum as often as I should. 

I've never done any direct comparative tests between the temperature performances of JB Weld and high temp Loctite, but I did do some testing on JB Weld during my 18 cylinder radial build:
https://www.homemodelenginemachinist.com/threads/another-radial-this-time-18-cylinders.21601/page-12

See post #237. The JB Weld seemed to work to 500F, and from other testing I've done, I'm sure the Loctite would have given up before that. The prop wash over the heads of your radial will keep the head and exhaust temperatures well below the critical temperatures of either of these, and so either will probably work well for you.
Terry


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## petertha

Thanks for reminding me exactly where you discussed all that adhesive stuff. Excellent resource. 

Another question. It seems to me you used a similar Ridged style tube bender in the past for smaller diameter pipe. I get the impression they come nominally sized like 1/4, 3/8, 1/2 etc. You don't replace the forming head & rollers, you buy the tool for the tubing size, correct? What was the wall thickness of your SS pipes & did you have to do any pre/interim heating or core filling on those particular bends? They tuned out beautiful btw.


----------



## mayhugh1

Peter,
They do come in standard sizes for tubing, and the rollers aren't replaceable. I fixed the Amazon link I originally posted and so you should be able to search around for the others. I have a couple of these benders that I've used to do all my tubing bends since I like using stainless. No heat or core filling is required. The three rollers do about as good of a job as one could hope for without going to a mandrel bender. The wall thickness on the half inch tubing I used is .050". - Terry


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## mayhugh1

The dual spark CDI unit from cncengines.com arrived promptly after it was ordered. At 1.75" x 2.75" x 1" this new version of their ignition comes potted inside its own enclosure but is larger than the PC board units I've purchased in the past. The second coil in this particular model may account for some of the extra size. Testing showed the outputs fire on the rising edge of the input pulse (i.e. magnet moving away from the Hall sensor) which is how the previous generation units functioned.

My plan is to place the ignition behind a control panel that I'm adding to the stand near the front of the engine. In order to accommodate the starter, a sealed 12V lead-acid battery will be used for power. Since the CDI requires something less than 6V, it will receive its power through a step-down converter installed inside the control panel's housing. A second adjustable converter will be used to regulate the flow of a recirculating fuel pump that will supply fuel to the carburetor bowl. I've used these inexpensive converters in the past with no issues so far:

https://www.amazon.com/gp/product/B07DYPMPJG/?tag=skimlinks_replacement-20

A pair of holes were drilled through the side of the enclosure above each converter board in order to access its adjustment pot and for a light pipe to make its onboard led visible from outside.

The housing will also contain a 30 amp starter relay as well as a version of the Hall indicator circuit board that I've used on all my other CDI-fired engines. This indicator uses an led to display the state of the Hall sensor without need for powering up the CDI and dealing with its high voltage. This has been very convenient for engine timing and troubleshooting in the past.

The housing for the control panel will eventually contain a mixture of small signal, high voltage, and high power circuitry all operating in close proximity. Both converters as well as the CDI contain high frequency oscillators that, along with the starter relay, will generate plenty of electrical noise. I spent time arranging models inside a virtual housing in order to come up with a placement that will hopefully minimize interferences among them.

The control panel was recessed into the rear of its housing. This will bring a number of otherwise protruding switches and indicator lights within the protective envelope of the enclosure. The real reason for doing this, though, was to make an otherwise boring box into something a little more interesting to work on. The enclosure was milled from a chunk of ebay Delrin that wound up mostly as chips. Fortunately, the block was thick enough to yield a slice for its cover.

The panel connectors for the Hall cable, starter motor, and fuel pump will be JB Welded into the rear side of the enclosure. Since Delrin's slick surface isn't conducive to good adhesion, the joints were designed with internal irregularities which will grip and stabilize the essentially potted connectors. A standard Futaba J servo connector will be used for the Hall sensor cable, but the RC aisles of a local hobby shop were shopped for the other two connectors.

In order to help test the starter system, I made a temporary clear plastic plate to support the outer ends of its driven shafts inside the cam box. This will allow me to see the chain drives in operation since they will later be hidden behind the cam box cover.

The plug wires will be brought out through the enclosure's cover in order to keep them as far away from the Hall sensor wiring as practicable. I had a bit of fun with the cover design which resulted in a lot of extra machining to make it look like a heat radiator. Even though the enclosure may seem to be larger than necessary, it looks like it will be filled almost completely with electronics. - Terry


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## tornitore45

> This indicator uses an led to display the state of the Hall sensor without need for powering up the CDI and dealing with its high voltage. This has been very convenient for engine timing and troubleshooting in the past.



Good idea, I think will steal it for the Hoglet.
My guess is that you need an extra switch to power
the Hall-Sensor-Statuts- Indicator without powering up the HV board.
Or did you come up with some clever way to avoid it?


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## mayhugh1

Mauro,
Right now, as far as I can see, it requires a second switch. On my panel, the PWR switch will enable power to the control box including the indicator board. The IGN switch will turn the CDI on. 

I'm working on a schematic now. The new CDIs have their own indicator led built in, but it's powered along with the CDI and closely attached to its potted enclosure. I'm currently making  input measurements on the CDI to determine what its input actually looks like in order to ensure there isn't going to be any interaction between that one and mine. -Terry


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## tornitore45

I was thinking of placing decoupling diodes in the VCC to the sensor. Both sources can feed the Sensor but can not back feed the other box. 
One never know what kind of equivalent circuit is presented by a powered down Black Box.

As of now I have remoted the original LED but the HV still needs to be active during the adjustment phase.


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## mayhugh1

Mauro,
I was thinking the same thing. I've determined there's a dropping diode between the Vcc line and the rest of the CDI which is what was done on the older units. - Terry


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## ecdez

First time seeing this thread and I just scrolled through 9 pages of awsomeness.  Excellent work!


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## mayhugh1

Embedding the three panel connectors and their associated hookup wires into the side of the enclosure took a few days since each one required a couple steps separated by some JB Weld time. With the connectors finally located, I was able to make up the cable to the starter motor as well as shorten the sensor cables made earlier so they could be routed safely away from the flywheel.

After coming up with a wiring diagram, it was 'only' a matter of installing and soldering the various electrical components together. Along the way, I realized my enclosure had a poor form factor for how I was trying to use it. So much wiring had to be shoehorned into the spaces among the already mounted components that it quickly turned into a rat's nest.

I had planned to use one of the spare sensor indicator boards left over from one of my earlier engines. However, I discovered yet another version was needed with some additional terminals in order to avoid burying connections that might be useful later for troubleshooting. I probably should invest the effort required to learn proper PCB layout software, but with only one trivial board every couple years, I'll likely continue (mis)using SolidWorks. I tried my best to make sure that it will be possible, even if difficult, to replace failed parts. The kludge I created inside the control box isn't pretty, but it works as intended.

Unfortunately, the starter tests uncovered an unrelated problem. When finished, I could feel some roughness in the one-way bearing being used as a clutch. Under a microscope I could see some very light sprag marks beginning to show up on the countershaft. This was a nasty surprise since the starter had only a few minutes of operation on it. I had hoped the 1144 alloy used for the bearing's inner shaft would stand up to the sprags, but I was wrong and ended up machining a new shaft from O-1 drill rod. After a soak at 1475F, it was quenched and tempered at 350F. I couldn't measure any distortion resulting from the heat treatment, and so my original concerns that steered me to 1144 now seem unfounded.

The last step before our house begins filling up with family for the holidays was to machine a crow foot hold-down for the distributor. After the holidays, I'll likely start working on a fuel tank and fuel pump housing that will also be attached to the stand at the rear of the engine. I'm hoping to come up with something a bit different from the typical cylindrical tank. With the frustrating control panel wiring out of the way, it'll be nice to start making chips again.

My best wishes to all for a safe and happy holiday. - Terry


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## stragenmitsuko

For a milled  pcb  you board looks *very* clean . 
Most of the time marks from the cutter ruin the looks of milled pcb  . 
That doens't affect functionality tough , its merely cosmetic . 
But yours looks as good as an etched pcb . 
Nice work ! 

Just wondering , why did you put the parts on the "wrong" side of the pcb ? 
Usually  for a single sided board  that is , the parts are on one side , and the copper traces on the other . 
That's why these pcb ar called thru hole mounted . 
As opposed to smt wich are  surface monted . 

Pat


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## tornitore45

Mounting components on the circuit side has one advantage:
You can "read" the schematic just looking at the board.
Since usually a "good engineer" has the schematic memorized it help to find the right node to probe when debugging.


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## JRD56

Hello, New to the forum and I just started looking at your thread.  I love the mix of mechanical and electrical engineering.  Could you explain how the Hall Sensor triggers the CDI.  What is the purpose of the 2N2222?


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## dsage

Hi Terry:
I assume you're using one of Roy's original CDI modules?
Don't they issue a spark on the Positive going edge of the trigger?  i.e. the Hall sensor output goes low (with the magnet) and the spark is issued when the magnet disappears and the hall sensor output returns high?
 I'm not saying anything is wrong with your arrangement as long as you realize that your spark will occur when your led goes off, not when the led turns on.
It's been a while since I used the modules but I thought they were made to duplicate the action of a Kettering ignition (as above).
Did he change something?
Nice job as usual.


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## mayhugh1

Thanks all for your comments and questions.

Pat,
I would normally put the parts on the correct side, but these simple sensor boards usually end up embedded in tight quarters and putting the solder side up make it easier to remove/replace a failed component without pulling the whole board. There's also a lot to what Mauro said. 

The copper thickness on the boards I'm using is .005" and I'm removing it with a .063" 4 flute cutter running at 5000 rpm, 5 ipm, and a .010" depth of cut. I, too, am surprised the result is so clean.

JRD56,
The purpose of the little circuit board is to provide an indication of the state of the sensor without powering up the CDI. It's convenient for timing and troubleshooting that doesn't require plug firing since you don't have to remember to provide spark gaps and engine grounds for the high voltage outputs which could otherwise blow a Hall sensor or create latent internal damage to the high voltage coils. These precautions are absolutely necessary, easy to forget when your mind is focused elsewhere, and must be in place every time power is applied to the CDI. Roy provides a similar interface and indicator led for the sensor inside his unit, but the unit must be powered to use it. My PWR switch energizes my indicator, while the IGN energizes Roy's indicator and CDI. When the engine is normally running, both are energized and running in parallel. The 2N2222 is just the switch turning my indicator's led on and off.


Dave,
I'm using one of Roy's dual CDI's and it works exactly as you say. When timing the engine I use the led coming on as a warning that the magnet is 'dwelling' in the vicinity and that the spark is soon to follow. It's just a personal preference and a carry-over from the old Kettering systems where there is a dwell period and then a point opening that fires the plug. - Terry


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## dsage

Thanks Terry:
That's what I figured and it's the way I like to arrange it as well.
I also like your approach to the circuit board. I'll have to remember that one.
Thanks


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## JRD56

Thanks for explanation Terry.   Back in my younger days I was a drag racer and used MSD ignition systems.  With an MSD you always need a "load" if it was powered up and the engine turned over.  Otherwise you'd fry it.  I saw quite a few guys pull the coil wire and use the starter to turn over the engine to set the valves, etc thinking it was the right thing to do.  Unfortunately they fried their MSD.  Your approach definitely helps to avoid a similar failure.


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## mayhugh1

My goal for the fuel tank was to come up with something other than a classic cylindrical tank. A bike tank would have been novel, but it didn't seem appropriate connected to an engine installed on a test stand. YouTube videos show bike shops hanging all sorts of containers above the engines they test - some not so appropriate. While searching the web for ideas, an HDPE blow-molded tank caught my eye. After thinking about it over the holidays, I decided to create something similar in metal.

An electric fuel pump will allow me to place the tank low on the stand so it's kept subordinate to the engine. I've used fuel pumps on all the multi-cylinder engines that I've built and have been very happy with the consistent fuel delivery they provide. Although I've prominently displayed them in the past as accessories, I didn't want this one visible along side an old school motorcycle engine.

The three-piece tank design that I came up with is shown in the SolidWorks assembly photos. Although I'm trying to make the top portion of the assembly look like the fuel tank, it's actually an enclosure that I'm using to hide the pump. The tank itself is the bottom half of the assembly and separated from the pump's enclosure by an o-ring'd spacer. For safety, it's important to completely isolate the tank from the pump in order to prevent gasoline fumes from accumulating inside the enclosure around the brush motor. The tank's capacity is about 2-1/2 ounces which should provide some 10 minutes of run time. Realistically, though, the engine most likely won't be able to continuously run that long without overheating.

The fuel pump that I'm using is the same commercial product that I've used in the past. RC enthusiasts have been fueling their planes with this particular pump for many years and, remarkably, it's been available from my local hobby shop for over a decade. Although the manufacturer doesn't recommend its use with gasoline, I've been pumping gas with these pumps for years with no problems so far. The pump quickly self primes and, in recommended use, is typically located above the fuel source. I like using them in this same way because their rigid shaft seal stays dry except when the pump is running, and the risk of leaks is reduced.

The fuel pump consists of a pump coupled to a small dc motor through an Oldham coupler. The motor is designed to be operated from 6 or 12 volts. The variable voltage source inside the control panel's enclosure will be used to fine tune the flow rate of the recirculating loop once it's finally running.

I typically remove the pump and motor from their factory plastic enclosure and repackage them in a more appropriate machined metal enclosure. The machining of the recessed supports that hold the two in alignment is rather involved and essentially duplicates what was molded into the original enclosure. Several years ago, I invested effort in developing the CAD/CAM to reproduce it, and the Knucklehead's pump will be my sixth re-use of it. To protect my investment, I stashed away a couple extra pumps.

Although it complicated the design, I routed the pump's pickup tube wholly within the assembly so that all external fuel lines could emanate from the upper section and help maintain the illusion that the upper section is the tank. This required modifying the pump's input feed tube. I also plan to bring the electrical connections for the motor out to a panel connector mounted on the bottom of the assembly. This will require a pair of spring-loaded electrical contacts mounted between the tank and the pump enclosure but outside the o-ring seal. - Terry


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## gbritnell

Terry, Happy New Year to you and your family. I really enjoy your designs for the ancillary parts and pieces. It's almost anticlimactic when the engine runs and we don't get to follow along any more, just waiting for the next project.
gbritnell


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## mayhugh1

Thanks, George. I greatly appreciate your comments. May the new year bring you and yours new knowledge, satisfaction, and riches. - Terry


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## mayhugh1

Construction of the fuel tank assembly began with the topside surface of the pump enclosure. Even with CNC, the complex filleting that makes up much of its design also makes it a finicky part to machine. Stacking fillet upon fillet can become infectious, but wrinkly surfaces it can sometimes produce are difficult to detect except on the finally machined part.

My goal, which I only occasionally achieve with 3D parts, is to put the necessary upfront effort into making the mill do all the work to produce parts that require no additional cleanup beyond bead-blasting. The 80 grit media that I use is capable of removing machining marks up to two or three tenths deep in aluminum without altering delicate features on the part's surface. Scotch-Brite can help with another tenth or two, but I typically use 800 grit paper for defects on the order of a thousandth. Anything over that is first roughed out using fine rifling files.

My CAM software begins by sewing all the fillets, contours, and flats together into a single surface for use by certain of its machining operations. In most cases, though, it's more practical to work on individual or small groups of individual features rather than continuously machine and re-machine the entire part. This does create the potential for leaving appearance-spoiling artifacts behind in the boundaries between operations, though.

For a nicely blended result, the CAM software needs to know the precise lengths and diameters of all the cutting tools. Relative errors on the order of tenths among them will be visible in the boundaries between operations. I try to design my parts to require a minimum number of cutting tools and, if at all possible, a single ball cutter for handling all the finishing operations. The detail I designed into the top surface of the pump enclosure, however, required three different size ball cutters in order to efficiently remove the material left behind by the roughing tool. This greatly reduced any chances of me meeting my goal on this part.

In order to complete the machining in a reasonable amount of time, the CAM software also needs to be told how much deviation from what it believes to be perfection is allowed. Errors can result from a slightly different interpretations of this deviation among different contours with different shapes and slopes even when they're adjacent to one another. Spreading lengthy operations over multiple machining sessions that require re-referencing the workpiece also adds errors.

Machining of the pump enclosure began by drilling a hole through the workpiece for the filler cap. Its exact location was immediately indicated and recorded for a later sanity check. This hole will also be used as a reference when the part is flipped over for its bottom side machining. A two hour roughing pass with a 3/8" 4-flute cutter was immediately followed by three hours of finishing passes using 3/8", 1/4", and 1/8" diameter ball cutters. The lengths and diameters of these cutters were carefully measured, including the effects of runout, before they were supplied to the CAM software. The location of the reference hole was remeasured after the five hour machining marathon and found to have shifted only .0003" in the y direction and nothing in the x-direction - not bad for stepper motors.

The photo shows a well-blended final result except for some very disappointing horizontal gouges on the front surface that are several thousandths deep. These are often created by long sharp-edged roughing tools when machine and/or tool deflection and chatter combine with an unfortunate tool entry. The problem can easily and should have been avoided by leaving excess stock during the roughing pass for the finishing tool to remove. I always set up operations exactly that way, but for some inexplicable reason I did not this time. Bead-blasting removed all the other finishing defects, but filing was required to clean up the gouges.

The exterior of the actual fuel tank was machined next. Its surface is considerably simpler and was designed to be finished with a single ball cutter. The same long roughing cutter was used, but this time .010" excess stock was left behind for finishing that resulted in no gouging. The roughing tool was also used to finish the part's flat surfaces while the ball cutter finished the vertical surfaces including a huge fillet between the two. Tool measurement errors are apparent in the boundary between the two operations under the part's mounting flange. Since the error is on the underside of the part, it was left as is.

The internal surfaces of both parts were finally machined, and the pump and motor were trial-fitted. During the design of the tank assembly, I was looking forward to trying my hand at home anodizing the parts. With them finally in my hands, though, I felt they were too complex for me to properly polish for an anodized finish that I'd be happy with. I decided instead to paint the outer surfaces with Gun-Kote. Since this paint requires an oven cure, the electrical contacts must be added afterward.

A few changes for safety were added to the design shown in my previous post. The first was an array of vent holes drilled into the rear of the pump enclosure near the motor's brushes. The spacer plate will also be notched to create a weep hole in the pump enclosure in order to drain fuel in the event of a pump leak. The final steps will be to machine a filler cap and separator plate with pickup tube sub-assembly, install the electrical components, and then finally test the whole assembly. - Terry


----------



## petertha

That turned out really well.
- I've never played with those bake on sprays like Gun-Kote. Do you have a sense if parts can be touched up or entirely re-sprayed with the same system or is it kind of a 1-shot deal?
- those tabs or finger holding the motor is neat. So does that entirely support the motor kind of like a loose press in fit, or maybe will be sleeved with rubber or something?


----------



## mayhugh1

petertha said:


> That turned out really well.
> - I've never played with those bake on sprays like Gun-Kote. Do you have a sense if parts can be touched up or entirely re-sprayed with the same system or is it kind of a 1-shot deal?
> - those tabs or finger holding the motor is neat. So does that entirely support the motor kind of like a loose press in fit, or maybe will be sleeved with rubber or something?



It can be touched up after it's cured and then re-baked. It's pretty durable. I made some motorcycle parts some dozen years ago and painted them with that paint, and it held up in the weather during the 80k cross country miles we put on that bike.

Those tabs were designed .010" oversize for the pump and motor that I had available when I designed them. I then file them for a snug fit as needed for the particular motor/pump combination that I end up with. I do typically use a rubber pad between the pump and the enclosure's cover plate which in this case will be the spacer plate. - Terry


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## kvom

I really do need to get a bead blasting setup.


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## mayhugh1

Construction of the fuel tank assembly continued with the machining of the spacer plate. It was milled from a piece of 3/32" hard aluminum sheet that was temporarily glued down to a piece of sacrificial MDF. The top surface of this plate will close up the bottom of the pump enclosure, and its bottom face will o-ring seal the top of the fuel tank. A fabricated brass elbow, bolted to the top of the plate, connects the pickup tube to the fuel pump through a short length of Tygon tubing. An o-ring surrounding the threaded filler hole on the bottom of the pump enclosure seals the spacer plate's through-hole.

The elbow's tiny gasket was cut from .020" teflon sheet using a 60 degree drag knife on my Tormach. Although I'd normally drill the clearance holes for the 1-72 mounting screws in a separate operation, I was pleasantly surprised to find the drag knife was able to cut them out perfectly. This gasket not only maintains the integrity of the seal between the tank and the pump enclosure, but it also eliminates a wet aluminum/brass interface that might otherwise have become a site for galvanic corrosion.

A pair of spring-loaded contacts mounted between the halves of the assembly will carry current to the pump motor from a connector mounted on the bottom rear of the tank. I used commercially available contact pins from Mouser Electronics (and others):

https://www.mouser.com/ProductDetai...30-002101?qs=sGAEpiMZZMvQ0fyxs12AwCm1WaLxvbzX

These spring-loaded contacts were designed for use on fixtures used to test circuit boards. This particular 3 amp contact contains a 2x2 array of gold-plated long-travel pins. After cutting it in half, the solder side of the second pair was used for the stationary half of the mating pair. Wires were soldered to each connector before epoxying them into the mating flanges. The contact through-hole in the spacer plate was used to ensure the contacts ended up properly centered over each other.

These tiny contacts are fragile though and vulnerable to damage if the tank halves are allowed to laterally slide over one another during assembly/disassembly. To prevent this, a pair of dowel pins were added to the pump enclosure's flange. A threaded o-ring'd filler cap machined from 12L14 and painted with Gun-Kote completed the fuel tank.

After final assembly, the tank was bolted down to the engine stand, filled with fuel, and temporarily connected to an elevated dummy carb bowl for testing. After initially powering up the motor to determine the polarity needed to spin the pump in the proper direction, a cable was made to connect it to the control panel. Once completed, the recirculating fuel loop was tested for several minutes and appeared to work as expected. The motor's voltage is adjustable from the control panel and will be fine-tuned after the carburetor is completed. That carburetor seems to be my last excuse for not returning to the pushrod covers. - Terry


----------



## mayhugh1

Gasoline begins boiling at about 100F, and so carburetor temperature is a concern in any air-cooled engine. The Knucklehead's carb is particularly vulnerable because it sits on the end of a long intake tube that will essentially be spit-roasted in the V between the cylinders. In order to reduce the heat conducted to the carburetor, the intake was fabricated from stainless steel which has very poor thermal conductivity (roughy 5% of that of copper). For good measure, an insulating spacer will also be added between the two.

The carburetor provided in the drawing package is fairly ambitious and has everything one would expect to see on a full-size design including a float/bowl assembly, high/low speed needles, a butterfly throttle, and a choke. Except for the throttle which is controlled by an imposing cable assembly, access to its adjustments seem pretty limited. Since a model engine typically spends most of its active time idling between occasional throttle blips, I made modifications to the design to improve access to the low speed adjustments without giving up high speed control nor altering the essence of the original carburetor.

Since it was designed to accommodate a float, the original fuel bowl is rather voluminous for the engine's scale, and its depth limits access to the high speed needle located on its bottom. Its diameter also shifts the air cleaner further away from the engine than I'd like. Since my fuel pump eliminates the need for a float, I reduced the volume of the bowl, made it square instead of round, and chamfered its front end for better access to the high speed needle.

I left out the throttle control cable which seemed to overwhelm the presentation of the engine. My throttle control will be a simple spring-loaded arm located on the butterfly shaft behind the air cleaner and finger accessible from the top of the engine. Throttle return will be accomplished with a hairpin spring located inside a rotating cup that also raises the arm above the valve box oil return lines. I moved the adjustable idle stop into the cup assembly since the original version pointed into the rear head. I also added a fixed high speed throttle stop to prevent over-travel. The idle mixture assembly was left essentially unchanged since its needle appears be accessible through the front pushrod assemblies. The high speed needle assembly at the bottom of the bowl was left unchanged for the time being, but its length will likely be shortened later.

The choke control arm was designed with two detent positions: full ON and full OFF. A spring-loaded ball will lock the choke in either position but will also supply the force needed to hold the choke in an intermediate setting. All controls will be accessible behind the air cleaner which itself will be just a polished cover with no rear plate or filter element.

The original carburetor was designed to be a multi-part soldered assembly. Because of engine vibration, I was concerned about the 6 oz lump of brass that SolidWorks predicted would be hanging off the unsupported end of the 5" long intake tube. After a lot of back and forth, I decided to change the material from brass to aluminum for a 3X weight saving and to assemble the parts using JB Weld instead of solder.

Even with the material change I decided to maintain the same close-fitting joints I had planned for the soldered assembly. However, I couldn't find any reliable data on JB Weld's minimum usable glue line thickness. I ran some experiments and determined that a .002" glue line was practical and would provide more than adequate strength between two bead-blasted aluminum surfaces. The 1/16" test plates in my peel tests bent before the epoxy failed. For good measure, though, I'll also add pins to the joints where practical. - Terry


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## mayhugh1

I've been looking for an excuse to build up a complex bonded aluminum assembly for some time. I'd have preferred using white metal for a number of built-up parts in the past, but I always settled on using brass so their components could be soft-soldered. My concern about the weight of the Knucklehead's carburetor, whether valid or not, gave me an excuse to try my hand at building up a four-piece assembly. For adhesive, JB Weld met all my requirements with its high strength and service temperature and especially its compatibility with gasoline.

My mini project began with the machining of the carb's main body. After turning a starting work-piece that resembled a thread spool, it was moved to the mill so the front and rear mounting flanges could be machined. Except for some matched-drilled holes that will be added later, a locating hole for the high-speed jet/pick-up tube and a flat mounting surface for the top of the bowl finished up the first piece.

Although the bowl top is square, it has a number of circular features that made it more sensible to start with a piece of round stock and perform the bulk of its machining on the lathe. The remaining features of this second part including its square perimeter and a recess for the bowl gasket were completed on the mill.

Before bonding the two parts together, arrays of .010" deep grooves were milled into their mating surfaces in order to hold additional adhesive. These grooves were designed to wind up on top of one another and create a series of .020" thick glue lines after the parts were assembled. A .022" alignment hole was drilled through both parts so a temporary seamstress' pin in conjunction with the locating hole for the main jet held the two parts in alignment while being epoxied. The tiny alignment holes were drilled through the center of what will eventually become the bore for the throttle shaft. The parts were then bead-blasted and cleaned in warm soapy water before a thin layer of JB Weld was applied to each mating surface. Because the shop temperature has been in the low sixties lately, the epoxy was warmed with a heat gun before being mixed in order to reduce its viscosity.

The bottom half of the throttle assembly, a circular boss, was turned to its finished diameter, and a .022" locating hole was drilled through its center. It's bottom face was then contoured for a +.002" fit to the carb body. The face of this contour contained an array of .001" high scallops intentionally left behind during machining to provide some extra byte for the adhesive. The corresponding area on the carb body was also scratched up with a Dremel engraver. Following the surface prep described earlier, the bottom half of the throttle boss was JB Welded to the top of the carb body. After an overnight cure, its internal features were machined in place on the carb body including the recess for the hairpin return spring, the idle stop boss, and the bore for the butterfly shaft.

The last part in the bonded assembly was the boss for the idle mixture screw. This tiny and complex part has two mounting surfaces but with little surface area. Each was machine-contoured to produce a +.002" glue line. In order to augment the strength of the epoxy bond, its pickup tube will later be Loctite'd and extend through the top of the bowl and partially into the boss.

The final assembly was once more bead-blasted and thoroughly cleaned before receiving a two minute dip in Alodine:

https://www.amazon.com/dp/B0049CDP5W/?tag=skimlinks_replacement-20

Alodine is a chrome-based surface passivation treatment designed for use on aluminum alloys. It's commonly used on military hardware because of the salt spray resistance it provides. Old-school hot-rodders familiar with Holley carburetors will recognize the golden tan color that it leaves behind.

So, what did I learn from this little experiment? During the setup to machine the internals of the bonded throttle boss, I discovered it was offset from the center of the carb body by .009". I wasn't able to determine exactly what went wrong, but I suspect the error was related more to my alignment scheme rather than the use of epoxy. I decided to keep the throttle shaft centered in the boss during its machining and to later compensate for the error by offsetting the butterfly on its shaft. If I were doing it over, I'd complete the machining of the boss before bonding it to the body, but more importantly I'd use a full diameter temporary throttle shaft to hold the parts in alignment. After thinking about it, I realized my alignment scheme using the tiny needle was pretty dumb and that I had been too focused on a larger pin becoming inadvertently epoxied in place.

I learned that it was nearly impossible to maintain a consistent .002" glue line between two complex contoured parts regardless of their machining. Inherently, this would not be a problem with a soldered assembly. The viscosity of even warm epoxy is just too high, and .005" - .007" is a more reasonable expectation between a pair of non-planar parts. Although I didn't have to deal with joint strength, it's typically not a major spec in assemblies that are going to be soft-soldered. - Terry


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## kvom

I hadn't heard of "alodined" before.  Learn something new every time I come to this thread.


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## propclock

Fascinating build with exceptional sharing of the build . Thanks ! I also have never heard of Alodined.
For my 1.414 cents worth, My friend glues up his radiators from heater cores and makes custom top/bottom tanks.
He uses BONDERITE C-IC 33 AERO (FORMERLY ALUMIPREP 33)  for final clean up before the epoxy. 
I have seen it in action and it truly makes a perfectly clean bonding surface on aluminum. 
Thanks again!!


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## petertha

Very nice looking parts Terry. Its interesting that most epoxy specs talk about gap filling capabilities but rarely mention much about minimum gap distances. I have heard about dry joint or over clamping which is maybe another way of saying the film is very thin. But nothing very specific or quantified in terms of structural weakness. In hindsight if you knew you were going to be dealing with more precise components with gap distance within the what  typical retaining compounds specify as allowable, do you think that would be a better option over epoxy? Or are there other attributes to consider?


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## mayhugh1

Petertha,
If I understand your question, you're asking what would one do if some important dimension depended upon the previse thickness of the glue line. One option would be to build excess stock into the part and then finally machine it after bonding. I did that, in fact, with the lower half of the throttle boss. Its final height above the carb body was machined after the epoxy cured. An effective .002" glue line in a soldered assembly is inherently easy, but precise positioning of the parts are still an issue - probably more so than when epoxying them in place since you can continually measure and tweak their positioning before the adhesive sets up. - Terry


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## petertha

Sorry, clumsy wording on my part. If I had a stack-up of parts to make a similar assembly like your carb, where the components  fit decently well; flatness, minimal gap between them, no requirement for adhesive fillet forming  etc. Do you think Loctite retainer type adhesive would still be a viable way to join components, or does epoxy still offer other advantages in your opinion? 

For example I made a simple holding fixture turned in the lathe & attached an aluminum part with retaining compound using light tail stock clamping pressure until cured. The light cut machining on the part went fine, nothing came flying off. But what surprising was removing the part without damaging it was more effort than I expected even with moderate torch heat. So I tucked that away in my brain for similar built up assemblies.  I've just never used retainer outside of typical bearings & threads.


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## kvom

If I understand the JBW technique, the grooves are filled flush to the surface with no overflow onto the adjoining surface.  Correct?


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## mayhugh1

Petertha,
I've tried using Loctite (bearing retainer) in that way in the past but never had any luck. I always suspected it was probably because Loctite has good sheer strength but poor peel strength. I'm not aware of any low viscosity metal-to-metal adhesives that I'd trust, but really my only other experiences are with super glues. - Terry


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## petertha

Perfect, that's what I was wondering.


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## mayhugh1

Kvom,
I smeared a thin coat over the entire mating surfaces, applied pressure to  the assembled pair, and cleaned up the squeeze-out with Q-tips. -Terry


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## rodue

kvom said:


> I hadn't heard of "alodined" before.  Learn something new every time I come to this thread.


Being a retired airline employee Alodined  is a acid coating used on aluminum before painting it is a treatment    for corrosion prevention


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## doc1955

rodue said:


> Being a retired airline employee Alodined  is a acid coating used on aluminum before painting it is a treatment    for corrosion prevention



_You were an airline employee I worked for airline cargo systems company for 43 years before retiring.
I have been on the sidelines and must say you do some beautiful work and designing stuff out is really nice!!_


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## rodue

I am having a problem deciphering the push rod housing from the print, a assembly drawing in detail  I can't find. I hate to start changing from the drawing.


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## mayhugh1

rodue said:


> I am having a problem deciphering the push rod housing from the print, a assembly drawing in detail  I can't find. I hate to start changing from the drawing.


My problem as well. Its design is important in order to not introduce serious oil leaks, and I don't see how the current design does that. I've been putting off working on it hoping my subconscious would  come up with a solution. So far, it hasn't, and after the carburetor I won't have any excuse but to return to it. - Terry


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## mayhugh1

Work continued on the carburetor with the machining of the bowl. Because of its thin walls, a boss was designed into the bowl's interior to support the inlet and outlet hose barbs. The barbs were turned from 303 stainless, threaded, and Loctite'd in place with permanent thread locker. They were installed after finishing the bowl's exterior machining but before starting its interior. The interior machining was designed to uncover the ends of the barbs and smoothly blend them into the walls of the bowl. The finished bowl was bead-blasted and Alodine'd similarly to the body that was finished earlier. Both were then lightly polished with a white Scotchbrite pad to distress and lighten their final colors for a better match to the cadmium dichromate plating on an old school carb.

My original plan was to seal both the top of the bowl and its bottom main jet exit with gaskets. I wasn't totally happy about both gaskets having to seal under the same clamping force, and so I changed the bottom seal to an o-ring. This o-ring will be compressed by a hard stop on the main jet just before the upper gasket begin to compress. The bowl gasket was cut from .015" teflon sheet using a drag knife on my Tormach. A large-headed screw was used to temporarily assemble the bowl to the carb top for leak-testing.

The components of the throttle assembly were machined next. Delrin, with its excellent gasoline resistance, was used for the butterfly disk to avoid metal-to-metal contact inside the carb body. The shaft was machined from polished drill rod. The tiny features inside the throttle-arm required a good bit of time with a 1/16" end mill, but an overly ambitious feed rate broke my only 1/16" ball cutter, and the exterior had to be finished with a file and abrasive paper.

Some experimenting with different wire sizes was required to get just the right hairpin spring for the throttle return. Standard spring wire suppliers tend to sell wire only in large expensive rolls, and so I searched local retail stores looking for some consumer products I could re-purpose. In addition to guitar strings from a local music store, I found several diameters of stainless steel spring wire being sold for use as fishing leader in a sporting goods outlet. The final spring was formed with 3-1/2 turns of .016" spring wire wound around a .111" drill bit. After cold forming the spring and several spares, they were annealed for a couple hours at 400F. A bit of grease on the inside of the cup assembly will help avoid chewing up its soft surfaces.

Because of hands and eyes that don't work so well anymore, I expected some difficulty in assembling the throttle with its internal spring. But, I wasn't prepared for the three full days it took me to come up with a spring and an assembly procedure that I could perform. In the process, several of my extra springs were flung somewhere inside the shop and never seen again. In the end, I drilled a .022" hole through the top half of the assembly for a straight pin to temporarily hold the pre-tensioned spring in place during assembly. To be honest, I didn't get that hole in the right place the first (nor the second) time I drilled it.

In the end, by offsetting the butterfly on its shaft in the opposite direction, I was able to compensate for the earlier issue that had caused the throttle shaft to wind up offset in the carb body. The size of the error was actually .0045" and not the .009" that I previously misstated. I eventually selected .007" for the clearance gap around it. The final throttle action is smooth, and the spring reliably returns the throttle to the idle stop screw with a good feel. And, I can even disassemble and reassemble it. - Terry


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## tornitore45

Terry, if you need spring wire I have several lifetime supplies of the following sizes.

SS      0.016    0.035
Music Wire     0.011    0.013    0.014    0.018     0.020    0.022      0.024     0.046


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## mayhugh1

Mauro,
Wow! Thanks, I'll keep that in mind.
Terry


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## Scott_M

Hi Terry

Awesome as always !!
Don't forget about Brownells,  Gunsmiths make a lot of springs. I have several of their assortments. Here is one of 100 12" pcs of assorted sizes from .02" to .062" it is music wire and not SS but they work great.

https://www.brownells.com/gunsmith-...-kits/no-150-small-spring-wire-prod26217.aspx

And thanks again for such detailed posts, they really are a joy to read.

Scott


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## mayhugh1

Scott,
Looks good. I did forget about them. Thanks!
Terry


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## mayhugh1

I received an email asking for more detail about how the throttle spring was installed. I've included a photo showing the top half of the throttle just before it was (re)assembled to the carb body. The moly grease makes it hard to see, but the spring is wrapped around a stub shaft temporarily inserted through the top half of the throttle. A straight pin is holding one end of the spring under tension. During assembly, the top half of the throttle is carefully centered over the bottom half before being pushed down over it. As this is being done, the spring slides off the stub and onto the throttle shaft, and the stub is pushed out through the top. A slight chamfer on the top of the throttle shaft improves the chances of this happening on the first try. With the two halves together, the pin is pulled, and the spring is released onto a stop in the bottom half. After tightening a grub screw in the top half, the butterfly keeps everything together. It's really not as hard as it sounds.

There's still a handful of small parts needed to finish up the carburetor, and for the most part they make up its various adjustments. I thought it best to have the air cleaner in hand before going any further with them since it could affect their accessibility, and some extensions might be required.

My experience with air cleaners on model engines has been that they seem to create more problems than they solve. My engines aren't run for very long and certainly not under 'severe service' conditions. High revving RC aero engines seem to get along fine without them. The foam elements that I tried years ago on my Howell V-4 changed the carb's air flow characteristics enough to affect its tuning. This would become a real annoyance if the air cleaner had to be removed to access the carburetor's adjustments. In any event, the air cleaner on this engine won't have a filter per se - just a cosmetic polished aluminum cover. Eliminating the filter element and its backplate will also allow the cover to be moved inboard.

Harley's stock air cleaner for the full-size Knucklehead was a simple circular dome. I like its clean looks and was looking forward to turning a scaled-down version. My CAD model, though, showed its diameter would have to be a little too small to avoid blocking access to the main jet on the bottom of the bowl. To get around this, I stretched its ends into a more interesting oblong shape. Actually, similar air cleaners were available later on Harley Panheads.

The cover was machined from a block of aluminum in two different setups, and its exterior was polished. The photos show some of the intermediate steps. A single cover's machining time was close to five hours due to my unreasonable obsession with its interior. The interior was shelled out to create a .050" thick wall as well as a pair of integral standoffs for bolting the cover to the face of the carburetor. With the air cleaner in place on the engine, though, access to the carburetor's adjustments don't seem to have gotten any worse. - Terry


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## mayhugh1

The photos below show what happened when I was having a couple of those days where I should have stayed out of the shop. The machining of the air cleaner cover in the previous post didn't go as smoothly as it may have sounded.

When the exterior machining of the first workpiece (the one on the left) was completed, I noticed a minor gouge on its top surface caused by a quirk in my CAM software. I've learned to check for this particular problem before cutting metal because it shows up in the displayed tool paths, and I can usually move a few parameters around to eliminate it. It occurs so infrequently, though, that I sometimes I forget to check.

I decided to try to save the workpiece by modifying an unimportant part of the design and re-milling the flat portion of the front surface another .005" deeper to remove the gouge. Since I didn't notice the gouge until after I had removed the workpiece from the vise, I had to re-reference it. This shouldn't have been a problem since I knew the coordinates of its two already drilled holes. Using a spindle microscope, I centered the spindle over one of them, but forgot the minus sign on the hole's x-coordinate when I initialized the control program with the new location.

When I started the machine, it promptly cut a much bigger gouge in the part as the cutter moved across the top of the workpiece to where it thought the new operation was to begin. If I had been thinking clearly, I could still have recovered the part by re-machining a whole new top, and this would have saved the workpiece and the machining time already invested in its periphery. The workpiece had plenty of extra stock on its bottom that would have allowed this, but instead I tossed it into the scrap pile. At the time I didn't know that the scrap pile was the safest place for it.

On the right of the photo are the remains of the second workpiece. Its new exterior g-code completed as expected. However, for one of the interior operations, I told the software that the diameter of the finishing cutter was .124" instead of its actual .249". (For some reason, my brain still stumbles over the differences between those two particular numbers.) Anyway, I started the machine and left to do some yard work. When I returned, I found a big pile of chips and a tiny carcass laying in the chip pan as well as a pair of .012" deep gouges in the faces of my vise jaws. Fortunately, the jaws are removable, and I spent the next hour or so regrinding them so I could begin machining a third workpiece.

The third time was literally a charm, and the workpiece made it through all five ridiculous hours of machining. I bolted the finished cover to a piece of wood that I had band-sawed for a close fit around its periphery so I'd have something to hold onto while polishing it. Unfortunately, the only long-enough 2-56 screws that I had on hand were SHCS's. After prepping the surface with 1000 grit paper, I took the part over to my buffer and loaded up the sisal wheel with some red rouge for final polishing. I was nearly finished when the wheel probably caught the head of one of the screws and ripped the part from my hands. The cover was flung around the inside of the wheel's circular dust collector before being launched over my right shoulder.

I was frozen for a few seconds but then started laughing hysterically. I went looking for the part and found it in a waste basket half full of discarded paper towels. I couldn't believe my luck, and my brain started questioning whether the previous few minutes had actually occurred. Although the piece of wood was pretty badly scarred, there was only a single barely perceptible mark on the part itself. Although in a different position, which will now become the bottom of the cover, the mark is strangely similar to the gouge that I started with. - Terry


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## tornitore45

Very entertaining post, but could not resist laughing... at your expenses.
Do not feel bad it took me 4 trial to make the Hoghlet cam.
1) Perfect job, just mirror image
2) I was going so fast I kept going and wiped out the lobe, a nearly cylindrical cam is pretty useless.
3) The center lobe is supposed to be twice the width but I goofed up and made it the same width as the others.
4) You know the universal saying:  4 times is a charm.


----------



## dsage

I have to laugh. Because so may times at shows when I say I've made something using CNC I get attitude (usually silence) that implies it was cheating and that made it easy. In fact CNC is not just slapping a piece of metal in the vise and push "go". I usually spend much more time drawing the part, generating and checking Gcode than it would have taken to make the part manually. In fact to take advantage of the CNC process, holding / clamping the piece can be a lot more difficult than a manual operation where you might be able to stop and move clamps around. My point is there is a lot of thinking that goes on when doing CNC and things can go bad really fast. I've made the same mistakes as you point out multiple times. Just a quick setup to "fix" a problem thinking you have it set so the original code will take care of it. NOT. And yes I've also scrapped a few parts after they are perfectly machined getting them through the finishing touches. LOL
Nice work.


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## Glorfindel

dsage said:


> I have to laugh. Because so may times at shows when I say I've made something using CNC I get attitude (usually silence) that implies it was cheating and that made it easy. In fact CNC is not just slapping a piece of metal in the vise and push "go". I usually spend much more time drawing the part, generating and checking Gcode than it would have taken to make the part manually. In fact to take advantage of the CNC process, holding / clamping the piece can be a lot more difficult than a manual operation where you might be able to stop and move clamps around. My point is there is a lot of thinking that goes on when doing CNC and things can go bad really fast. I've made the same mistakes as you point out multiple times. Just a quick setup to "fix" a problem thinking you have it set so the original code will take care of it. NOT. And yes I've also scrapped a few parts after they are perfectly machined getting them through the finishing touches. LOL
> Nice work.


Those who say it's easier on cnc, just dont know what they are talking about.


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## mayhugh1

The carburetor's Venturi is a separately machined aluminum piece that is Loctite'd inside the carb body. There isn't much clearance between it and the fully open butterfly and so, to be safe, it was positioned using a depth stop turned from Delrin. I removed the Alodine from inside the carb body with a medium Scotchbrite pad because I was uncertain about its compatibility with the Loctite. After curing, the hole for the main jet was drilled through the bowl top and into the bottom of the Venturi.

While the carb body was still set up on the mill, the hole for the idle jet pickup tube was drilled and a short length of .040" i.d. stainless tubing pressed in place. This completed the carb body's machining.

The components of the choke assembly were machined next. Their machining and assembly were much simpler than those for the throttle, and I was able to scrounge up a suitable detent spring without having to wind one. Two shallow spherical holes were drilled in the underside of the arm using a ball end mill in order to provide positive stops at full-on and full-off choke. The choke will come in handy during cold starts since, with an air cleaner covering the carb's intake, finger priming won't be possible. If needed, the spring-loaded ball should be able to hold the arm in any intermediate position even under engine vibration.

The main jet machining provided an opportunity to use a new (to me) technique for lathe turning long skinny parts. It involves taking axial cuts that don't produce first order radial forces that create tool and part deflections and their resulting chatter and taper issues. I learned about this technique in a video that Youtube 'recommended' for me a few weeks ago:



I reshaped a worn-out CCMT carbide insert in an SCLCL toolholder that I axially aligned to the headstock in order to approximate the cutting action produced by the special tool used in the video.

For the main jet's first machining step, I needed to reduce a half inch diameter 303 stainless rod to 1/8" over a length of 0.8 inches. Using this tool I accomplished it in only two passes - something that's nearly impossible on my lightweight lathe with conventional turning. Chatter was easily squelched by increasing the axial feed rate. The surface finish was very acceptable, and the taper was only a tenth or so. I've included a photo of this tool making the first pass on the main jet's workpiece. The camera shot required a flash that created some misleading shadows, but the insert's cutting edge is truly perpendicular to the spindle axis.

During earlier testing, I found it best to grind away all traces of the insert's nose and leave only a sharp corner in order to guarantee there'd be no radial cutting for near zero taper. Back clearance was also required to prevent the insert from rubbing against the workpiece behind the cut. Since I typically can't take deep radial cuts on either of my lathes, I have lots of worn-out inserts with virgin side edges that can be used in this operation. This operation would seem to be an efficient way to machine valves. A similar video in the same series applies it to turning extremely thin wall tubes.

The remainder of the main jet machining was routine except for a dozen .032" holes that were drilled radially around its 1/8" barrel. Even though I used a sensitive drill feed, it was difficult to find a sweet spot in the feed rate to get around stainless' tendency to work harden. I destroyed a couple (HSS and carbide) drills before I was done. Stainless, even 303, was a poor choice for this particular part - 12L14 would have been much easier to work with. Those innocent looking holes seemed a lot bigger on my computer screen.

I could probably have axially machined the jet needle assemblies from a piece of round stock, but for the delicate tapered portions I wanted the toughness of a high carbon sewing needle. My wife's hobby is quilting/sewing, and with the time I spend with her in notions stores I'm always on the lookout for things I can use in my own hobby. I chucked a number 18 darning needle in the lathe and re-tapered its end using a green silicon carbide dressing stick. A .046" hole for the needle was drilled in the end of a 4-40 SHCS that I used for the threaded body. In truth, there was a bit more to it. I agonized over the taper angle and its relation to the pickup holes in the jet's body before finally deciding I really didn't know what I wanted.

The idle jet needle is much shorter and was machined similarly, but it used a .020" diameter straight pin in the end of a 3-48 SHCS. The tiny hole in the end of that screw wasn't a lot of fun either, but by this time I knew to not use stainless. Although most Loctite retainers could probably have been used to hold the needles in the screws, blue thread-locker was the only one for which I could find specific recommendations for use in liquid gasoline. - Terry


----------



## petertha

*...technique for lathe turning long skinny parts. It involves taking axial cuts that don't produce first order radial forces that create tool and part deflections and their resulting chatter and taper issues.*

I saw the same video & tucked away the technique. One thing he didn't touch on - is there some rule of thumb relationship between the minimum base stock diameter & the finished small diameter? In your case you used 0.5" stock. For example do you think 0.375" stock achieve the same results on that small diameter & 0.8" stick-out combination?


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## mayhugh1

Petertha,
I don't have enough experience with it yet to say for sure, but I wouldn't see why not.  As long as the forces are all axial, I wouln't see why the starting diameter would matter. - Terry


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## mu38&Bg#

The forces aren't all axial. This method simply takes advantage of the stiffness of large diameter stock. Virtually all the cutting force is taken up by the large stock, instead of the thin part. Attempting to make the same cut with the stock 12" from the collet would have the expected problems. Any taper in the small diameter part is still due to stock deflection from cutting forces. You'd have even better results using smaller nose radius, smaller feed, and a lot of top rake on the cutting edge.


----------



## mayhugh1

Before setting the carburetor aside, I needed to know that it was basically functional. For a sanity check, I filled the bowl with isopropyl alcohol and blew 15 psi air through the carb's body. While exercising the throttle and needle adjustments, I looked for wet spray patterns on a paper towel at the carb's output. The low-flowing part-throttle patterns were difficult to see, but with a finger across the carburetor's output I was able to discern the difference between wet and dry air. I mainly wanted to make sure there were no chip blockages, that the needles had some semblance of control, and that each could be completely shut off. I wasn't expecting these tests to tell me much about the sensitivities of the adjustments - that will have to wait until the engine is up and running.

For the most part, the adjustments behaved as expected except for that of the main jet whose needle was shutting off the fuel much too early. This would have been a problem because of the limited space below the bowl for its travel. Since the taper I used was probably a bit too lazy, I chucked the needle assembly in the lathe and re-worked it with a dressing stick.

The last step was to set the voltage for the fuel pump. After some experiments, I added a half-inch long .035" diameter restrictor in the line to the carburetor. This limited the pump's more than adequate capacity inside the recirculating fuel loop. The restrictor allowed me to regulate a constant fuel level in the bowl over a rather broad range of pump voltages. The final voltage was selected to keep the bowl 80% full while unattached to the engine.

I got tired of looking at the piece of blue tape I'd been using to hold the far ends of the exhaust pipes together, and so I finally machined a proper collar for them. I wasn't able to come up with consistent measurements for the design of its i.d., and so I made an array of four parts with dimensions that I incremented by .002". After machining them in cookie cutter fashion, I trial fitted each one and found that the two middle parts best fit the pipes. I needed only one, but finish-machined both. Because of their nearly oval cross section, a clamp milled from a piece of wood was used to safely hold them in a vise for their backside machining. When completed, a setscrew was added to their rears that will slightly spread the pipes and hold them tightly in the collar under engine vibration.

I'm finally out of excuses for not returning to the point where I should have started work on the dreaded pushrod cover assemblies several months ago. There isn't much else left to do but to now go back and face them. - Terry


----------



## Scott_M

Beautiful work as always Terry !  I really look forward to your updates.
And while I know you have been putting off the pushrod covers I am certain that you will execute them with the same finesse and grace as all of the other parts in all of your builds.
They don't stand a chance against your shop "skilz"  

And thanks again for all of your detailed posts, they are a joy to read !

Scott


----------



## mayhugh1

Thanks, Scott. I really appreciate your comments.
Terry


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## kvom

Another lesson in why I won't every build an IC engine.


----------



## cds4byu

Scott_M said:


> Hi Terry
> 
> Awesome as always !!
> Don't forget about Brownells,  Gunsmiths make a lot of springs. I have several of their assortments. Here is one of 100 12" pcs of assorted sizes from .02" to .062" it is music wire and not SS but they work great.
> 
> https://www.brownells.com/gunsmith-...-kits/no-150-small-spring-wire-prod26217.aspx
> 
> And thanks again for such detailed posts, they really are a joy to read.
> 
> Scott



Another possibility for music wire is to contact a local piano tuner.  They usually have coils of various gauges that they use to replace broken strings, and I've found them very willing to sell me short lengths at a reasonable price.

Carl


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## johnny1320

Just Beautiful Terry!


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## dsage

Hi Terry:
In post 208 partway down  you  have what appears to be a continuous square profile rubber seal (I believe it's the fuel bowl cap). Maybe I'm just looking at the recess for same but what did / will you use for that seal?
And if it's just going to be a standard round O-ring, how do you keep it in place on a rectangular land.
Thanks


----------



## mayhugh1

Dave,
I cut that gasket from teflon sheet on my Tormach using a drag knife. It's sandwiched between the top and bottom of the bowl. There's a recess milled in the bowl top that it sits in. The recess is about half the gasket's thickness deep. - Terry


----------



## dsage

mayhugh1 said:


> Dave,
> I cut that gasket from teflon sheet on my Tormach using a drag knife. It's sandwiched between the top and bottom of the bowl. There's a recess milled in the bowl top that it sits in. The recess is about half the gasket's thickness deep. - Terry




Nice job. Going to have to get one of those.
Thanks


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## kvom

It's not as fancy as a drag knife, but I've success in cutting teflon gaskets with the sharp point of a chamfer mill.


----------



## mayhugh1

The pushrod covers are prominent parts on the engine with important requirements in addition to looking good. They must be oil tight but allow access to the lash adjusters they will also enclose. While the engine is running they should be positively secured at both ends yet allow their pushrods to be inserted and removed without major engine disassembly.

After completing the pushrod guide blocks several months ago, my plan was to continue on with the covers, and I spent hours studying the three-piece design provided in the drawings. Although the covers looked good in the downloaded renderings, I couldn't see any provision for sealing or securing them to the rocker boxes. I was also confused by some dimensional inconsistencies that I thought might be subtle tricks that I didn't fully appreciate.

Somehow I'd managed to successfully complete the nightmarish compound angle machining needed to align the cover tubes in the bores of the crankcase, guide blocks, and rocker boxes. The thoughts of re-machining any of those parts to accommodate a redesign of the covers was a real stomach churner. In order to continue progress I went on with the rest of the engine with the intention of returning to the covers later with a fresh perspective.

'Later' arrived, and for that perspective I modeled the three tubes making up a complete cover so I could play with the dimensions and virtually assemble all their possibilities. The first CAD drawing shows the models of the three tubes as well as their cross sections. It didn't take long to realize that I'd been overthinking the drawings. The dimensional inconsistencies were simply errors, and the design expected the upper tubes to be either glued into the rocker boxes or inserted without any special means of retaining them.

If they were permanently bonded, problems would arise when trying to install or remove the pushrods. If they were temporarily bonded with a sealant, the bond would need to prevent the upper tubes from working their way out of the rocker boxes under the engine's vibration. The second CAD drawing shows cross-sectional views of the covers in two configurations: normal running and lash adjustment. With no adhesive, the sliding fit at each end of the upper tube is all that's holding it in place. In addition, the three tubes need to be capable of being assembled or broken down with a pushrod inside them so the whole assembly can be maneuvered free of the guide block and rocker box. For me, verifying this would require some actual parts.

My experience with sealants in model engines hasn't been positive, especially when used on parts that may have to come apart again. Automotive sealants don't seem to scale very well. They're thick and messy and provide debris for clogging up tiny passages. They interfere with precision fits, and they're especially difficult to use between cylindrical parts. My goal was to avoid using them by making modifications to (only) the original cover design.

The first modification was to add a rocker box seal to the upper tube. An o-ring was my preferred solution but would have required re-machining the rocker box. Instead, I added a wrap of compliant material around the top end of the upper tube for a positive seal inside the rocker box bore. The third CAD drawing shows the machining required on the end of the upper tube. A short piece of Kynar tubing is heat shrunk into the groove that's machined around the tube's outer diameter. The design is such that after the Kynar is installed, its o.d. tapers slightly positive going from top to bottom and provides a snug fit inside the rocker box. As a bonus, its compliance increases the assembly's tolerance to small alignment errors between the bores in the guide block and rocker box. Kynar is a flexible but tough high temperature material with excellent resistance to a broad range of chemicals including gasoline and oil:

https://buyheatshrink.com/heatshrinktubing/high-temperature/kynar-heat-shrink-tubing

I tested and eventually used this material several years ago to solve a different kind of issue related to the assembly of my 18 cylinder radial (post #184):

https://www.homemodelenginemachinist.com/threads/another-radial-this-time-18-cylinders.21601/page-10

I used some of the leftover material to verify the design of the rocker box seal. After partially machining a couple upper tube ends and installing the Kynar, they were gently inserted into a container of oil. Neither showed any sign of leaking even after two days.

The second modification involved altering the threaded portions of the upper and lower tubes in order to create a threaded engagement during normal engine running. This engagement provides a controlled length adjustment of the assembly as well as the axial force needed to keep the upper tube snugly inside the rocker box and the bottom tube inside the guide block. The last two CAD drawings show the modified tubes assembled in their two configurations as well as side-by-side comparisons of the modified and unmodified parts.

In order to validate the design, a trial set of parts for a single cover was machined and test-fitted in all four locations on the engine. I also went through the exercise of installing and removing a dummy pushrod with the rocker boxes and guide blocks in place. The remaining photos show the actual first article parts. The upper and lower tubes were machined from aluminum, and the center cover tube was machined from 303 stainless. Now just three more sets of parts will finally wrap up my pushrod cover saga. - Terry


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## Scott_M

A very elegant solution Terry, it would seem that the fresh perspective was worth the wait ! Beautiful

Question , is there provision to keep them "adjusted" to that length ? Is running vibration a concern, that they may screw together ( get shorter ) ?

Scott


----------



## mayhugh1

Scott,
     I hadn't thought about them coming unscrewed. There's a good bit of friction between the upper and lower threaded tubes after they're tightened. Not so much on the cover tube though. - Terry


----------



## Scott_M

I am sure that in the amount of time it will run as a model, it won't be an issue. I was just curious how they dealt with it originally, or didn't  .

They all leaked

Scott


----------



## mayhugh1

Scott,
The full-size engines used a spring to force the upper and lower tubes apart and cork gaskets at either end for seals. Due to the design of the model engine's lower tube, only an upper seal should be needed. Gravity should take care of keeping the oil from collecting in the guide block and leaking out. - Terry


----------



## ddmckee54

Gravity will take care of the droplets and bigger stuff.  I assume the crankcase is vented so that any oily smutz floating around in the case will not be pressurized and seeking a place to escape?  Pistons banging up and down make a dandy air pump.

Don


----------



## mayhugh1

ddmckee54 said:


> Gravity will take care of the droplets and bigger stuff.  I assume the crankcase is vented so that any oily smutz floating around in the case will not be pressurized and seeking a place to escape?  Pistons banging up and down make a dandy air pump.
> 
> Don


Good point ...


----------



## Lloyd-ss

A beautiful and sophisticated project on so many different levels. I am thoroughly impressed. 
I do have a question that I hope you will answer. Back in post #2 you are using the C544 for one-piece guides and seats, and you mention that you have been using the C544 for quite some time.  So my question is about the longevity of the C544 as a valve seat. I am assuming that it either holds up very well or that you can re-lap it on an as-needed maintenance basis. Is that correct? Do you think the C544 would hold up in a diesel model as a valve seat, or should I use something else.  I am planning a diesel build and am trying to read about proper material selection for parts that have special requirements.
Thank you very much for presenting such a wealth of information.
Lloyd


----------



## mayhugh1

Lloyd,
I've used phosphor bronze for the seats and/or valve cages on all the engines I've built except for one, and that was because I had mismarked some regular bearing bronze as being phosphor bronze. I've not seen problems with either, but then my engines don't see more than three or four hours of running time. I personally prefer phosphor bronze for seats because it has an elevated temperature rating where as plain bearing bronze does not. The yield strengths of both are similar although bearing bronze is a bit more machinable. I once considered using aluminum bronze since it seems to be popular with others, but I found it hard to turn and difficult to get a nice surface finish on the seats. I once spoke withe Dwight Giles, a builder with much more experience than I have, about seat materials and he told me he used to use aluminum bronze but found it was causing too much wear on the stainless material he was using for his valves and so he was looking something else. The truth is, if you're using 7075 for the heads, integral seats are probably more robust than either bronze. A great seat surface finish would also be easy to avhieve. I've not yet tried it myself because by the time I get to the seats I have a lot invested in the heads, and it's much easier to scrap a bad seat than a bad head. - Terry


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## Lloyd-ss

Terry,
I really appreciate the personal response, and do not want to hijack your thread, so I will only ask a tiny bit more, and then start a build thread so as not to impose on others. For the project I am starting (52cc diesel, horizontal, crosshead) I was planning to use 12L14 for the head (with water passages), 316 stainless for the valves, normalized 4130 DOM tube for the cylinder (with water jacket), purchased Tanaka 1.5 mm thick rings,  and possibly Nitronic 60 stainless for the piston (very good galling resistance and I have some of it on hand). Your endorsement of C544 for the valve guides checks off another box in the material list. I admit that I'd rather work with 7075 for the head, but it is a simple design so the 12L14 will still be easy to work. I am guessing that you will say that with a 12L14 head, either the  C544 or the 12L14 head material will be suitable.  Again, thank you so much for your response.  The freedom with which you and all the forum members share their knowledge is much appreciated.
Lloyd


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## mayhugh1

Despite a bathroom remodeling project that's been sapping a lot of my energy, I managed to machine the rest of the parts needed to complete the remaining three pushrod covers. The photos show the finished parts and the mandrels used to turn them. The one-off expanding mandrel was machined with care and indexed to a collet since it was used to turn some of the features whose concentricities are critical to the fits of the final assembles. The much less important threaded mandrel is just a headless 5/16"-24 bolt used to hold the tubes in the lathe during polishing. A second bolt was used to confirm the internal thread count in each bottom tube. With my modifications, 13 to 14 full threads are required. Care is needed while threading the bottom tubes to avoid breaking out through their o.d.'s. Part of my initial confusion with the original drawings was that it looked to me like breakout would occur if this part were threaded according to its drawing.

The slippery polished surfaces combine with the very limited access while assembling them in place to make it difficult to install the covers in the two intake positions. I was eventually able to partially install all four assemblies so I could check for carburetor interference issues, but some kind of helper tool such as a tiny strap wrench is going to be needed for final assembly.

Excluding the pushrods, there are several more machined parts needed to make up the roller lifter/lash adjuster assemblies. The lifter machining looks like it will be particularly tricky not only because of the tiny parts involved but because the shafts for the 5/32" diameter ball bearings used as rollers will each have to be uniquely canted to compensate for the pushrod angles.

Don's comment about crankcase ventilation was timely, and although I'd previously provided for pressure equalization between the crankcase and the gear case, I realized I'd forgotten all about the road draft vent I had planned for the gear case. Instead of routing more tubing over its already busy exterior, though, I decided to incorporate a vent into the dipstick which sits relatively high on the engine. I modified its previously machined handle with an array of holes that I radially drilled into an internal plenum that I also bored into its center. A new stick, more complicated than the first, was then machined for it. This one has an integral tubular screen at its upper end that will hopefully strip some of the oil from the effluent as it's pumped through a labyrinth on its way out of the engine. Since it was essentially free, I also drilled out the centers of the five 10-32 button head cap screws that join the gear case to the crankcase in order to provide some additional paths for pressure equalization between them. - Terry


----------



## mayhugh1

This post comes a few days after the one-year anniversary of the start of this build. I had hoped it would be completed by now so I could start work on the Offenhauser, but this engine has been more challenging than I had originally anticipated. At the rate I work, I probably have another six weeks in front of me; but with all the home repair/remodeling work I'm currently involved in during the day, it might take even longer. Fortunately, I enjoy the journeys much more than the destinations that these builds tend to provide.

Before starting work on the lifters, it would be wise to have some semblance of a camshaft in my hands so I can check the operations of their rollers. Although the lifters in the model are similar to those in the full-size engine, their orientations are not. The lifters in the full-size engine are perpendicular to the axis of the camshaft, and the compound angled pushrods are accommodated using hemispherical cups on the tops of the lifters and spherical ends on the pushrods.

The model engine's lifters, on the other hand, are collinear with the pushrods. This departure from the full-size engine greatly complicated the machining of the guide blocks and now requires canting the rollers on the ends of the lifters so they can ride flat on the cam lobes. Even with perfectly machined angles, the worst-case rollers will scrub across 10% of the lobe's width during normal operation. If I were starting this project over, I'd look seriously into making the changes needed to reorient the lifters in the guide blocks and cam box as they were in the full-size engine.

Although I've purchased the tiny ball bearings specified in the drawings for the rollers, I'm having second thoughts about using them. As cam rollers these bearings will be worked hard and, if they don't ride flat on the cam lobes, the twisting forces created on their inner shafts could cause them to catastrophically fail and scatter tiny steel balls throughout the cam box and oil pump.

The necessary roller angle depends upon the particular lifter's location and according to the lifter drawing will be between two and four degrees. Since the Knucklehead uses a single cam to time the valve events in both cylinders, its .080" wide lobes shown on its drawing are only .050" apart leaving little room for the lifter bodies. In order to improve these clearances, the locations of the lobes for the front and rear intake pushrods were reversed in the drawing for the model engine's camshaft. This change assigned adjacent lifters to pushrods on opposite banks of the engine. Even so, the lifters don't have much material available to support the rollers' .040" diameter shafts. Canting the rollers in the ends of the lifters will require removing precious material from their ends around the rollers and will weaken them even further.

Since I plan to eventually machine the camshaft as a 4-axis operation on my Tormach, I have some options when it comes to the contours of the cam lobe faces. Instead of conventional flat faces for flat rollers, I'm considering machining a radius'd groove into the face of each lobe that will be matched to a contour on its solid machined roller. This will eliminate the need to cant the rollers in the lifters and will distribute their loads over larger contact patches than I would have available with imperfectly machined shaft angles.

So far, no obvious problems with the scheme have jumped off the pages of my sketches but, being unconventional, I want to make a few concept parts so I can watch it in action before actually committing the camshaft to it. To this end, I machined some camshaft blanks that, although initially have only circular lobes, can be re-machined as needed. Their diameters are large enough to allow me to experiment with the groove idea but later turn them into final camshafts - either grooved or flat. If the contoured roller idea doesn't work out, I'll likely replace the ballbearings with hardened solid-turned equivalents and give the shaft angle machining my best effort. Another option that I plan to consider is to contour the rollers but use them on a flat lobed camshaft.

Before machining the cam blanks, I needed to know the exact locations of the lobe centers. To determine these, I turned a simple test shaft with a diameter equal to the expected average diameter of the final cam lobes and temporarily installed it in the camshaft's location. Using closely fitted rods with conically turned tips installed in all four pushrod positions, the centers of the lifter bores were transferred to the inked surface of the test shaft. These locations were then measured under a spindle microscope using my mill's DRO.

Centering the lobes under the centers of the lifters will leave only .035" gaps between .080" wide lobes instead of the .050" shown on the camshaft drawing. I assume, but can't be sure, that the distances on the camshaft drawing were intended to reflect the lifter centerlines. Looking for an error, I re-measured my lifter angles in the guide blocks but they matched the roller angles called out in the drawings for the lifters to within tenths of degrees.

Two complete blanks were machined from O-2 drill rod so they can be hardened after completion. In addition, I turned a third blank minus its cam gear mounting flange so I would have better visibility of the lifter during my initial experiments.

A blank for the brass cam gear was machined several months ago while I was making the other spur gears for the engine. It required only a final operation to attach it to the cam blank. The holes for its mounting screws were slotted so the final cam can be accurately indexed to the crankshaft. Without these slots, the 24 tooth cam gear would only provide 30 degrees of indexing resolution. - Terry


----------



## petertha

_hoped it would be completed by now so I could start work on the Offenhauser_
The Ron.C 270 design or something of your own creation?


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## mayhugh1

It will be Ron's...


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## doc1955

Very nice work every thing looks so nice!!!


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## RonC9876

mayhugh1 said:


> It will be Ron's...


A vastly improved version no doubt!


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## rodue

If time was money us model builders would be rich. I had a good friend when ask, how long did it take to complete that model he's answer was  a, " cold winter and a late spring"


----------



## mayhugh1

I couldn't put my finger on it, but something continued to bother me about the contoured cam in my previous post, and so I spent a couple days trying to create a working assembly in SolidWorks that would allow me to virtually test it. However, SolidWorks (or at least my version of it) can't mate cams and followers that have contoured surfaces, and every workaround that I came up with required changing the model in such a way to limit its usefulness. Along the way, though, I discovered a problem that I've shown in the drawings in the photos.

A lifter that's angled along the rotational axis of a camshaft will require its roller to move sideways across the lobe as the lifter moves up and down in its normal cam-following action. The problem is that this side-to-side motion won't be tolerated by the contoured cam/roller pair. The contoured cam and roller that I was considering could be designed to fit perfectly together at, say, the flank of the cam. But, as the lifter rides up on the nose of the cam, its roller will try to move across the lobe but will run into resistance created by the now misaligned contours between them. In the best case, the roller might make it up onto the lobe's contour but with a single point contact between them while loaded by the valve train. In the worst-case, parts will end up bent, broken or prematurely worn. To get around this, the end of  lifter would have to be opened up around the roller to allow the roller to slide sideways on its shaft so it can remain in its original position. Removing material in this area is what I was trying to avoid in the first place with the contours.

In any event,  I've decided to abandon roller lifters completely. The requirement to cant the rollers in the space available introduces too much complexity and will likely produce an unreliable result. Not only does each lifter require a uniquely angled roller, but the drawings also show that the lifters must be uniquely keyed to their positions with pins and slots in order to maintain the necessary orientations of the rollers on the cam. Contouring the cam and rollers is interesting but is really just moving the complexity around for little net gain. I have no doubt that after a lot of painstaking effort, the final result in either case would be no better than a simple contoured rod end and much less reliable.

During my breaks from SolidWorks, I put some throw-away work into designing and machining the now defunct rollers I had planned to use. For closure, I've included a couple photos of them as well. - Terry


----------



## tornitore45

Yap is all a matter of geometry. The lifter does not "lift".  It is constrained to move on its own axis and therefore as it rises it moves laterally, off the cam centerline.
Cams with roller lifter have flat flanks, cams with sliding lifters have arched flanks, are you redesigning the cam?   One possibility is to keep the roller straight (perpendicular to the cam axis) and have a hemispherical joint between lifter and push rod to accommodate the angle.


----------



## kvom

I assume that the amount of lift for each lobe is calculated vs. the angle of the lifter.  Or does it make a difference in a model?


----------



## mayhugh1

kvom said:


> I assume that the amount of lift for each lobe is calculated vs. the angle of the lifter.  Or does it make a difference in a model?


kvom,
Theoretically, it should. But as you say, it shouldn't make any difference in a model. - Terry


----------



## Rozlo

I've just read all 13 pages of this build to catch up and all I can say is Simply Awesome.  This is a work of art.  I would think it would take some serious time to machine without CNC.  Makes me want to go out and buy a CNC machine.  But not yet I'm still a beginner.   I will most definitely keep up with this build.  Thanks for sharing.


----------



## rodue

I was too cheep to purchase the bearings, so I increased the size to .25 and replaced it with drill rod roller  It dose great a problem on insulation but I have conquered that. I will have to see how well it works. I am going to have to add a spring to the push rod it doesn't want to return without help. As I said earlier a square broch I think would work better on the lift.


----------



## mayhugh1

Work on the lifters began by machining a set of guide bushings for them. These bushings provide bearing surfaces for the lifters inside the guide blocks and the roof of the gear box. They were machined from SAE-660 bearing bronze for smooth sliding fits with the lifters.

It's important that oil returning through the pushrod covers from the rocker boxes be allowed to drain quickly back into the gear box to avoid filling up the covers with oil. Four grooves were machined along the length of each bushing to facilitate this return. Three grooves were milled around the bushing's o.d., and one was broached through its i.d. Oil returning through the broached groove will lubricate the body of the lifter inside the bushing before finding its way (hopefully) to the cam. The bushings were dimpled for setscrews that will secure them to the guide blocks. They'll be positioned far enough below the top surfaces of the guide blocks so the ends of the pushrod covers don't interfere with the oil flow.

The lifters and lash adjusters were machined from O-1 drill rod. Both have wrench hex's machined into their tops as aids during valve adjustments. The drawings specify 6-32 for the threaded sections which didn't permit the use of jam nuts due to lack of space inside the pushrod covers. I reduced the thread size to 4-40 which allows the use of small pattern jam nuts. The tops of the adjusters were machined with polished hemispherical cups to accommodate the ends of the pushrods.

All four lifters are identical except for their integral tappets. Each was machined for either a two, three, or four degree crown depending upon its particular location. The locations were engraved into the flats of their hex's in order to avoid confusion during assembly. The CAD drawing shows the design of the 4 degree crown as an example, and a microscope photo shows the actual machined result. What would otherwise have been a pointed center was blended into the crown using a shallow contour. In order to provide wrench access when doing valve adjustments, the lifter length was selected so that while resting on the flank of the final cam, its hex will be just above the top surface of its guide block.

Some experimentation with tool selection and its feeds and speeds was done while CNC machining the tappets so they would come off the lathe with accurate and extra fine finishes that wouldn't require a lot of risky manual polishing. The process was tedious, but I was able to go from the lathe to 1500 grit paper before finishing with buffing compound. The lifters were quenched in oil after a one hour soak at 1450F and then tempered at 350F. (The cam will be tempered at 450F.) The lash adjusters weren't heat treated.

With the lifters temporarily installed in the engine in their bushings, I was able to check their contact patches (or more correctly, their contact lines) on the inked lobes of one of the cam blanks machined earlier. Theoretically, these lines should have been about .027" wide and located on the inside halves of the lobes. Measurements of the two and three degree lifters showed the widths to be between .020" and .026" and a little closer to the lobe centerlines than expected. The contact line for the four degree lifter was only .014" wide, but almost .005" of its missing width can be attributed to a geometry issue created by the excess starting stock on the cam blank. - Terry


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## Scott_M

That'll work !
Nicely done.
Terry your engineering skills are as impressive as your machining skills. You set the bar pretty high for the rest of us. This is greatly appreciated and shows what can be accomplished when you really give it your all.
Thanks

Scott


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## kvom

Any reason that the lifters wouldn't want to be centered on the cams?


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## mayhugh1

Scott, thanks for the comment. It's much appreciated.

Kvom, no reason that I can think of. After I get an actual cam machined that I'm happy with, I may make a new blank with the lobes repositioned. I'll want to see the contact areas on a finished cam before I do that, however.

Terry


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## tornitore45

Terry, what is the diameter of the hemispherical cavity?  What is the diameter of the push rod section impinging in the adjuster?

I have a similar situation in the Edward 5 radial.   The drawing calls for a 0.094 rod with 0.075 ball ends working into a 0.080 hemispherical cavity 0.062 deep.
On paper it looks wonderful but after machining such small features it "feels" like there is not enough captivity to keep the rods in place.
Your picture looks like the cavity is much more deep and "secure" than what I see on mine.


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## mayhugh1

Mauro,
The diameter of hemispherical cavities are .157" and they're .087" deep. The diameter of pushrod balls will be slightly under that. I haven't decided in the diameter of the pushrods themselves yet - probably .125" diameter though. - Terry


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## tornitore45

OK that explains it.  Much larger that the stuff I am dealing with.
I am toying with the idea of using a slender cone with round point into a conical hole to provide a deeper engagement for the same diameter.


----------



## mayhugh1

Harley's world famous irregular firing sequence is the result of using a single pin crankshaft in a 45 degree V-twin. The rear cylinder fires 315 crankshaft degrees (360-45) after the front cylinder fires, and the 4-stroke cycle completes with the front cylinder preparing to fire again after the engine rotates an additional 405 degrees (360+45).

Similar to the full-size Knucklehead, the model engine uses a single four-lobe camshaft albeit with different lobe assignments. The lifter block angle separations in the model are 46 degrees for the intake lifters and 56 degrees for the exhaust lifters. (These angles may be different from those in the full-size engine.) The intake lobes on the model engine's camshaft should therefore be separated by 111.5 camshaft degrees (315/2 - 46) since the camshaft rotates at 1/2 the speed and in the opposite direction to the crankshaft. Similarly, the exhaust cam lobes should be separated by 101.5 camshaft degrees (315/2 - 56).

An end view of the camshaft in the drawing in the download shows the intake lobes for the front and rear cylinders located suspiciously close together and likewise for the exhaust lobes. Accounting for the angles between the lifters, a little math shows the cam in the drawings will open both intake valves within 16 degrees of one another, and it will also open both exhaust valves opening simultaneously.

Unfortunately, the cam provided in the drawings isn't actually for a Knucklehead but instead provides an obscure 'Big Bang' timing that blends both cylinders into a single behemoth with roughly twice the volume. A V-twin configured this way will have a distinctively loud and hard pounding power stroke but most likely won't perform well with a single carb setup. The cam in the drawings also orders the valve events in such a way to cause the engine to run in a direction opposite to that of a Harley. Upon realizing this earlier in the build, I modified the designs of the oil pump and distributor and designed the starter clutch to work with the engine running in the proper Harley direction which is clockwise when viewed from the gear box side of the engine.

The 'Big Bang' cam provides intake valve lifts of .050" (.060" lobe lift x .84 rocker ratio) and exhaust valve lifts of .070" (.065" lobe lift x 1.08 rocker ratio). Since both valve seat diameters are .510", the lift-to-diameter ratio for the intake valves is .096, and for the exhaust valves it is .140. When valves have been properly sized for the needs of an engine, a lift-to-diameter ratio of .250 is generally considered ideal. At peak lift, it's the ratio that corresponds to equal face and gap areas which means lift isn't limiting flow. The Knucklehead's valves are probably larger than needed, and so throttling their flow with lift most likely won't be an issue. The model's maximum allowable lift to insure the engine remains interference-free with its original low compression pistons is .100", and so a replacement cam could possibly provide a bit more lift.

Harley's original Knucklehead cam specs are surprisingly difficult to find, but a number of aftermarket suppliers offer what they claim to be a 'stock' equivalent:

Intake (234 deg duration): opens 13 deg BTDC
closes 41 deg ABDC
Exhaust (240 deg duration): opens 44 deg BBDC
closes 16 deg ATDC

A widely available 'S' grind is also available from the aftermarket:

Intake (262 deg duration): opens 27 deg BTDC
closes 55 deg ABDC
Exhaust (262 deg duration): opens 55 deg BBDC
closes 27 deg ATDC

where I assume the 'S' stands for 'symmetric'. All these numbers are, of course, in crankshaft degrees.

Overlap, the crankshaft angle over which the intake and exhaust valves are simultaneously open, is an important cam spec because it controls the rpm range over which the engine will make its power. Rather than deal with a lot of opening/closing angles when comparing cams, the lobe separation angle (LSA) is often used instead. LSA can be calculated by subtracting the overlap from the average of the cam's intake and exhaust durations and then dividing the result by two in order to express it in cam degrees. A rough dividing line between mild and wild is an LSA of 110-112 degrees. Both of the above cams happen to have LSA's of 104 degrees which, surprisingly, is on wild side.

The next step is to come up with a suitable replacement camshaft for the Knucklehead. The goal is a design that correctly compensates for the model's lifter block angles and produces an engine running in the proper direction with conventional 315/405 Harley timing. - Terry

note: when comparing the camshafts in the two photos, remember they were designed to turn in opposite directions.


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## mayhugh1

For a 'mostly display' model engine, I'd tend to avoid camshafts with large overlaps and narrow LSA's that are responsible for poor idle quality and high rpm power bands. My goal for the Knucklehead's cam is an easy-to-start engine capable of low rpm idling. It needs to make only enough power to overcome its own losses if that means minimizing the amount of generated heat. For my cam I've decided upon a small overlap in order to maximize manifold vacuum for improved starting and idling. I also plan to open the exhaust valve a little earlier than normal to make the engine a little louder. At the expense of some power, it might help the engine shed heat through the exhaust for longer run times. My target specs are:

Intake (225 deg duration): opens 5 deg BTDC
closes 40 deg ABDC
Exhaust (250 deg duration): opens 65 deg BBDC
closes 5 deg ATDC
intake lobe lift: .090" (.075" @ valve)
exhaust lobe lift: .070" (.075" @ valve)

The lobe separation angle for this cam works out to be 114 degrees which puts it in the mild category.

For verifiable measurements, a specific lift at the 'open' and 'close' angles needs to be specified. Full-size cams are always specified this way with .020" and .053" being typical for motorcycle cams. Since there doesn't appear to be a standard for model engines (zero is used as often as not), I've selected .004" lobe lift to define the 'open' and 'close' angles for my cam.

When designing a cam lobe, the angle between the starting points of the lobe's ramps needs to account for the lift used to specify its duration in crankshaft degrees. In order to determine these points, I used a virtual cam tester that I created in SolidWorks specifically for the Knucklehead.

The tester was designed to work with the CAD/CAM model that will eventually be used to machine the camshaft so measurements can be made as though the actual cam was operating inside the actual engine. A degree wheel, attached to a virtual crankshaft, is geared to the camshaft under test. Lifters operating at angles matching those in the actual engine ride on the cam's lobes just as they will inside the engine. I began work on the tester while still planning to use roller lifters. I didn't bother modifying it after shifting to non-roller lifters since the differences between the two in the tester appears to be insignificant. Although I couldn't figure out how to make 'live' measurements inside a SolidWorks assembly, the lifters can be individually measured with respect to a reference surface and their precise lifts recorded for any crankshaft angle.

The tester's small red arrow is a reference pointer for the degree wheel that can be moved anywhere around its circumference. The 315 degree outer collar can also be independently positioned around the degree wheel and used to indicate the relative locations of the tester's virtual cylinders in crankshaft degrees. My original reason for creating the tester was to have a tool to sanity check the dizzying compensations that will have to be made to the angles between the cam lobes to accommodate the unequal angles between the intake and exhaust lifters.

Using the tester to iteratively design the cam's intake lobes eventually showed the angle between the starting points of the lobe's ramps had to be 127 degrees to obtain a crankshaft duration of 225 degrees at .004" lobe lift. This was found by measuring the angles on either side of the lobe's center where the lift measured .004". The actual angle between the lobe's ramps was increased in small steps until the specified duration was finally achieved. A similar procedure was used to design the exhaust lobe. Final dimensioned drawings of both lobes are shown in the photos.

After the contours of the intake and exhaust lobes were defined, their angular positions relative to one another needed to be determined. Since the intake lifters are 46 degrees apart, the cam will be machined so the centers of the intake lobes are 111.5 degrees apart (i.e. 315/2 -46). Since the exhaust lifters are 56 degrees apart, the exhaust lobe centers will be 315/2-56 = 101.5 degrees apart.

The final angles needed to complete the cam design are the separation angles between the lobes of each intake/exhaust pair. For this engine, these are somewhat tricky. If the angle between the intake lifters were identical to the angle between the exhaust lifters, both separation angles would be the cam's LSA or 114 degrees. Since the angle between the exhaust lifters is 10 degrees greater than the angle between the intake lifters, this difference will alter the separation angles.

While standing on the gear box side of the engine with the camshaft rotating CCW, the rear exhaust lifter is located 5 degrees past the rear intake lifter. This 5 degrees must be added to the required LSA when computing the required angle between the rear intake and the rear exhaust lobes (i.e. 114 + 5 = 119 degrees). The situation is reversed for the front lifter pair. In that case the front intake lifter is located 5 degrees past the front exhaust lifter, and this 5 degrees must be subtracted from the required LSA when computing the required angle between the front exhaust and front intake lobes (i.e. 114 - 5 = 109 degrees). With these compensations applied to the virtual camshaft, the LSA measured 114 degrees for both the front and rear virtual cylinders in the tester.

One last angle of importance, the centerline angle, isn't needed for the camshaft's design nor its machining but is required to install and time it to the crankshaft. The intake centerline is the point of highest lift on an intake lobe. The centerline angle, illustrated in one of the photos, is the number of crankshaft degrees between the intake centerline and its cylinder's TDC. Either the front or rear intake lobe and cylinder TDC can be used. For my cam, I'll set the centerline angle of the cam's front intake lobe 107.5 degrees (225/2 - 5) past the front cylinder's TDC. The rear cylinder can just as easily be used.

The camshaft can be slightly advanced or retarded by altering its centerline angle a few degrees during installation. This can make a small change to an engine's performance which can be of interest to a performance enthusiast. The slotted mounting holes in the cam gear provide for this, but my plan is to install the cam 'straight up'.

Timing the virtual camshaft to the tester's virtual crankshaft is relatively simple. The crankshaft with its attached degree wheel is first rotated to the point of maximum lift of the front intake lifter. This is the center of the front intake lobe's duration and is tagged by setting the red arrow next to the zero degree point on the degree wheel. The outer collar is then rotated until the front TDC arrow is 107.5 CCW degrees behind the red arrow. Then, as the crankshaft is rotated, the virtual cylinders (indicated by their arrows on the collar) will reach their TDC's whenever the degree wheel's zero passes under their respective TDC marker.

The next step is to finally machine the actual camshaft. The last photo in this post contains a worksheet that will be used to do the machining. The angles as they're displayed in the worksheet are more suitable for machining the camshaft than for understanding where the angles came from. For completeness, a follow-up photo shows the pertinent angles between each lobe. - Terry


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## mayhugh1

One more photo ...


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## brotherbear

Terry
Once again I am compelled to thank you for the time and energy you so freely give the effort to explain your process in a concise understandable way with illustrations, photographs, and thought-provoking dialogue. Without any pretense of hubris, you explain what you are doing what your concerns are, how and when to address those concerns. With an uncompromising skillset, you unashamedly construct jigs, clamps, sacrificial hold-downs and consistently machine multiple parts. Your willingness to share the ocasional error and reconstruction or altered fabrication process. 
I have gone from immediately reading your posts to making a note of...and setting aside some time when I can have a cup, sit down and visit Terry's shop, see what he's been up to and learn something as well as just enjoying such quality of workmanship. 
Thank you for sharing your efforts with me!


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## minh-thanh

brotherbear said:


> Terry
> Once again I am compelled to thank you for the time and energy you so freely give the effort to explain your process in a concise understandable way with illustrations, photographs, and thought-provoking dialogue. Without any pretense of hubris, you explain what you are doing what your concerns are, how and when to address those concerns. With an uncompromising skillset, you unashamedly construct jigs, clamps, sacrificial hold-downs and consistently machine multiple parts. Your willingness to share the ocasional error and reconstruction or altered fabrication process.
> I have gone from immediately reading your posts to making a note of...and setting aside some time when I can have a cup, sit down and visit Terry's shop, see what he's been up to and learn something as well as just enjoying such quality of workmanship.
> Thank you for sharing your efforts with me!


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## kvom

I was wondering whether the plans included specs for the cam, and if so did you use these as starting points for refining to your own preferences?  Otherwise I'd think very few people could even attempt this build.


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## mayhugh1

Kvom,
The plans include specs for a "big bang" cam that fires both cylinders on top of each other and runs the motor backwards. My camshaft, which is intended to run the engine like a Harley, was designed from scratch. I don't know why that cam was used, but I'm not sure that it's the reason why the engine hasn't been attempted by more builders since most wouldn't have realized the issue with it until well into their build. I'm trying to include enough information about mine, though, so others can use it if it actually ends up working as I hope.

The real reason for the engine's lack of popularity is probably its complexity. This has been the most challenging engine I've work on to date which really hasn't been a big surprise to me. The original designer did an incredible job coming up with the plans - a feat I couldn't begin to match. But nothing this complex could be expected to be gotten entirely correct without an actual build or two to debug the paper. It's been identifying and coming up with fixes for all those issues that I've run into that has been so time consuming and something that I appreciate many others aren't interested in doing. -  Terry


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## kvom

mayhugh1 said:


> This has been the most challenging engine I've work on to date


Even after the Merlin?  wow.


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## petertha

_ Terry> A rough dividing line between mild and wild is an LSA of 110-112 degrees. Both of the above cams happen to have LSA's of 104 degrees which, surprisingly, is on wild side..... The lobe separation angle for this cam works out to be 114 degrees which puts it in the mild category..._

I really like your useful tutorial on cams & especially how you simulated the settings in CAD. Thanks for laying it out, its not exactly an easy subject (at least to me).

- Are the gears more for visual or you are also evaluating mechanical attributes? ie. presumably have a numerical gear ratio defined in the motion mates & they could be 2 circular discs for that matter. Or are you actually registering a cam reference point to a tooth reference or figuring out mechanical gear size & tooth pitch etc.?

- I adopted the LSA calculation into my own spreadsheet tool. Just curious - did you ever calculate out what your radials worked out to for comparison? I am getting a low number like 96 deg on this particular (methanol glow) engine. Are the guideline numbers you reference above suited to a particular engine type or maybe influenced by the type of fuel they burn?


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## mayhugh1

Pertetha,
The gears are there just because they're in the actual engine. It was a convenient way of getting the proper direction and speed of the camshaft with respect to the crankshaft. In the tester, I was trying to duplicate the engine as closely as possible because I needed a sanity check on the lifter compensations that were making my head spin. In use, the gears do get in the way of measurements sometimes, and I often 'hide' them using a feature of my CAD that allows one to look through selected components while retaining their functionality.
I never checked the LSA of any of my other engines. If I remember correctly, there wasn't much if any at all overlap in the radials, and so I would expect their LSAs to be fairly high. Also, all my comments were for a four stroke sparkplug engine. I've no experience with glow plug or two stroke engines and would have to some thinking about what, if any changes, would have to be made for them. - Terry


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## mayhugh1

The CAM software that I use (Sprutcam) has a four axis 'Rotary Machining' operation that's capable of machining camshafts. This particular operation first appeared in my now nearly decade old version of the software, and it was Sprutcam's first continuous 4-axis machining operation. Although probably much improved by now, its initial features were limited, buggy, and not well integrated into the software's framework. After considerable trial and error, I was able to use it to machine the Merlin's camshafts and the counterweights on its crankshaft. I'm still a rank user, but with my Merlin's notes as a starting point, I was soon simulating the two machining operations needed for the Knucklehead's cam.

I used an earlier made practice blank to fine-tune the operations' parameters in actual metal. A problem that's shown up in the past are crowned lobe surfaces created by the dished relief ground into the bottoms of cylindrical end mills. I got around this on the Merlin by having a local tool grinder remove the relief on a couple of my cutters especially for use with this operation. The relief on a stock 1/8" .010" corner radius'd carbide cutter that I had on hand seemed almost insignificant, and so I decided to use it 'out of the box'.

Each lobe was machined using a .005" depth of cut and an effective feed rate of .5 ipm. This feed rate is considerably slower than one would expect for an 1/8" carbide cutter working in a piece of drill rod, especially with such a shallow depth of cut. However, one of the bugs I've come across in this particular operation is an inverse time feed rate miscalculation for certain cutting moves under certain conditions that tend to chip cutter teeth.

The setup that I used required initially positioning the spindle over the center of the lobe to be machined and then lying to the software about its location. The lobe was machined using only z and y axis spindle moves while the rotary turned some 30 continuous revolutions below it. The machining marks left on the part as it came off the mill look much worse in the microscope photo than they actually are. They, along with any visible traces of a crown, were easily removed with 1500 grit paper.

Although the software is capable of generating code to machine all four lobes in one continuous operation, I machined them one at a time and manually reset the rotary and repositioned the spindle after each. Although unfounded, I was concerned about running into some obscure Mach 3 bug caused by the tens of thousands of degrees that would have accumulated on the rotary.

Both previously prepared cam blanks made it all the way to becoming finished camshafts, and so I ended up with a spare for my keychain. After an hour at 1465F they were quenched in oil and tempered at 365F. To prevent scaling during the high temperature cycle, the parts were enclosed in argon-filled stainless steel foil bags closed with double-folded seams.

Both cams were trial-fitted inside the engine and the lifter contact point locations verified with a dental mirror. With the lobes finally at their proper diameters, all lifters appeared to be riding on their lobes where they should be. With finger pressure on the lifters, the follower motions on the lobes of both cams felt silky smooth. One cam was selected for use, and a spacer between it and the gear box cover bearing was machined to remove the camshaft's thrust clearance.

I've included some photos that may be of interest. My next step is to machine a set of pushrods. - Terry


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## tornitore45

What provision do you have to phase the cam to interpolate between gear teeth?


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## mayhugh1

tornitore45 said:


> What provision do you have to phase the cam to interpolate between gear teeth?



See the photos in post #233


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## tornitore45

I see the gear is pretty busy.


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## mayhugh1

At 5/32" diameter, the relatively short (2-1/2") pushrods in the Knucklehead drawing package are pretty substantial. Even though I'd planned to use smaller diameter pushrods, I kept the 5/32" for the machined sockets in the 7075 rocker arms to take advantage of the wear resistance it would provide. Smaller diameter rods should look a little better, have less mass, and speed up oil return inside the pushrod covers. There will also be some extra wiggle room for the rods inside the covers.

Before machining them, I wanted an accurate measurement of each pushrod's maximum allowed length. There's easily enough range in the lash adjusters so the rods can all be made identical, but the covers provide only limited access for their adjustments. Customizing the length of each pushrod to its particular location will insure the adjusters stay inside their access windows.

In order to determine the lengths, I made an adjustable pushrod to use as a measuring stick. After cutting a set of four pushrod blanks to the lengths measured (minus .015"), spherical ends were machined on each. The diameters between the ends were turned down a bit at a time after inching the rods out of the lathe collet, but to remove the last quarter inch or so, the part had to be flipped around. A couple layers of shrink tubing over the already turned-down areas provided remarkably low TIR (.002") surfaces for the collet to grip while removing the remaining material.

It came as no surprise that I'd have to make yet another degree wheel. I've not been able to come up with a 'one fits all' design, and I have almost as many degree wheels laying around as I have completed engines. The Knucklehead's version is attached to the engine using a machined Delrin center section that's finger-pressed into a recess in the flywheel.

While thinking through the process of timing the camshaft, it occurred to me that a screwdriver slot in the end of the camshaft might be useful for fine tuning the the cam in its adjustable gear. The slot would have been a lot easier to machine before the cam was hardened, though. After rubbing the teeth off a HSS slitting wheel, I remembered about the heat treatment and set up a tiny abrasive wheel in the mill to grind the slot. After completing it, I really didn't find it all that useful.

Camshaft timing began by rotating the flywheel until its TDC mark was adjacent to the 'F' mark on the crankcase. As explained much earlier, the alignment of these two marks indicates the front cylinder is at TDC. While standing on the gearbox side of the engine with the degree wheel attached to the flywheel, a stationary pointer was set up adjacent to a convenient angle on the degree wheel whose value was recorded. The goal was to install the camshaft so the center of the front intake lobe occurred 107.5 degrees after the front cylinder's TDC. As mentioned earlier, this 107.5 degrees is the cam's centerline angle. This relationship with the cam's centerline insures fuel will be sucked into the front cylinder during the piston's downstroke. From the gear box side of the engine, the crankshaft rotates CW when the engine is running. The cam must be installed so that when the degree wheel is rotated 107.5 degrees CW from its recorded position, the front intake lifter is sitting on the center of its lobe.

On this particular engine, determining the center of the intake lobe requires only the front intake lifter (no pushrod) to be installed. With its lash adjuster temporarily replaced with a machined-flat screw for use as a DTI measuring surface, a very sensitive indication of the lobe's center is available. The cam's position was quickly determined to within a single gear tooth, but this was only good to some 30 crankshaft degrees. Using the slotted gear to resolve it further was much more tedious and seemingly chaotic, but I eventually managed to land on 108 degrees.

Using .004" lobe lift points, measurements using the same DTI setup showed the front intake opening 4 deg BTDC and closing 30 deg ABDC compared with the 5 deg and 40 deg target values. Similar measurements on the rear intake yielded 4 deg ATDC (not BTDC) and 39 deg ABDC.

Measurements on the front exhaust lifter showed it opening 65 deg BBDC and closing 4 deg ATDC compared with target values of 65 deg and 5 deg. The angle between the front and rear intake lobe centers was measured to be 322 degrees compared with its target value of 315 degrees.

Using half the distance between the .004" lift points to define the lobe centerlines gave a slightly different result, but it wasn't at all clear it was any better than measuring the lobe peaks. After making my peace with the measurements, the five mounting screws in the cam's slotted gear were torqued down for the final time.

The crankshaft gear is fixed to the crankshaft using a pair of dowel pins whose holes were cross-drilled in such a manner to insure the two can be assembled in only one way. With the timing completed, witness marks added to the crank and cam gears will now indicate the cam's proper installation during final assembly.

I thought I'd now be ready to machine the last parts needed for final assembly - the piston rings. However, after machining the pushrods, I ran into a problem I should have realized earlier: it's not possible to install a pushrod simultaneously with its cover without significant engine disassembly. Either can be installed separately but not together. My cover design needs to be changed so the lengths can be shortened another 3/8" while they're being installed with a pushrod inside them.- Terry


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## Scott_M

Hi Terry
Bummer on the push rod tubes !
Question ?
If you have not made the rings yet then I am assuming the whole top end needs to be disassembled to install them. Is that not sufficient to get the rods and tubes in place ?
Or is it because "it is just not right " Which I totally understand 
Or will you not have enough room to set valve lash with the pushrod tubes fully collapsed ?

Scott


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## mayhugh1

Scott,
The top end will have to come apart to install the rings, but I just don't like the idea of the pushrods getting captured during the reassembly. Like you say, it's just not right. - Terry


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## Scott_M

"It's just not right"   I kind of thought that was why 

And I forgot to mention, as always , beautiful work !

Scott


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## rodue

I  was studying you plans on the carburetor and I didn't see the float, did you do away with it. The float is a problem to make it light enough to float in fuel. I am eager to see your engine running. Rodue


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## mayhugh1

rodue said:


> I  was studying you plans on the carburetor and I didn't see the float, did you do away with it. The float is a problem to make it light enough to float in fuel. I am eager to see your engine running. Rodue



Instead of a float, I'm using an electric fuel pump located inside the fuel tank to drive a recirculating loop that will maintain a constant level of fuel in the carburetor bowl. - Terry


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## michelko

Oh man... this is realy a piece of art!!! Awesome work.

Michael


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## mayhugh1

Salvaging my original pushrod covers seemed hopeless, and so I spent a few days looking at totally different cover designs. These all wound up as dead ends, and so I took a few days off to reset my thinking. Eventually, I returned to my original design with some modifications that looked promising even though I still couldn't reuse any of the existing parts.

The new upper covers are similar to the old ones including the Kynar oil seals. Of the three parts making up a complete assembly, the top halves are still the more interesting pieces and relatively straightforward to machine. The lower halves should have been trivial to make, but I made things difficult by making their o.d.'s as small as possible. After some trial and error, I found I could safely reduce their wall thicknesses to as little as .010" over the roots of their internal threads. I initially tap-threaded a few parts after profiling their o.d.'s, but manual threading invariably caused the finished parts to swell as much as .003". This created clearance problems for the close-fitting center covers that will have to freely slide over them.

The solution, of course, was to thread the lower covers before profiling their exteriors, but the resulting thin-wall parts with their unfortunate shapes had too much stick-out and created severe chatter and surface finish issues. My goto solution for this problem is to pack the part with modeling clay, but this time it didn't help. The chatter was eventually squelched by threading a short piece of loose-fitting threaded steel rod inside the part to absorb the oscillations while its exterior was being turned.

The center cover is also an internally threaded thin-wall part. However, being turned from stainless steel, and having only a few internal threads, there was no noticeable o.d. distortion. The center and upper covers were permanently joined together with a grease-stick type thread locker that reduced the three part cover assemblies to two parts. This was done to make their installations a little easier, especially in the limited space around the intake lifters.

The machining steps for all three parts took some time to get just right, and in the process I wound up making several extra sets. I still don't feel comfortable about permanently joining the center and upper covers, but trial installations in the engine showed it provided some welcomed advantage. Before assembly, the aluminum-on-aluminum threads were dusted with powdered graphite for a butter smooth fit.

The larger lash adjustment windows available with the new covers no longer require the pushrods to be sized to their particular position in the guide blocks, but I plan to use the ones I've already made. To wrap up the pushrod/cover work, I also cut a pair of teflon gaskets to seal the guide blocks to the gear box. The photos show the new covers and some comparisons of them with the originals. - Terry


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## mayhugh1

I use George Trimble's method to make my piston rings. Although the multi-cylinder engines that I've been building have brought my to-date total up to some 200 rings, I seem to learn something new with every batch I make. The only change I've made to his process is to use a normalization temperature of 975F rather than his originally recommended 1475F.

As part of my own process, before any ring is installed on a piston, I check its fit in a cylinder using a 250 lumen flashlight. This test weeds out marginal rings before they wind up inside an engine. A ring that has any light leaking between it and its cylinder wall, other than through its running gap, is discarded.

My yields have generally been dismal because of circularity issues that typically show up during the blank's machining. I use class 40 gray cast iron from a number of sources that's been laying around in my shop for years. The errors have been unpredictable, seemingly uncontrollable, and sometimes as high as eight tenths over portions of the finally finished blanks. Typically, less than half of any blank will pass my acceptance criteria of two tenths, and occasionally an entire blank will be scrapped. Once the rings have been parted off, they're nearly impossible to evaluate until fully finished and light tested. After slicing candidates from the well-behaved portions of the blanks, my yields for the rest of the ring-making process are typically 80%-90%.

To start a large batch of rings, I usually prepare several blanks from different sources. Since I needed only four rings plus a few spares for the Knucklehead, I started a single blank from material that I'd used before. The Knucklehead's rings require a 1.0632" final o.d., and so I started with 1-1/4" diameter raw material. Cast iron rounds are manufactured oversize, and even though I might have gotten away with a smaller starting diameter, I'm leery of the castings' outer 1/8" or so.

A 4" drop was turned down to 1.109" so it could be held in a collet during the blank's machining. The blank was drilled through .625" and a portion of one end bored out to the rings' final i.d. This left a quarter inch wall thickness for work-holding and about .050" of o.d. stock for later removal. The blank was then heated to 700F for three hours and allowed to slowly cool overnight in hopes of removing residual stresses. (I began including this heat soak step a few years ago to combat an occasional issue I noticed with the blanks continuing to change dimensions days after their machining had been completed.) Two days later, the blank's o.d. was finished and polished to its final diameter plus two tenths using 800 grit paper. During its machining, quadrature measurements of the blank's diameter were continually recorded along every half inch of its length.

To my surprise, the errors never exceeded a tenth or so. This totally unexpected outcome may have been the result of finishing the blank's i.d. before the heat soak. In the past, I've left equal amounts of i.d. and o.d. stock on the blank for removal afterward.

Rather than waste the material, I decided to finish all 24 rings that I was able to slice from the blank using a .019" wide carbide parting insert. Parting tends to raise burrs on the corners of the i.d.'s, and these were broken using a 1/4" diameter ceramic file. The rings were parted a thousandth over the width of the ring groove. Using 600 grit grinding grease on a glass plate and a simple fixture to hold onto the rings, both sides were equally lapped to obtain a .001" ring groove clearance. During combustion, one of these surfaces will end up sealing against the lower wall of the piston groove and provide an important component of the combustion chamber's overall seal.

The Trimble article emphasizes the need for a straight radial break in each ring to properly contact with the spreader dowel, and a shop-made cleaver is recommended. Although 'good enough' results might be obtained by simply snapping the rings, I constructed a cleaver several years ago. After lapping, each ring was cleaved in preparation for heat treatment.

The Trimble articles also describe the construction of the fixture required to support the rings during their heat treatment. Equations were provided for the dimensions of a mandrel and a spreader dowel that are its key components. The fixture isn't difficult to make, but its dimensions are specific to a particular ring diameter, and this one will wind up in a drawer along side the other three I've made.

Although I've typically turned these fixtures from free machining alloys such as 12L14 or 303 stainless, this time I used plain hot-rolled steel. I always seal the fixture'd rings in an argon-filled stainless bag for protection during heat treatment, but the contents invariably wind up covered in a mysterious deposit. Although it isn't difficult to remove, it's an annoying extra step that I've begun suspecting may be related to the sulphur and lead that are alloyed into the free-machining steels I've been using. - Terry


----------



## petertha

Thanks for summarizing everything Terry. The sketch & worked through example was particularly useful as I see I misinterpreted one of the clearance parameters from your 18-cyl build.

BTW all, OLM now sells Durabar cast iron.
https://www.onlinemetals.com/en/search/results?text=cast+iron
I'm not sure if its because this CI its a recent add or their new website teething pains but I see round solid rod available as typical hobbyist cut lengths (ie stock for liners & rings). But some of the other shapes only appear as stock (long) lengths, so might have to inquire on that stock.


----------



## petertha

Terry can you elaborate on these insert blocks on the side of the slot. I thought maybe something like adjusting gib sliders but I don't see a set screw or anything.


----------



## petertha

One parameter I didn't see was running gap. If I understand, you make a cleaved split in the ring (call that a zero width kerf). Then the heat set over the calculated dowel diameter. Then you remove some additional amount from the open ends that would yield the running gap once compressed in the bore? If so how much & is that also a formula based on bore or something?


----------



## mayhugh1

petertha said:


> Terry can you elaborate on these insert blocks on the side of the slot. I thought maybe something like adjusting gib sliders but I don't see a set screw or anything.


Petertha,
They're just filler shims used to precisely align the cutting tips of the two HSS blades. 

Terry


----------



## mayhugh1

petertha said:


> One parameter I didn't see was running gap. If I understand, you make a cleaved split in the ring (call that a zero width kerf). Then the heat set over the calculated dowel diameter. Then you remove some additional amount from the open ends that would yield the running gap once compressed in the bore? If so how much & is that also a formula based on bore or something?



Peter, 
The running gap must be put in after the heat treatment. I generally use .004", which is more than enough and not at all critical. It's just there to make sure the ring doesn't close up and bind in the cylinder due to temperature expansion. I did the calculations for a previous build and found, contrary to popular opinion, it isn't a noticeable leak.  - Terry


----------



## Rustkolector

Terry,
Thanks for your comments and details on the Trimble ring making procedure. I have carefully built the same ring cleaver that you use and I consider the ring  breaks created as very straight radial breaks, but only at the surfaces contacted by the knife points. Between the knife contact points the break surface is rather jagged, and occasionally has a few protruding points. Enough so that it looks like the break surface needs a few strokes with a fine file (which I give them) to give a more even and square contact with the fixture dowel. What do your cleaved surfaces look like?
Jeff


----------



## petertha

Be interested in Terry's reply too. I haven't gotten that far yet, but in my simple mind I think an irregular break left untreated is equivalent to using a larger heat set dowel diameter. If you had some means of knowing how much this is, one might be able to guess the net effect relative to Trimble plot. But I would assume stroking it with a perpendicular file would be better than nothing within reason?


----------



## mayhugh1

Jeff,
Here's a photo of a couple gaps. These rings were just now taken out of the furnace and the running gaps haven't yet been filed. I looked at all 24 of them and they were identical to the ones in the photo.

I ground very sharp corners on the HSS blades of my cleaver and then used shims to insure they were perfectly aligned. In use, only the two sharp corners of the blades contact the ring, and I can feel a definite snap when the ring breaks without it twisting. - Terry


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## mayhugh1

And here is a reject untreated ring that I just found in the trash and just now


 re-cleaved. - Terry


----------



## mayhugh1

The rings were heat treated at 975F for three hours and allowed to cool overnight. In comparison with what I can remember about previous batches, this one came out looking pretty clean. It could very well be that the free machining steels I've been using in the past for the fixtures have been responsible for those annoying surface deposits. Before removing the rings from the mandrel, their collective o.d.'s were burnished with a white Scotchbrite pad. Burnishing didn't remove any metal - it just brighten the oxidized surfaces left behind by the heat treatment.

The extreme heat, along with the pressure exerted by the mandrel on the ring stack, caused the lapped surfaces of some of the rings to stick together. After sliding them off the mandrel, a few had to be separated with a razor blade. Starting at the gaps to avoid damaging important surfaces, they were easily worked apart.

With the rings separated, a .004" running gap was filed into each using a thin diamond file. These inexpensive files leave smooth surfaces on cast iron without magnetizing it. With the ring inside a simple shop-made gage, its gap could be checked with a feeler gage. The exact gap isn't critical since its only purpose is to prevent thermal expansion from binding and breaking a ring inside its cylinder. The gap is an insignificant leak especially since most of it is sealed off by the lower wall of the piston groove. Even at a couple extra thousandths, the leak it presents is equivalent to a circularity error of only micro-inches.

After gapping, the sides of the rings were briefly lapped for a final time using 1000 grit compound. The fixture used in this step gripped the rings around their o.d.'s rather than their i.d.'s as was done during the pre-heat lapping. When completed, the rings were thoroughly cleaned in lacquer thinner.

The final step in the ring making process was the light test. A photo shows the components of the fixture used to adapt a bright (250 lumen) miniature flashlight to the bottom of one of the Knucklehead's cylinders that was used to test the rings. Each ring under test was supported by its own spring force inside the cylinder about 3/8" from its top. At the beginning of each test, a close-fitting shouldered Delrin plug was inserted into the ring through the top of the cylinder in order to close up its center. The o.d. of the plug was .020" under the cylinder's bore to allow light leaking between the ring and cylinder wall to be easily seen from the top of the cylinder. The tests were done in a totally dark room with the flashlight held vertically in a vise.

It's extremely important for the ring to be positioned squarely inside the cylinder during its test. Even a perfect ring tilted inside the cylinder will make contact with the wall as an ellipse and pass enough light to fail the test. To insure the rings are positioned squarely inside the bore, a close-fitting Delrin rod was faced and used to push them up through the bottom of the cylinder and into position for their tests. The diameter of the rod was just .003" under the cylinder's bore to insure its own face was square to the bore.

My criteria for a good ring was for no light to pass between it and the cylinder wall. Out of 25 rings tested, 14 met this criteria. Five rings had obvious leaks that presented as prominent crescents, and these were discarded. Six rings had just a wisp of leakage and in all honesty might have been 'good enough'. These were labeled 'marginal fails' and saved for some future use. I've included representative photos of all three test results. The final post heat-treat yield turned out to be 56% compared with 70% for the Merlin build. - Terry


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## stragenmitsuko

truly amazing ! love this thread


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## propclock

Very informative, my rings are made the same way but, not light tested.
They will be in the future! I just assumed they will"break in".
And in fact after much running the surface of the un tested rings show
uniform wear on their O.D.'s . But break in did take a while.
Thanks for your wonderful posts.


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## kuhncw

Terry, thank you for the detail on your ring making process and especially your light-tight testing setup.

Chuck


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## petertha

Terry, so you are doing the light test on the same reference liner, right. Not finding a ring that matches a particular liner & keeping them paired?
If so, in your high cylinder count)engines, what kind of +/- bore accuracy were you satisfied with so that rings could be considered interchangeable coming off the light test apparatus?


----------



## mayhugh1

petertha said:


> Terry, so you are doing the light test on the same reference liner, right. Not finding a ring that matches a particular liner & keeping them paired?
> If so, in your high cylinder count)engines, what kind of +/- bore accuracy were you satisfied with so that rings could be considered interchangeable coming off the light test apparatus?


Petertha,
I used one the of the actual cylinders for all the tests. I lap my cylinders to a tenth of one another, or at least what I believe to be a tenth using the bore gage and micrometer that I use. Realistically, my repeatability is probably only a couple tenths or so. I lap all the cylinders as a group, opening each one up only one or two tenths at a time so they are all at the same diameter as they cross the finish line together. It's time consuming because of all the additional cleanings and measurements, but it avoids one ring from overshooting the target and then having to open up all the others to match. - Terry


----------



## mayhugh1

While machining the pistons last August (post #108), I made two sets: a high and a low compression pair. I've decided to use the low compression pistons since they'll present less of a load to the starter motor. Although it wasn't necessary, I machined 'eyebrows' into them for a bit more valve clearance. Even at their mild 5.3 compression ratio, the edges of the engine's huge valves come uncomfortably close to the hemi-topped pistons. After installing rings on them it was time to begin final assembly.

While re-installing the cylinders, I decided to replace the small pattern 10-32 nuts that I had been using to mount the cylinders to the crankcase and the heads to the cylinders. It was a nit-pick, but the nuts I was using never looked at home on the engine. I spent a day machining a couple sets of flange nuts that are not only more appropriate but provide a few more threads. After bead-blasting, they were painted black with baked-on Gun Kote so they'd blend in with the blued cylinders.

Another last minute but much more significant change was to replace the bolts in the rocker boxes with studs. In the original design, these bolts not only secure the covers to the rocker boxes, but they're also the shafts for the rocker assemblies. I finally realized that because the heads of the bolts are on the outsides of the rocker box covers, a lot of disassembly was going to be required to merely verify the rocker boxes are properly receiving and draining oil. All four of the 4-part rocker arm assemblies were going to have to be pulled in order to remove the covers, and this means the pushrod assemblies would have to be removed as well.

Both ends of the studs were drilled/tapped for 5-40 setscrews that were installed with permanent thread-locker to provide wrench-able hex sockets. The studs not only allow the covers to be removed without disturbing the rocker assemblies, but they also simplify installation of the pushrods and covers.

I wanted to duplicate the signature acorn nuts I've seen on the rocker boxes of the full-size engines. I was about to machine my own when I located some already polished stainless acorns of the correct size in my collection of scrap fasteners. The only problem with them was that they were threaded 1/4-20 instead of 10-32. Since there was no room for a threaded adapter, I bored the nuts out for plugs that were pressed, Loctite'd, and pinned into place. After threading the plugs, I made a set of teflon gaskets to seal them to the covers.

Another loose end involved sealing the four valve box covers. These covers have extremely narrow mounting flanges with lots of mounting holes and aren't well suited to a conventional gasket. I didn't want to use a messy sealer, so instead I used this vinyl sheeting that I found in a local craft store:

https://www.amazon.com/Oracal-Gloss...teway&sprefix=oracal+651+vinyl,aps,183&sr=8-6

It's 2.5 mils thick, adhesive-backed, and intended for making rub-on stencils. Its adhesive probably won't stand up to fuel or to significant heat. But, in this particular application as a gasket completely sandwiched between two machined surfaces, it should be satisfactory. After cleaning the covers with alcohol, they were set down onto the adhesive side of the sheet so the material could be trimmed from around their peripheries using an Xacto knife. Working from the non-adhesive side, the holes were cut remarkably clean using a chucking reamer held in a pin vise.

The gearbox assembly began with the installation of the oil pump and camshaft. The pushrod/cover assemblies were then installed and the valve lash set. I used the doweled plexiglass fixture plate constructed earlier for temporary outer bearing support since the valve train exerts a significant downward force on the camshaft. When it came time to install the starter chain drive assembly, the fixture plate had to be carefully removed to avoid extracting the cam.

With the starting system in place, the gearbox cover could be installed. With the cover engaged on the gearbox dowels, a piece of 3/32" steel welding rod inserted horizontally behind the cover was used to push the outer end of the camshaft upward so the cover could be slid into place. To remove the cover, a thin spatula can be used to prevent the camshaft from being pulled out of place. If this happens, the lifters, the pushrods, and their covers will have to be removed in order to re-install the cam. I practiced this maneuver with a paint scraper to make sure it was feasible.

With the gearbox cover bolted in place, a test could finally be made of the fully loaded starter inside the engine. Spark plugs were temporarily installed and the flywheel manually turned over a few times. Plenty of compression was evident - much more than in my Howell V-twin. Neither of my shop-made model engine compression gages can fit inside the plug recess in these heads, and so I couldn't make an actual compression measurement. The good news was that the starter had no difficulty in cranking the engine. The starter motor that's currently in the engine is the 165 rpm gear motor (post #148) which spins the engine at 200 rpm.

The distributor was then installed and the timing set to about 15 degrees BTDC using the timing light feature that I designed into the ignition circuitry (post #167). Looking down on top of the distributor, the rotor spins clockwise which is opposite to the direction of the distributor in the original drawings.

Before installing the carburetor, I added 30 ml of oil to the sump and then spent the next few days chasing oil leaks. The first one, which I should have anticipated, occurred between the bottoms of the valve boxes and the heads. This issue concerned only the two outside valve boxes since they're mounted at steep angles. The oil that collects inside them can't drain quickly enough through the tubes intended to return the oil to the crankcase, and so some oil seeps out between the bottom of the valve box and the top of the head.

The leak was easily solved without disassembling everything that had just been assembled. After dropper'ing acetone into the spaces between the valve boxes and heads to flush out all traces of oil, I dropper'd in a small quantity of Loctite 290. This product is a wicking thread-locker that will easily and permanently seal gaps up to .005" after an overnight cure. I should have removed the drain tubes before applying it because I managed to also seal one of them up and eventually had to fabricate a replacement. - Terry


----------



## gbritnell

Terry,
I really enjoy following your builds. The in-depth explanations teach me something every time I red them.
Here's some food for thought. When I built my V-twin I used 90 degrees for the cylinder angle. (Better balance?) l used aluminum for my intake runner with just .015 gaskets at the head joint. The engine started and ran fine for just a short time then it needed the carb richened, more and more until it would finally stall. At that point it wouldn't restart. Upon letting ir cool the same scenario would play out again. As I was running the engine my friend noticed the fuel in the clear supply line was oscillating, back and forth. This was due to the heat migrating from the head, up the manifold and into the carb. This would boil the gas (vapor lock) and if the needle valve was opened it would draw extra fuel to cool it for a short while until eventually stalling. I removed the manifold and machined the head joint enough to insert a Corian spacer. This insulator solved the problem. 
With your cylinder angle at 45degrees I'm thinking you're going to transmit the heat much quicker so when you run the engine be aware of the manifold temperature. 
gbritnell


----------



## mayhugh1

George,
Thanks for the nice comments and advice. Although it's actually in the above photos, it's not at all obvious, and I should have made mention of it in the above text. The square flange on the end of the intake manifold is a pressed-in 1/8" thick Delrin spacer to block heat from the manifold to the carb just as you say. The black-looking flange end that's visible in two of the above photos is the Delrin and not just typical bad photo glare. - Terry


----------



## Rozlo

mayhugh1 said:


> While machining the pistons last August (post #108), I made two sets: a high and a low compression pair. I've decided to use the low compression pistons since they'll present less of a load to the starter motor. Although it wasn't necessary, I machined 'eyebrows' into them for a bit more valve clearance. Even at their mild 5.3 compression ratio, the edges of the engine's huge valves come uncomfortably close to the hemi-topped pistons. After installing rings on them it was time to begin final assembly.
> 
> While re-installing the cylinders, I decided to replace the small pattern 10-32 nuts that I had been using to mount the cylinders to the crankcase and the heads to the cylinders. It was a nit-pick, but the nuts I was using never looked at home on the engine. I spent a day machining a couple sets of flange nuts that are not only more appropriate but provide a few more threads. After bead-blasting, they were painted black with baked-on Gun Kote so they'd blend in with the blued cylinders.
> 
> Another last minute but much more significant change was to replace the bolts in the rocker boxes with studs. In the original design, these bolts not only secure the covers to the rocker boxes, but they're also the shafts for the rocker assemblies. I finally realized that because the heads of the bolts are on the outsides of the rocker box covers, a lot of disassembly was going to be required to merely verify the rocker boxes are properly receiving and draining oil. All four of the 4-part rocker arm assemblies were going to have to be pulled in order to remove the covers, and this means the pushrod assemblies would have to be removed as well.
> 
> Both ends of the studs were drilled/tapped for 5-40 setscrews that were installed with permanent thread-locker to provide wrench-able hex sockets. The studs not only allow the covers to be removed without disturbing the rocker assemblies, but they also simplify installation of the pushrods and covers.
> 
> I wanted to duplicate the signature acorn nuts I've seen on the rocker boxes of the full-size engines. I was about to machine my own when I located some already polished stainless acorns of the correct size in my collection of scrap fasteners. The only problem with them was that they were threaded 1/4-20 instead of 10-32. Since there was no room for a threaded adapter, I bored the nuts out for plugs that were pressed, Loctite'd, and pinned into place. After threading the plugs, I made a set of teflon gaskets to seal them to the covers.
> 
> Another loose end involved sealing the four valve box covers. These covers have extremely narrow mounting flanges with lots of mounting holes and aren't well suited to a conventional gasket. I didn't want to use a messy sealer, so instead I used this vinyl sheeting that I found in a local craft store:
> 
> https://www.amazon.com/Oracal-Glossy-Permanent-Vinyl-Inch/dp/B01N42YR3P/ref=sr_1_6?crid=2HA1C5QA6S92E&keywords=oracal+651+vinyl&qid=1558133549&s=gateway&sprefix=oracal+651+vinyl,aps,183&sr=8-6
> 
> It's 2.5 mils thick, adhesive-backed, and intended for making rub-on stencils. Its adhesive probably won't stand up to fuel or to significant heat. But, in this particular application as a gasket completely sandwiched between two machined surfaces, it should be satisfactory. After cleaning the covers with alcohol, they were set down onto the adhesive side of the sheet so the material could be trimmed from around their peripheries using an Xacto knife. Working from the non-adhesive side, the holes were cut remarkably clean using a chucking reamer held in a pin vise.
> 
> The gearbox assembly began with the installation of the oil pump and camshaft. The pushrod/cover assemblies were then installed and the valve lash set. I used the doweled plexiglass fixture plate constructed earlier for temporary outer bearing support since the valve train exerts a significant downward force on the camshaft. When it came time to install the starter chain drive assembly, the fixture plate had to be carefully removed to avoid extracting the cam.
> 
> With the starting system in place, the gearbox cover could be installed. With the cover engaged on the gearbox dowels, a piece of 3/32" steel welding rod inserted horizontally behind the cover was used to push the outer end of the camshaft upward so the cover could be slid into place. To remove the cover, a thin spatula can be used to prevent the camshaft from being pulled out of place. If this happens, the lifters, the pushrods, and their covers will have to be removed in order to re-install the cam. I practiced this maneuver with a paint scraper to make sure it was feasible.
> 
> With the gearbox cover bolted in place, a test could finally be made of the fully loaded starter inside the engine. Spark plugs were temporarily installed and the flywheel manually turned over a few times. Plenty of compression was evident - much more than in my Howell V-twin. Neither of my shop-made model engine compression gages can fit inside the plug recess in these heads, and so I couldn't make an actual compression measurement. The good news was that the starter had no difficulty in cranking the engine. The starter motor that's currently in the engine is the 165 rpm gear motor (post #148) which spins the engine at 200 rpm.
> 
> The distributor was then installed and the timing set to about 15 degrees BTDC using the timing light feature that I designed into the ignition circuitry (post #167). Looking down on top of the distributor, the rotor spins clockwise which is opposite to the direction of the distributor in the original drawings.
> 
> Before installing the carburetor, I added 30 ml of oil to the sump and then spent the next few days chasing oil leaks. The first one, which I should have anticipated, occurred between the bottoms of the valve boxes and the heads. This issue concerned only the two outside valve boxes since they're mounted at steep angles. The oil that collects inside them can't drain quickly enough through the tubes intended to return the oil to the crankcase, and so some oil seeps out between the bottom of the valve box and the top of the head.
> 
> The leak was easily solved without disassembling everything that had just been assembled. After dropper'ing acetone into the spaces between the valve boxes and heads to flush out all traces of oil, I dropper'd in a small quantity of Loctite 290. This product is a wicking thread-locker that will easily and permanently seal gaps up to .005" after an overnight cure. I should have removed the drain tubes before applying it because I managed to also seal one of them up and eventually had to fabricate a replacement. - Terry
> 
> 
> 
> View attachment 109394
> View attachment 109395
> View attachment 109396
> View attachment 109397
> View attachment 109398
> View attachment 109399
> View attachment 109400
> View attachment 109401
> View attachment 109402
> View attachment 109403





You have done an awesome job on this so far, a work of art.


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## mayhugh1

While chasing oil leaks, I got some up close experience with the performance of the Knucklehead's oiling system and then realized I had a major issue. The gear pump, for what little is required of it, is over capacity by an order of magnitude. I eventually came to realize that cranking the engine with the starter will likely flood the top end of the engine with nearly all the oil in the sump before it has a chance to start.

Some calculations that I should have performed earlier show the pump's capacity at, say, 50% efficiency is about .032 cubic inches per pump revolution. This was easily determined by computing the volume of all the little gear pockets that move oil around the inside of the pump housing during one revolution of its driven gear. Since the pump is driven at 2/3 the speed of the crankshaft, the flow rate will be about 4.2 c.i./min. at a 200 rpm cranking speed and about 21 c.i./min at 1000 rpm.

An reasonable sump capacity for this engine is about 60 ml or 3.7 c.i. This level insures the pump's intake is covered and that the crankshaft's flywheels are in enough oil to whip up windage to lubricate the engine's bottom end. Calculations, however, show the sump will be entirely drained after only 50 seconds of starter cranking. 

I made a few measurements to back up the calculations. Using a syringe, I calibrated the engine's dipstick to the amount of 5W20 in the sump. A 15 second cranking test dropped the amount of oil in the sump by 20ml or 1.2 c.i. corresponding to an effective flow rate of 4.8 c.i./min.

Unfortunately, easy fixes don't seem to abound. The return rate for the top end oil is on the order of 1 c.i./min and is too low to be of much help during what will likely be a typical run. The intake probably can't be safely restricted to be of much help since the pump will just react by sucking harder. Since the pump is self-priming, a common solution in dry sump model engines is to starve the pump with a slipping two phase mixture using a drip feed input from the storage tank. This won't work for this engine since its crankshaft uses a sump.

The only potential solution that I've been able to come up with is a relief valve on the output side of the pump to drop its head pressure. This is messy because it will have to be located inside the gear box and some heroic tubing work will be required to fit it place. Fine tuning the setting will have to be done by trial and error, which means it will have to be accessible from outside the engine.

If anyone has any other suggestions, I'd be happy to consider them. - Terry


----------



## Ghosty

Terry, can you fit a regulator valve in the case pipe, a simple "T" with a needle valve would work to re-direct a % of the oil flow straight into the sump


----------



## stragenmitsuko

A  relief valve at the discharge of the pump to limit and stabilise the oil pressure . Thinking of a T-kind of piece at the discharge end of the pump , with a small ball and a spring . Pressure can be adjusted on the bench before assembly .
Combine this with a restriction , like a needle valve , somewhere in the feed tube . Possably where it exits the crank case . A small grub screw could be used to adjust it . Or a calibrated orifice in the union would work to .

Feed is directly proportional to rpm , you could slow down the pump rpm by extra gearing .
Hard to do and the problem will still exist at higher rpm .

Reduce the pump's efficiency by altering the bore around the gears or make the gears a bit smaller . 
This could cause problems with priming if overdone and it's a "bad engineering" solution .


I'm sure you'll figure out a way ... 

pat


----------



## minh-thanh

Hi mayhugh1!
just an idea :


The pump will pump both air and oil -> reduce the amount of oil pumped up
It does not change any part of the engine, just add a small tube inside the oil pipe for air


----------



## RonC9876

Terry: Wasn’t the Knucklehead a dry sump engine? I know the Panhead was and mine has an external oil tank with a dual pumping system. The crankcases on these engines can’t hold enough oil in the sump due to the flywheels taking up so much space. I seem to remember reading somewhere that the Knucklehead was the first Harley to use an external oil tank and to actually filter the oil for reuse.


----------



## mayhugh1

Ron,
You're right. The Knuckleheads were dry sump engines. In fact, I think they were the first Harley-Davidson engines to even have a recirculating oil system. Earlier engines were total loss systems using oil that the rider had to add before every ride. The model I'm working on was designed to use a wet sump, though. - Terry


----------



## RonC9876

The air bleed idea sounds plausible. It would be easy to implement and would work like a scavenge pump, pulling in a quantity of air along with the oil. Might not be reliable to prime every time though. The one on my Offy works flawlessly but the one on my Novi needs to be primed manually before a run. Easy to do since the pump is external. Has to do with the distance of lift required. Then again, it might be fine as is. It always amazes me how little oil is actually needed in these model engines. Once the internals are wet with oil, the engine will run happily for some time until the oil gets back to the sump. Not the best situation but this is a model and not required to do any work. Beautiful work by the way. Not that you needed me to tell you that. You already knew!


----------



## Rustkolector

Why couldn't a flow limiting orifice in the line or lines to the heads be used to control excess oil flow to the top end? 
Jeff


----------



## mayhugh1

Rustkolector said:


> Why couldn't a flow limiting orifice in the line or lines to the heads be used to control excess oil flow to the top end?
> Jeff



Jeff,
An additional short restriction in the output would just result in the velocity of the oil increasing during the time its flowing through the restriction. The restriction would have to be small enough or long enough to force pump to max out at its maximum possible pressure before the flow would be limited. I'm already restricting the output with 14 inches of 1/16" i.d. copper tubing, the pump pressure during 200 rpm cranking is at 80 psi, and I don't know how much higher this pump is capable of going. I'm probably dangerously close to breaking something (or maybe damaging the crankshaft) especially if they engine were started at this point. The solution has to involve a pressure relief valve. It's bad engineering to not include one in a constant displacement pump that has a submerged inlet. If I weren't worried long term about the pressure, I'd just raise the height of the pump's inlet and allow it to pump a limited amount of oil to the top end at its maximum flow rate during cranking and then let the pump starve after the engine starts. This would be a quick fix, but it would require keeping a specific level of oil in the engine and not quite how I'd prefer to handle it. - Terry


----------



## Rustkolector

Terry,
Sorry, I forgot you don’t need any oil pressure to the bottom end. Okay, so you add a low pressure by-pass valve directly to the pump discharge. Use a generous sized relief port discharging straight down and the pressure adjustment screw access facing horizontal toward the pump case cover. Once set the pressure should not require change. To keep from putting  a hole in that beautiful pump cover, you can set the bypass pressure by trial and error using a temporary see thru plexi-glass pump cover panel with plugged adjustment access hole. I have used such covers to good advantage to make rod dipper size and oil viscosity selection for very slow speed splash lubricated engines.

BTW…absolutely beautiful work.

Jeff


----------



## scottyk

I did this on my car wash once, just drilled small holes,  progressively larger, and more in quantity in the pressure side of a pump housing until I got the pressure I wanted.  No regulator, no plumbing and it was mounted in it's own reservoir just like this.  I've also seen shock absorbers for cars with internal bypasses in them which is basically a groove machined into the bore, something similar to reduce the efficiency of your pump, might be a bit more elegant than drilling holes.  But as you know these aren't PRESSURE regulators just simple bypass ports which will affect flow rate at all rpm


----------



## mayhugh1

The most significant oil leak(s) turned out to be between the rocker boxes and the valve boxes. O-rings were used between them, but I evidently didn't have them under enough compression to handle the top end flooding that's been going on. Thin (.010") teflon back-up washers reduced the leaks to minor seeps that will likely disappear after an over zealous oil pump is tamed.

With all four valve box covers installed and the leaks apparently solved for now, I was able to perform a slightly longer (30 sec) cranking test. The results were essentially the same as before: approximately 5 cu in/min flow to the top end and 1 cu in/min return to the sump. In 30 seconds the pump moved a whopping 2 cu in of oil into the top end.

If a restriction is added to the output of a constant displacement pump, it will respond by increasing its head pressure. Depending upon how well (or poorly) the pump was machined, it's capable of absorbing significant power from a small engine. My experience with these little pumps is that they can easily generate over 100 psi. I tried to measure the Knucklehead's cranking pressure, but my 60 psi gauge was immediately pegged.

The pressure required to produce a particular flow rate through a tube can be calculated using Poiseuille's Law:

Q = (pi * P * r^4)/(8 * n * L),

where Q is the flow rate, P is the pressure across the tube, r is its inside radius, L is its length, and n is the fluid's viscosity.

Rearranging the equation to solve for the pressure needed to pump 5 cu in/min through the Knucklehead's 14 inches of 1/16" i.d. tubing and assuming 200 centipoise (sorry!) for the viscosity of 5W20 oil, a little math (and some gymnastics with conversion units) produces a cranking pressure of about 80 psi.

The power taken from the engine by the pump during cranking can be calculated by multiplying the pressure times the flow rate (just as with electrical current). At 50% pump efficiency, the result is 1.5W which is responsible for about .15 amps of the starter motor's current. Once the engine starts and begins idling at say 1000 rpm, the power will attempt to reach 7.5W although slip or even stall will likely occur first.

With such a low oil return rate to work with, it would have been difficult to solve the entire problem using a single pressure relief valve. The solution I eventually arrived at was to reduce the pump's head pressure to 15 psi with a relief valve and to raise the height of the pump's inlet. Reducing the head pressure reduces the load on the crankshaft to a negligible amount, and raising the pump's inlet creates a protected sump for the engine's bottom end.

With these changes, the pump will still operate well ahead of the return rate while running, but flow to the top end will be cut off as soon as the oil level falls below the pump's inlet. The top end, which doesn't require much oil, will continue to be lubricated by the small amount that the pump will maintain there. Priming/re-priming isn't an issue for an internal oil pump.

A pressure relief valve is a simple device intended to sit across the pump's output. This particular one is just a piece of brass hex stock bored for a spring-loaded ball and a return-to-sump path. Shoehorning it into the space available inside the engine was more of a challenge because of the precise tubing work required around it.

For a given ball size, the valve's minimum working pressure is limited by its relief spring. A 3/16" ball was as large as I could comfortably work with in the space available. The ball's cross-sectional area transforms the oil pressure into a force that the spring must balance at the valve's tipping point. The spring that produced the 15 psi tipping point was already uncomfortably light, and I didn't feel I could reliably go any lower.

In order to avoid some difficult tubing work, construction of the valve began by creating a soldering fixture using as a template the pump assembled to its already fabricated head pipe. After bolting the assembly to the fixture, the pipe was cut in half using a Dremel abrasive wheel so the valve could be soft-soldered between the halves. A notch was also required for clearance around the dipstick.

In order to avoid defacing the gear box for the valve's one-time adjustment, the spring tension was preset in a bench set-up using a pressure gauge and a 50ml syringe as a pressure source. The set point established by the spring appeared to be very consistent, and the same pressure was obtained using either air or oil in the syringe. For good measure, a weep hole was also drilled through the center of the adjusting screw.

The height of the pump's inlet was raised by cutting off enough of the existing pickup tube to guarantee a 40 ml (2.5 cu in) sump. Filling the gear box to the existing mark scribed on the dipstick adds an additional 10 ml (.6 cu in) which is available to the top end.

With 50 ml of oil in the gear box, a portion of the pump's external drive gear starts out under oil and initially splash lubricates the contents of the gear box. With the cranking flow rate reduced roughly to the return rate, the oil level now changes much less during cranking. Tests showed the level dropping by only 10 ml during a 1 minute cranking test and returning to normal less than a minute later. With so little oil being pumped to the top end, the return measurement is now more sensitive to oil dripping off parts inside the gear box.

During running, the pressure regulator is visible through the dipstick hole and its return-to-sump could be seen working as expected during the cranking tests. Even though the spark plugs were removed for these tests, it was apparent from its sound that the starter is now operating under less load.

The very apparent crankcase pressure pulses that I can feel coming from the dipstick hole have me wondering if the ventilation added earlier to the dipstick is going to be sufficient. The top end oil returns, although high in number, are gravity fed and only 1/16" in diameter, and they won't function as intended if the crankcase is pressurized. Fortunately, though, with the changes just made they won't be as important during running as they once were. - Terry


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## Scott_M

Outstanding !  A very elegant solution.

It won't be long now 


Scott


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## stragenmitsuko

As an illustration of what a gear pump is capable of .
I once made a mistake installing an oil temp sensor  on an 136Hp audi 5 cilinder engine .
That sensor replaces the bolt that holds the pressure regulator spring in place .
Part of the regulator was assembled backwards , basicly disabling  it  .
Stupid I know , but helas mistakes do happen .

So I started the car and it would idle for a few seconds and die .
Then the starter would hardly crank the engine . Tried  that several times , hadn't a clue what
was happening .  So finally I hit the gas , and BAM suddenly the oil filter exploded .

Later on , with the return valve put in the right way , I found out that most of the white metal
on the crank and rod bearings was simply gone and oil pressure now dropped below alarm level at idle .

A costly mistake it was .

Pat


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## dethrow55

outstanding job. been watching this build from day one, been learning a lot ...great work


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## mayhugh1

With the oil leaks and the pump problem hopefully behind me, it took only a couple satisfying hours to complete the rest of engine's assembly. Everything went together nicely, but I decided to leave the air cleaner cover off until after gaining some experience with the carburetor. For the first test run, the idle and high speed carb screws were both opened one full turn, and the timing was set to 13 deg BTDC. The spark plugs had been installed only briefly for the initial starter tests, and all the oil system tests had been performed without them. After re-installing the plugs, the engine didn't seem to have as much compression as I had remembered. The head fasteners were re-checked but they were still tight.

Continuing on, I filled the tank with gasoline, switched on the fuel pump and ignition, and then pressed the starter switch. Although the starter had no trouble spinning the engine at 200 rpm, I didn't get so much as a single pop. After verifying the ignition was actually generating sparks, I reluctantly concluded the cranking speed wasn't high enough. Using an extended socket in a battery-powered drill, the engine was spun at some 600 rpm using the contingency hex machined into the flywheel's hub.

After several seconds of cranking, the engine started right up and continued to run on its own. It was pretty loud and sounded healthy, and there was little if any exhaust smoke. I thought I'd just run the contents of the tank through it without attempting any adjustments and then retire for the evening. After 20 or 30 seconds, though, I began noticing exhaust leaking from between the rear cylinder and its head, so I shut the engine down.

While turning the flywheel over manually, it was obvious that the engine now had essentially no compression. My suspicion was that both head gaskets had somehow managed to fail even though the head fasteners were still tight. It was late, I was tired and not thinking clearly, and I should have called it an evening. However, I wanted to make a final measurement of the starter so I'd have something to sleep on. In the process, I managed to reverse the battery leads to the control panel at the rear of the engine. This dumb mistake immediately destroyed the DC/DC converters used to power both the ignition module and fuel pump. The damage to the pump's converter wasn't obvious, but a power device on the converter board for the ignition module had actually exploded.

I knew it was going to be hopeless trying to sleep if I just walked away from the mess I had just created, and so I worked until sunrise inside that over-filled control box that I hoped I'd never have to revisit. I had replacements for the modules, and after installing them I added diodes to protect them from me in the future. After thoroughly testing the repairs, I spent most of the next day sleeping but only after kicking myself a few more times for not installing those diodes in the first place.

Upon removing the heads, I found two failed teflon head gaskets as expected. Both of them had signs of erosion adjacent to the exhaust valves which are in the hottest portions of the combustion chambers. Curiously, both sides of both gaskets were covered with oil which was unexpected since the run had been smoke free. While I had the heads off, I also vacuum checked the valves and saw no measurable leakage during several 30 second tests.

My suspicion is that the gaskets had been coated with oil long before the run. With all the top end flooding that went on during the oil system tests, oil had likely made its way past the valve guides and into the combustion chambers.

My current theory is that instead of both head gaskets suddenly failing at the same time, neither of them had actually been properly compressed during assembly. As shown in one of the photos, each head has a .015" deep recess that accepts an identical diameter boss machined into the top of the cylinder. I reserved a portion of this recess for registering the heads to insure proper and consistent mounting flanges for the intake manifold that's attached to them. The manifold's built-up construction has a number of soldered joints that are best left unstressed by consistently mounted heads. The original plans recommend using .015" thick copper head gaskets which would have completely filled these recesses. I didn't use copper because the shallow head fasteners aren't capable of creating the force needed to compress even annealed copper. Instead, I made a set of gaskets from .010" thick PTFE sheet so I could reserve .005" of the recess for registration purposes.

It's possible that with so little depth, the heads really didn't end up entirely within their recesses. It's also possible that the cutter used to machine the recesses left enough corner radius that the close-fitting heads bottomed on them before compressing the gaskets. In any event, if the gaskets had been compressed it doesn't seem reasonable that so much oil would have been found on them. The engine's compression at the time of the first run was likely so low that the starter's cranking speed wasn't sufficient to generate enough manifold vacuum to draw fuel through the carb. This lack of fuel would explain the lack of even a single pop while cranking the engine with the internal starter.

Some .020" PTFE sheet for a new set of teflon gaskets should arrive by mid-week. While waiting, I'm designing a set of dies that will allow me to emboss a sealing ring in a thin sheet of copper. I came across this interesting idea for a copper head gasket in a post made by George Britnell several years ago (post 720):

https://www.homemodelenginemachinis...el-hit-and-miss-i-c.10091/page-36#post-124258

I don't know if this has actually yet been tried out on a model engine, but if the heavier teflon doesn't work out, it may become my third attempt. - Terry


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## michelko

Hi Terry
These are some bad News, but heads up i am sure you will work this out.
Have you thought About using some gascet stuff like elring ewp 210 for example. 
It can be purchased in different thikness like 0,3- 0,5-1,0mm
it holds up to 100 bar and 400°C. I used it on my Bugatti build with some good results.

Michael


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## tornitore45

You are not the first to connect a battery backward.   I bought a replacement LED position lights for my trailer and the silkscreen on the PCB was wrong polarity, but I caught this blunder before powering.

There are to way to protect. A series diode like you used, but for higher currents applications the diode loss or the V drop is not acceptable. In that case a backward diode across the input preceded by a fuse will blow in case of battery reversal.


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## gbritnell

Hi Terry,
Over the course of many years I have tried all different types of materials for head gaskets. For my hit and miss engines I settled on Teflon and due to the nature of these engines have had good luck with this material.
For my higher compression multi-cylinder engines I tried Teflon, Copper and other assorted materials. From my full sized engine experience I made copper gaskets with a raised ring created with a die. When the head was tightened it would compress the raised ring and create the seal. This type of gasket worked for non water cooled engines but for my engines with liquid cooling the copper wouldn't seal everything properly, even with the slightest silicone ring around the water openings.
 When I worked as a Patternmaker our shop used a lot of different material for gasketing. I had a piece of one of the materials and gave it a try. It worked great. It sealed the compression, held up to the heat and pressure and sealed the water openings. I have used this material for all my water cooled engines since.
The original piece had a name on it and I was able to track down a supplier in Cleveland. When it talked to someone there he said they only sold it in 4'x4' sheets but he would see if he could find some drops to send to me. That didn't pan out.
At that point I went to my go-to supplier, McMaster-Carr and searched through their sheet gasket material and came up with what seemed comparable to the other material that I had. 
It's labeled as: Oil resistant high strength Aramid/Buna-N gasket material.  The product number is 9402K21
It has worked great on my engines. My 302 has at least 30 hours of running with the same gaskets. I have used it for my flathead and so far I have about 2 hours of running with no problems. 
I'll send you a PM to my direct email in case you have any other questions. 
gbritnell


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## gbritnell

Terry,
I can't find a way to send you a PM so contact me at: [email protected]
gbritnell


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## mayhugh1

While waiting for the .020" teflon sheet to arrive, I performed a few rough calculations to better understand what to expect from teflon as a head gasket since I had no previous experience with it. The reason for its popularity as gasket material has to do with its ability to deform under pressure and fill imperfections in the mating surfaces to be sealed. Up to a certain point, teflon will compress elastically which means it will return to its original thickness when the pressure is removed. At higher pressures it will deform plastically which means it won't return to its original condition. Teflon has another and annoying property, however. Under pressure and over time, it will creep or cold flow and continue to plastically deform a tiny (for us) amount.

In order to estimate the magnitudes of these deformations, the applied pressure is needed. Each aluminum head has five 8-32 fasteners whose maximum recommended torque in aluminum is 10 inch-lbs. If I assume that I'll be able to torque them to 5 inch-lbs using my calibrated wrist, I can expect about 175 lbs of clamping force from each of them. With five fasteners and a 2 square inch gasket, the applied pressure will be close to 450 psi.

Using 50 kpsi for the modulus of elasticity of virgin PTFE predicts almost two tenths deformation for a .020" thick gasket under such clamping pressure. I've included a graph of the stress/strain relationships for PTFE at a couple temperatures of interest for a head gasket. The changing slopes reflect the deformations' transitions from elastic to plastic, but the important take away for a head gasket application is the effect of temperature.

Interpolating the 300F strain (a reasonable upper temperature for a model engine's air-cooled head) for a 450 psi stress gives 3% which translates to a .0006" deformation for a .020" gasket. If the heads are allowed to reach 400F, the deformation will increase to over a thousandth. In any event, after the heads have seen such operating temperatures, the fasteners will likely need to be re-torqued some 5-10 degrees.

Since the machined recesses in the heads are .015" deep, I selected .020" for the gasket thickness in order to completely fill the recesses and to keep the heads off the cylinders. I originally tried using .005" of the recess's depth to register the heads for mounting the intake manifold. This created an issue since the cylinders didn't seem to properly settle inside such shallow recesses, and I had leaks while trying to use .010" gaskets. Now, with no recesses for registration, the head fasteners will have to be torqued with the intake manifold in place to insure its proper alignment. It now becomes very unlikely that the cylinders will end up centered over the recesses. So, it becomes important to insure the heads don't end up bottoming on the cylinders due to gasket deformation as this would again cause a loss of gasket seal. The above calculations show this shouldn't be a problem.

Before tearing the engine down (again), I took a final set of photos with it fully assembled. Except for the plug wires that still need to be shortened, there shouldn't be any significant changes to the engine's exterior. - Terry


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## bigearl91

Enjoying the attention to detail on the ancillaries! 



mayhugh1 said:


> Teflon has another and annoying property, however. Under pressure and over time, it will creep or cold flow and continue to plastically deform a tiny (for us) amount.



Just out of curiosity - would this mean that you would need to periodically check the torque of the bolts/studs to make sure they are within spec to avoid any potential burst gaskets down the line?

Ta
Earl


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## mayhugh1

bigearl91 said:


> Just out of curiosity - would this mean that you would need to periodically check the torque of the bolts/studs to make sure they are within spec to avoid any potential burst gaskets down the line?



Earl,
A handbook from a  gasket manufacturer that I read recommends re-torquing a teflon gasket 24 hours after initial installation. Those gaskets, however, sometimes contain a filler and aren't made from pure teflon. In a model engine we aren't applying much pressure as you can see from the stress/strain graph, and so I would think a re-torque after the gasket has seen high heat would be worthwhile. After that, not much is going to change. I'll let you know what my experience is, though. - Terry


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## propclock

I recommend you investigate Gortex. It is an expanded? PTFE It has all the 
advantages of PTFE but the creep is limited. I use it for head gaskets, no failures
so far. I don't know if you can get it that thin though. 
Your engine is beautiful, both inside and out. 
Thank you for documenting your work.


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## mayhugh1

The new sheet of teflon arrived and, after installing the new .020" thick gaskets, the engine's compression returned with a vengeance. Compression is now so high that I can barely grip the flywheel tight enough to rotate it through the engine's compression bumps. After sitting for a day or so, there didn't seem to be any change.

For a first run with the new gaskets, I filled the sump with 50 ml of 5W-20. The internal starter turned the engine over, and this time I got a few pops, but I ultimately had to use the drill starter. The engine started and ran on its own, but there was a huge amount of smoke and oil coming from the exhaust. We're currently having messy wet weather down here in central Texas, and so all my testing is being done inside my shop. I had to shut the engine down after only 10 or 15 secs while the air in the shop was still breathable. Before ending the run, a few throttle blips had no effect on rpm - maybe not surprising since the only carb adjustments so far have been to blindly open the low and high speed needles a single turn. Early indications are that no fuel is being drawn through the high speed jet.

Since an unreasonable amount of smoke accompanied the improvement in compression, I performed a test to see if there was still a top-end flooding issues with oil being sucked past the valve guides. A run with the external feed line disconnected from the top-end and diverted back into the crankcase through the threaded dipstick opening showed no change in the exhaust.

Each two-ring piston has a machined groove containing an array of radially drilled holes located just below its lower ring for oil control. This design is fairly common in multi-cylinder model engines and, although effective, appears to be overwhelmed by the 50 ml sump. I've included two CAD drawings showing 50, 30, 20, and 10 ml oil levels overlaid across the crankshaft components. With a 50 ml sump the counterweights are well into the oil which also kisses the connecting rod at its lowest position in the crankcase.

Another test using 30 ml, a level that's actually below the pump's inlet, placed the rims of the counterweights just under the oil's surface. The smoke was reduced but was still not acceptable. Such a result wasn't expected because I've been underestimating the windage inside the crankcase. Unlike other engines I've had experience with, this one has very little crankcase volume in comparison with the large amount of air being shoved around inside it by the asymmetrical motions of the two pistons. The result is a vigorous storm inside the crankcase with oil laden air being alternately exchanged between the crankcase and gear box through the seven distributed vent holes between them. An unexpected bonus, though, is a nice lubricating mist inside the gear box.

After a few more runs, I had experimentally determined the optimum sump level to be an unexpectedly low 10 ml. Keeping in mind that the crankshaft bearings are ball bearings and the rod bearings are roller bearings, my definition of an optimum oil level is one that creates just a hint of smoke in the exhaust to show the bottom end isn't running dry. To maintain this level, I made a new inlet pick-up tube that I soldered to the pump.

The full-size engines used similar bearings, and their narrow crankcases likely created similar oil control issues. I can now appreciate why, even with the engine's high impact loads, the designers chose roller bearings over sleeve bearings whose lubrication requirements would have created the issues that I ran into.

To verify the new pick-up, I filled the gear box with 20 ml of 5W-20 which provided 10 ml or .6 cubic inches to be pumped to the top-end. (This level may be later increased to 25-30 ml after some of the other issues are worked out.) The exhaust is now well behaved, but issues remain with the starter and carburetor. (For this last run, I opened the carb's high speed needle another 1-1/4 turns but still with no improvement in throttle control.)

So far, the head fasteners have remained tight. Although I'm probably going to tackle the two known remaining problems out of logical order, my nest step will be to take a look at the starter issue. - Terry


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## stragenmitsuko

Quite odd then that it didn't smoke on your first attempt , and now with basicly just a thicker headgasket it does .


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## mayhugh1

stragenmitsuko said:


> Quite odd then that it didn't smoke on your first attempt , and now with basicly just a thicker headgasket it does .



The (huge) increase in compression compared with what I had using the original poorly sealed gaskets must have have affected the pumping action enough inside the crankcase to account for the difference. The compression had fallen so much at the time of that first run that I thought  it was a waste of time to even try starting it. I admit, though, I'm having a hard time making my peace with what happened as well. - Terry


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## Ironmanaz

Don't forget the big ones have dry sump & scrapers!


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## Ironmanaz

Scavenger pump - on my old Chief, the oil tank was by the gas tank. first thing you would  do after kicking it over is pop the oil cap off to make sure the scavenger pump was returning. Otherwise, it would be wet sumping & smoking like hell.   Not so easy on my old Knuck, cause the oil tank is under the seat.


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## johwen

Rustkolector said:


> Why couldn't a flow limiting orifice in the line or lines to the heads be used to control excess oil flow to the top end?
> Jeff


Johwen here... One way i would  adopt to control oil flow would be to as you have put in an pressure relief valve however I would have made it adjustable by using a screw to increase or decrease the the spring pressure. Alternatively a by pass pipe from the pump outlet to the sump with an adjustable outlet via a needle vale to control maximum bypass Cheers John


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## mayhugh1

There may be an issue with the carburetor and/or intake manifold that's creating the need for a much higher starting speed than I had expected. The engine won't start until the drill starter approaches some 1000 rpm. Before revisiting the carburetion, though, I want to raise the speed of the internal starter.

The motor currently inside the Knucklehead is a 165 rpm planetary gear motor from Servo City:

https://www.servocity.com/165-rpm-hd-premium-planetary-gear-motor

My original testing (beginning with post #128):

https://www.homemodelenginemachinist.com/threads/another-knucklehead-build.27584/page-7

was done using the 437 rpm version of this motor using my Howell V-twin as a makeshift load. This motor was capable of spinning the Howell at 400 rpm and was used to come up with a ballpark spec for the Knucklehead's starter. During the design of a chain drive to connect the motor to the engine's crankshaft, I discovered I'd have to live with a 20% step up between the gear motor's output shaft and the engine's crankshaft meaning that the torque delivered to the crankshaft would be down by 20%. I initially installed the 165 rpm version of this motor in the Knucklehead because of its highest available torque along with a potential 200 rpm cranking speed which at the time was my guess at a usable minimum.

The motor current required for a particular torque can be found from the motors' torque/current curves which are sketched in the first photo. The slopes of these curves, provided by the manufacturer, have been adjusted for the chain drive, and so they reflect the 20% torque drop at the crankshaft. The maximum torque available from any of the motors is limited by their 20 amp stall current.

A starter's cranking speed in a V-twin application is difficult to calculate because of its wildly varying load. Between compression strokes, the motor will attempt to run at its no load speed. A V-twin starter will spend roughly 60% of its time effectively unloaded. When loaded by a cylinder in its compression stroke, the rpm will attempt to fall commensurate with the torque it must deliver. However, inertia, which will be dominated by the flywheel's angular momentum, will attempt to smooth out any changes.

The first scope photo contains the 165 rpm gear motor's current waveform generated during the first second immediately after the starter switch was pressed. There was an initial, but brief, inrush current before the motor began spinning and creating a counter emf. The starter ran into its first compression load while the cranking period was still long compared with the cylinders' leak-down times. By the time it encountered the second one, its speed had increased, and the current peaks were beginning to stabilize at some 11 amps corresponding to torque peaks of 320 oz-in.

The engine's irregular power strokes can also be seen in the waveform. It shows the rear cylinder's power stroke occurring some 250 ms after that of the front cylinder. Inside the 560 ms 4-stroke cycle this corresponds to 321/411 degree firing intervals (compared with the 315/405 degree theoretical values). The small discrepancies are likely caused by the system's inertia.

The cranking speed is slow enough to discern the bifurcated loads presented by the two cylinders' closely spaced TDC's. The highest of the two peaks is created by the load presented by the cylinder in its power stroke whose piston is approaching TDC with both valves are closed. Just 45 degrees earlier, the piston in the other cylinder is also approaching TDC but in preparation for its intake stroke. The load created by its piston moving upward with its intake valve closed and its exhaust valve closing is also significant until the intake valve opens near TDC.

The second scope photo contains a snapshot of the same waveform several seconds later when it has had time to stabilize. The 560 ms 4-stroke cycle includes two crankshaft revolutions and corresponds to a 214 rpm cranking speed which, mysteriously, is 10% higher than should be possible.

If the torque curves are examined with these measurements in mind, it's obvious that the engine's 320 oz-in peak torque requirement should be easily satisfied by the 313 rpm version of the gear motor, while potentially doubling the cranking speed. The 437 rpm motor, on the other hand, might provide even more cranking speed, but it will come up about 65 oz-in shy of producing the required torque. Some of this shortfall may be compensated by the flywheel's additional angular momentum provided by the higher cranking speed. Therefore, I decided to replace the 165 rpm gear motor with the 437 rpm version.

The third scope photo contains the 437 rpm motor's current waveform during the first second after the starter button was pressed. The 20 amp inrush current along with a short stabilization period is still visible, but the bifurcated peaks have disappeared. This motor is spinning fast enough for the flywheel's angular momentum to carry it through the relatively small load variations created by the cylinder approaching its intake stroke. In steady state, the current peaks are just kissing their 20 amp maximums thanks to the flywheel covering the torque shortfall.

The fourth photo shows the current waveform after the cranking has had plenty of time to stabilize. The peak currents created by the rear cylinder in its power stroke are barely reaching 20 amps and those created by the front cylinder are a bit less which probably indicates some minor compression difference between the two cylinders. The 320 ms 4-stroke period corresponds to a 375 rpm cranking speed which is 30% lower than its 524 rpm no-load value.

Out of curiosity, I also temporarily installed the 315 rpm motor for testing. The peak currents were 17 amps as expected, but the cranking speed was only 240 rpm which was 40% lower than its 375 no-load value. The lower cranking speed also uncovered a portion of the bifurcated loads.

In the end, I re-installed the 437 rpm motor which seems most optimum of the three I had available to test. Actual engine starting tests using this motor showed the drill starter was still required to cold start the engine. The internal starter, though, was now able to restart the engine after it had been run for a while. The next step will be to revisit the carburetion. - Terry


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## mayhugh1

Most everything on the engine now seems to be in reasonable working order except for the carburetion. The carburetor, a modified version of the one in the original drawings, has an idle port located downstream from its butterfly throttle. Its adjusting needle, located on the side of the carb body, is semi-accessible through the pushrod covers. It was arbitrarily opened one full turn when final testing began and hasn't been touched since.

A 1/4" Venturi, immediately behind the butterfly, receives fuel from the main (high speed) jet. Above idle, the engine's speed should be controlled by the butterfly by regulating the volume of air/fuel allowed into the engine. Fuel is drawn from the main jet and mixed with high speed air flowing through the Venturi and is controlled by a second needle that's accessible from below the carburetor bowl. It was also opened one turn at the beginning of testing and an additional turn sometime later.

Fuel from both the low and high speed circuits is often required to start a cold engine because of the fuel's temporarily low volatility. By restricting the amount of air allowed into the carb using a mechanical choke (this carb has one), or a finger over the carb's inlet, the Venturi increases the velocity of a smaller volume of air flowing through it, and this causes additional fuel to be drawn from the main jet. The resulting overly rich mixture is easier to ignite in a cold engine.

The current symptoms are that an unreasonably high cranking speed is required to start the engine, and once it does start, the throttle has no effect on speed. The engine idles indicating the idle circuitry is functional, but the symptoms are those of a non-functioning high speed circuit.

To begin troubleshooting, the carburetor was removed and a vacuum gage attached to the intake manifold. The gage indicated pulses 10 psi below atmospheric while cranking the engine with the internal starter. Although I don't have any comparative measurements from other engines, these results seemed reasonable for this engine's displacement and manifold volume. Admittedly, the 1/4" Venturi could be smaller, but it shouldn't be a show stopper.

After disassembling the carb and taking a close look at the main jet assembly, it seemed to me that with the needle's current taper, I should more likely be dealing with a rich and overly sensitive high speed jet instead of one that's not working at all.

I eventually sealed the bowl with a plexiglass cover using a bolt running through its center in order to simulate conditions inside the bowl with the pump running. At first, everything appeared normal with the recirculating loop maintaining a full level of fuel in the bowl. However, after adding a bit of dye to the fuel and playing with the pump voltage, I soon discovered a vortex beneath the surface encircling the bolt. This vortex was uncovering fuel from around the bolt's mid-section in the exact area where the inlet for the high speed jet would otherwise be trying to draw fuel. The inside corners of the bowl were actually full of fuel, and it was from one of these that the idle pickup tube had been happily feeding.

Although, with the variable DC converter powering it, I have plenty of control over the constant displacement fuel pump, the vortex was unaffected by speed. I spent a couple days playing with the diameters of the inlet and outlet hoses as well as dozens of screen and baffle designs with no success. I eventually realized my bowl design had a fatal flaw.

All the other fuel loops I've made have been three hose designs with remotely located carb bowls. In those loops, fuel was pumped into the bowl through an inlet located on its bottom. The return to-tank-line was also on the bottom, but an internal standpipe connected to it regulated the fuel level. The carb drew its fuel from a third tube located on the bottom of the bowl where turbulences were relatively minor.

The Knucklehead's carburetor with its integral bowl requires only two hoses. The inlet was installed mid-level in the bowl, but the return-to-tank line exited the bottom of the bowl so unused fuel would drain back into the tank. The bowl's only venting is through the return-to-tank hose which allows some latitude in setting the pump voltage. Excess volume is merely returned to the tank. Testing at the time of completion of the carburetor showed the fuel level inside the bowl was consistently controlled with the pump voltage. However, for those tests, the top of the bowl was left open while its bottom was sealed with a short screw and o-ring. What happened is that when the bowl was sealed to the carb, a vortex was created around the main jet that prevented fuel from entering it. Sealing the bowl to the plexiglass cover allowed the vortex to be seen spinning around the central screw although it was hidden beneath the surface of the fuel.

I hoped to salvage the bowl, so I removed and sealed up the original mid-bowl inlet so I could attach the pump to the existing bottom tube. A new outlet was then machined and installed as high up on the side of the bowl as possible. Testing showed the vortex was finally gone.

Testing on the engine showed I'm finally getting fuel - too much fuel - from the main jet. The internal starter was able to start the engine a couple times, but it's now running way too rich with lots of black smoke. The throttle is now having some effect, but a new main jet assembly is now going to be required. - Terry


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## gbritnell

Hi Terry,
Over the years I have experimented with, modified and built all types of carbs for my engines. Like the one on your engine I have made, or tried to make miniatures of the full sized versions. This would include air bleeds and accelerator pumps. No matter how I experimented I just couldn't get the desired overall running performance that I thought I should. There was a very gifted builder, Lee Root, who created some amazing I.C. engines and on one of them he used a very complex carb, somewhat replicating a Stromberg 97. Strictly I.C. magazine published a build article on it so I made one. Here again it would run my V-8 engine but not like I would have hoped for. There is a group of fellows that belong to the BAEM out in California and for some of their engines they use modified shall we call it, weed eater carbs. The small 2 cycle Walbro type. To use these carbs even in the modified state they require a fuel pump or delivery system. I played around with these, again not garnering the results I wanted. 
I ended up building carbs based on the simple air bleed types found on RC airplanes. For each engine configuration I would build a carb that represented the full sized version but the internals were just basically an air bleed. I must say that I have achieved very good performance with these carbs, not perfect but very good. 
Knowing that a lot of the properties of a running full sized engine don't scale well, air flow, centrifugal force etc. I have always wondered how the vacuum signals react when making ultra tiny porting in highly complex model carbs. 
The one thing I have discovered over the years is that small is better when it comes to venturi size. My engines all have bores in the .875 to 1.25 range and my largest venturi size is about .210. 
I wish I could help you but when it comes to small carbs it just takes a lot of experimentation.
Best of luck,
gbritnell


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## petertha

Would it help if kind of snorkel tube fitting was made to attach over the center post inlet hole? An extended tubing could be bent/orientated such that the opening ideally occurs in more consistent, stable flow area elsewhere in the bowl. That could be laterally over or also up/down from where the main inlet is. Something add-on temporary just to see if it improves things without a major redesign?

I'm assuming the inlet/outlet positions are the prime contributors to the flow path. Maybe another option is install a temporary diverting plate or perforated plate or screen.... something that causes a bit of natural turbulence & dissipates the main toilet bowl vortex without creating stagnation issues in another areas. Its hard for me to visualize the center being so starved though even if there is an obvious  predominant flow around it. Its a relatively small compartment, low velocity, liquid filled...but what do I know. 

I've seen some peculiarities of fuel flow into RC engines carbs/venturi's though. George is right, weird things happen at reduced scale. Sometimes the components look so simple & borderline crude. But just try tweaking a slit to a hole or moving the orifice to a slightly different spot. You can turn a good runner into a dog so easily. Makes you wonder if model carbs were trial & error until something worked or some very smart people with a lot of determination. But that's more air/fuel 2 phase mixing conditions. A different headache


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## mayhugh1

With the bowl attached to the carb body, I used the fuel pump to pressurize it while watching the main fuel port inside the Venturi. I suspected I already knew the answer, but I wanted to confirm that the overly rich mixture seen during my last engine run was due to lack of control by the main jet needle. What I also saw, though, was fuel flowing up around the outside of the main jet.

In the Knucklehead's carburetor, the main jet is also used as a fastener to secure the bowl to the carb body. In the original design, this fastener was expected to provide the clamping force to simultaneous close three seals. These are: 1) a compressed o-ring between the underside of its washer'd head and the bottom of the bowl, 2) a teflon gasket between the top of the bowl and the underside of the carb body, and 3) a metal-to-metal seal between the end of the jet and a mating surface inside the Venturi. I was concerned about trying to make all three happen simultaneously, and so I modified the design to eliminate the metal-to-metal seal, and I allowed the jet to protrude through the Venturi. This was evidently the source of the leak I was seeing.

The o.d. of the jet's tubular body is .124", and the i.d. of the bore containing it is .126". At the time, I assumed the fit would be close enough, but after calculating the area of the gap between the two, I discovered the effective flow area of the gap is about half that of the main jet itself. It's very likely that much of the exhaust soot seen during the last run was created by fuel being drawn through this leak.

I couldn't retain the two-seal solution without an extensive redesign of the entire carb, and so I decided to return to the three-seal scheme in the original drawing. The Venturi is a separately machined part that was Loctite'd inside the carb body, and so accommodating the third seal required removing it and starting over with a new one. In order to prevent over stressing its epoxied construction, the carb body was carefully supported while the Venturi was machined away using a boring bar.

The hole in the new Venturi for the end of the jet was drilled using a .125" ball end mill, and the tip of the main jet was machined to match. (The diameter of the fuel passages through both the jet and Venturi is .046".) Since I was making a new Venturi anyway, I also reduced its i.d. from .250" to .212" based on one of George's comments above. Machining the length of the main jet to accomplish all three simultaneous seals took a lot of care, and I really won't know if I was successful until some leak-free time has been accumulated on a running engine.

Although I'll likely regret making two changes at the same time, I also made a new high speed needle starting again with a .056" diameter darning needle. After chucking it in the lathe, I ground an eye-balled taper on one end that appeared to be capable of gently closing up the .046" main jet passage. It was then Loctite'd into its adjusting screw.

Although in the right direction, the two carburetor changes made only a modest improvement. The black exhaust smoke and overly-rich condition was gone, but the engine will only start and idle as before. The throttle still no effect on engine speed. This one's going to be a toughie. It's time to step back and figure out why the main jet seems to have less effect than the leak around it. - Terry


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## mayhugh1

R.I.P.

I was trying out a new main jet needle this evening when something went awry inside the gear box. My guess is that one of the pins securing the main drive gear to the crankshaft slipped out and set off a chain of events that not only chewed up several gears but may also have bent the crankshaft. I'm not sure how any of the pins holding the gears in place could have moved as they were very snugly fit. The gears can be replaced but the crankshaft may be a different story. I'm going to need to figure out what happened so it doesn't reoccur. - Terry


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## Ghosty

Dam, it was so close to being done.


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## stragenmitsuko

OMG that's terrible .


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## gbritnell

Terry,
I'm extremely sorry for this turn of events. I was waiting for the minute when I could hear this beautiful engine run. I have never had a catastrophic event like this but have experienced similar occurrences.  With all the time and work you have invested I'm sure once you settle down and analyze what took place you'll rebuild the engine. In following your builds I know you have too much dedication to just let things go. 
Take care and keep us informed.
gbritnell


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## kvom

I was going to "like" your post, but that seemed inappropriate.  I'd hate to see this build abandoned though.


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## RonC9876

Terry: This is a terrible thing that has happened. I know that after you get over the shock you will recover and rebuild. I have had similar mishaps on a couple of my engines. I had a gear tooth break off on a high speed run of my Offy and that one tooth wiped out the twelve gears that drive the dual overhead cams. This was due to a poor attempt at case hardening these gears made from mild steel. I also had a crankshaft get bent on my five cylinder radial after it’s maiden run when I covered it with a rag and left it on the bench. Our cat from Hell ,that we had at the time, decided it needed that rag to sleep on and pulled the engine off the bench and onto the concrete floor in my basement. Not only did the crank bend but my favorite laminated prop was shattered as well. With having built some 75 different engines of one kind or the other over the years, I guess some of these things can be expected. But boy it hurts! These creations of ours are near and dear to our hearts. But then you realize that with the experience you have all can be corrected and with less effort than you thought possible. Best of luck and I feel your pain. Ron


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## doc1955

Man that has to be a terrible feeling. Some times you need to take a break step back and take another run at her. I'm sure you'll  sort her out and get back at it.


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## brotherbear

Arguhhhhhhhhhhhhhh!


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## Cogsy

That's terrible news. Like the others, I'm confident you'll overcome this catastrophe and rebuild, but you definitely deserve some time off to recover.


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## mayhugh1

I've got the entire engine disassembled and all the parts in labeled plastic containers. It looks like the real damage is limited to three gears and two bearings - nothing that can't be re-made in much less time than it took to originally make them. During its sudden stop, the two piece crankshaft with its tapered crankpin was tweaked out of alignment as far as its end bearings would allow leaving me with a noticeable wobble at the bearing in gear box cover. Nothing was actually bent, and so fixing it will just be a matter of breaking down the crankshaft assembly and reassembling it inside the alignment fixture used originally.

I thought I'd be more depressed about what happened, but I'm actually looking forward to the next several weeks. All the really tough major machining is completed, and I'm more than happy with it. This will be a second chance to correct some pesky issues with the oil return scheme inside the rocker boxes that have been an ongoing source of irritating leaks. I'm also going to repackage a commercial air-bleed carburetor so I can at least determine if the carb issues I've been having are with the current design or are actually elsewhere. - Terry


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## Ghosty

Good to hear that it was not as bad as first thought. Good to see that it will be finished


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## RonC9876

Terry: Easy peasy. Glad to hear that it wasn’t as bad as first thought. The sight of those shattered parts and wobbly crank would make a grown man want to cry. Onward and upward!


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## ddmckee54

So the engine's not truly dead as a door-nail?  It's just relaxing a little bit while recovering from its' injuries?

Don


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## mayhugh1

It's about to rise out of the ashes ...


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## stragenmitsuko

Like  a fenix


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## ddmckee54

You gonna be running around yelling "It's alive, it's ALIVE", like Gene Wilder in 'Young Frankenstein'?


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## IceFyre13th




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## mayhugh1

The entire engine had to be disassembled in order to get access to the crankshaft. Its construction is very similar to that of a full-size crank, which is a pair of flywheels secured with heat treated nuts on either side of a tapered crankpin. The next step in a full-size rebuild would be to pull out the intelligent hammer and start beating on the crank until it was straight again. In my case, I was able to re-use my original alignment sleeve. In actuality, it wasn't as easy as it sounds because I had Loctite'd both nuts to the tapered pin. This was a big mistake because only one broke free greatly complicating dis-assembly. With nothing to work against, I wasn't able to remove the nut from the other end of the pin leaving me later with a nagging concern about whether I had sufficiently tighten both sides. I didn't want to apply heat to the nearly irreplaceable Stressproof tapered pin since weakening and breaking it would have been a real possibility. In any event, I ended up with the crankshaft's TIR back to nearly zero when measured at the crankcase bearings. The TIR at the very end of the crank's long skinny end was now at .0025" which is a thousandth over the originally measured value. I don't anticipate this being a problem since the crank's noodle'y end could always be finger-deflected this much, and a bearing in the gear box cover will stabilize it. The doweled cam box cover easily slipped into position later, and there's no visible flywheel wobble.

Before I could work up enough incentive to begin re-machining the damaged parts, I really wanted to understand what I did wrong the first time so I didn't blindly repeat the same mistake(s). My conclusions weren't very settling, though.

The 1-1/4" long main drive gear on the crankshaft was originally machined from Stressproof and pinned to the crankshaft using a pair of 3/32" diameter dowel pins. These pins were centered in the roots between the gear teeth and oriented 90 degrees to each other. The holes for these pins were originally drilled and reamed with the gear in place on the crankshaft and both pins were 'snugly' fitted. The rear pin was placed so it would be covered by the starter drive gear and the oil pump gear. The front pin was placed so it would be covered by the camshaft gear. My theory was that even if the pins tended to creep out of position a bit, they would be continually re-centered by the teeth of their cover gears. The rear pin, in fact, had two gears to insure it remained centered.

A half dozen seconds after being drill started, the engine locked up. The crankshaft gear, the starter drive gear, and the oil pump gear were all severely damaged. A third pin in the oil pump gear remained in place and undamaged. The outer crankshaft pin was found undamaged and stuck to the magnetic drain plug in the oil sump along with debris from the gears. The rear crankshaft pin had been sheared. A portion of it was still inside the crankshaft, but the other half was also in the sump.

The two dowel pins were the obvious culprits, but the only sequence of events that I can came up with to explain the damage is pretty difficult to swallow. First, in order to escape damage, the front pin had to have fallen out sometime before the catastrophe. This would have occurred sometime before the engine was started and while the pin happened to be vertically oriented. After the engine was started, the rear pin would have to have shifted in order for its shear line to end up where it was. The incredible thing about this shift is that it had to have occurred while running and within the time it took for the crank to rotate just three quarters of one revolution. Otherwise, it would have just been nudged back into position by either the oil pump gear or the starter drive gear. This single shift would also have had to be great enough to jam up the starter drive gear which was presenting no significant load to the crank. As a result of this jam, the momentum of the flywheel sheared the pin, and its free end continued on to create even more damage. I've not made total peace with this explanation, but it's the best I've been able to come up with. Visualizing those pins, especially the rear one, moving around as required to create the resulting failure isn't easy. In any event, I decided it was time to get on with the repairs.

The first step was to machine a new crankshaft gear. Probably the most critical machining in all the upcoming repair work was to precisely match the dowel holes in the new gear to those already in the crankshaft. I started by using a spindle microscope to measure their locations in the crankshaft. A horizontal rotary was then set up under the mill's spindle to precisely drill and ream the holes through the new gear. After slipping the gear onto the crank and installing a temporary pin in one hole, the other was reamed through for an over-size dowel pin. This pin was then carefully ground down for a tight fit through the gear/crank combination which I augmented with Loctite. With the first pin in place, the process was repeated for the second one. I considered using tapered pins but fitting them in the roots between the gear teeth didn't seem practical, and I wasn't sure a spring pin would handle the torque requirements of the starter motor. In any event, I can't see the new pins going anywhere, although I've been wrong before. - Terry


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## GRAYHIL

Hi All
I am thinking of making this model, it looks challenging but I have studied the drawings and drawn a few of the pieces.
Overall the drawings look top class.
I live in the UK  and so will probably  use the nearest metric fasteners but work to imperial imperial dimensions to produce the parts.

Graham


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## mayhugh1

Grahm,
I look forward to hearing your progress. Another builder in South America also started one by making some castings, but he hasn't reported any progress in several months. Keep us advised and preferably start a build thread.
Terry


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## mayhugh1

Before closing the crankcase up around the crankshaft, I drilled two 3/8" holes through the gear box and into the right crankcase half. With the ventilation previously added to the gearbox, these holes will help equalize the crankcase pressure throughout the engine. I also reworked the pressure regulator to drop the oil pressure to the top end to about half the 10 psi that I had been running. This required sleeving the housing of the existing regulator and re-boring it for a smaller ball and spring.

I had an aha moment as I was about to reinstall the cylinders over the pistons. I realized that I had mistakenly installed the 6.5 c.r. pistons instead of the 5.3 c.r. set that I had intended to use. I should have caught the mixup when I discovered I had to eyebrow them since I had determined much earlier that the lower compression pistons were interference-free. The load created by the higher compression explains why the starter's cranking speed has been lower than what I had originally estimated based upon my Howell V-twin measurements. Since I had plenty of spare rings, I installed a new set on the lower compression pistons before really installing them this time. The rings on the pistons that were in the engine showed no visible wear. There was only about 15 minutes of idling time on them, but the colored oxide left on their o.d.'s during heat treatment was still uniformly visible around all four rings. The .020" thick teflon head gaskets also looked new and were still at their original thickness, and so they were reused.

The brass starter drive gear was severely damaged and had to be replaced. Its shaft was also bent, and the bearings on either end damaged. This shaft is a complicated part that I wasn't looking forward to re-machining. It contains not only an integral sprocket but a difficult to machine face groove that contains the beveled drive gear for the distributor. I generally have poor success with straightening shafts, but with nothing to lose I chucked this one in the lathe for support and went after it with a tiny hammer and wood drift. I was greatly relieved when its .026" runout was reduced to less than a thousandth.

All the gear box bearings are flanged blind press-ins. When I bored their pockets I left a space behind them for a puller. One of the photos shows an example of one of the simple pullers I made to remove two of the three bearings.

Before realizing my piston mistake, I was planning to machine the replacement starter gear from steel since the loading on the starter system had turned out to be greater than expected. The cam gear had received only minor damage, but since it was nearly identical to the starter gear, I decided to machine both replacements from the same brass blank.

For my own learning, I had been running an experiment involving the camshaft/lifter wear. The large valves required fairly stiff springs, and the tiny contact areas between the lifters and cam lobes created concerns about wear. After their oil quenches, the lifters were tempered at 350F and the cam was tempered at 450F. My experiment was to move all the wear to the cam and away from the custom tipped lifters. Here, the contact areas would be allowed to gradually increase as the surfaces wore into each other. My hope was that the wear would eventually diminish as the lobes moved away from yielding leaving minimal damage on the cam.

The lifters showed no wear as expected, but the wear on the cam lobes seemed excessive for the relatively small amount of running time. I decided to switch to my backup plan which was to make everything as hard as the back of Superman's head. When I made the camshafts, I machined two identical copies, and so I re-heat treated the unused spare. This time I used a 3 hour temper at 325F which left it as hard (and as brittle) as I felt comfortable with. Draw tests with a file showed a very obvious increase in hardness compared with the first cam. The spare was then assembled with its newly machined gear and timed to crankshaft.

During disassembly of the engine after the crash, I noticed a significant amount of oil (about 3 ml) laying in the outside corners of both rocker boxes. In the rear rocker box, the nearest pushrod drain hole is the one for the intake valve. This hole is far enough away so the level of oil that accumulates in the corner will continually flood the o-ring seal between the rocker box and the valve box. This has been the source of the mysterious leak that invariably continued well after the engine was shut down. The front rocker box isn't as much of a problem since its nearest drain, the hole for the exhaust pushrod, is closer and the accumulated oil level isn't as high.

With the drain holes where they are, it isn't possible to eliminate the problem by adding something inside the rocker boxes. However, I did find and JB Weld a small machining defect in the rear valve box's o-ring sealing surface that should make a difference. I also redirected the outside corner oil spray nozzles away from the rear surfaces of the rocker boxes and toward their covers to help hasten oil drainage during running.

In addition to straightening two shafts, the final damage tally was four gears and three bearings. After installing the distributor and setting the valve lash, the engine is finally ready to go once more. I can't say the past couple weeks have been any fun, but a number of small improvements made to the engine have definitely made it productive.

I've been studying the jet design in the drawing for the air bleed carburetor that George Britnell posted to the downloads section years ago. I now think the Knucklehead's main jet design is backwards causing it to provide too little control over too much fuel. Since the current carburetor looks like it really belongs on the engine, I'm going to try to re-work its jet assembly before totally abandoning it. - Terry


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## kvom

That took less time than you likely expected.


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## RonC9876

Looking good Terry. Sometimes it isn’t too difficult to straighten a crank. Other times things just get worse as you go along and you have to scrap the part. I have had them go both ways. Not that I make a habit of bending cranks, but things happen. Usually when transporting them to a show and they fall off the cart. You know; trying to cram them on the cart to make the fewest trips to the car as possible. Happened twice in the past. I never learn. Looking forward to some videos of this creation running. Best of luck as always.


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## mayhugh1

With the engine finally back together, I made another attempt at modifying the main jet. The cross-sectional drawings in the first photo show these most recent changes. In the top (original) design, the needle was expected to regulate the amount of fuel entering the jet through the twelve radially-drilled inlet holes at its lower end. In operation, this fuel will be drawn out of its top end by the low pressure area inside the Venturi where it's mixed with the air flowing through the Venturi on its way into the engine.

Based on George Britnell's air bleed carburetor for an engine with similar size pistons:

https://www.homemodelenginemachinist.com/threads/air-bleed-carburetor.29019/

one or two entry holes would have been sufficient. With so many more to deal with, a needle with a pretty challenging taper is required for usable control. So far, I've ground three different needles with essentially no success. The needle that I was testing at the time of the crash was supplemented by a bushing that was pressed over the jet to cover up several of the holes.

For this latest trial, I bushed the i.d. of the jet's output end and lengthened the needle so it has only to meter fuel entering the bushing which now protrudes into the Venturi. The needle's taper is still important but much less demanding. Surprisingly, its performance in the engine was pretty much the same as before. The engine had to be drill-started, and it idled overly rich with neither the throttle nor the needle having any noticeable effect. Something was obviously overshadowing the fuel contributed by the main jet.

For the first time, I began playing with the idle mixture screw and found it too had little to no effect. This was a surprise because the components making up the idle circuit are straightforward, and their machining was easily verified. I removed the carb and plugged the idle pickup tube in order to completely disable the idle circuit. Now, with only the main jet metering fuel, the engine started immediately with the electric starter and for the first time could be made to idle with a clean exhaust. There was still no reaction to the throttle, but control of the air/fuel mixture by the main jet's needle was now obvious, and it functioned as expected. Up until this point, the idle circuit has been supplying an excessive and uncontrolled amount of fuel to the engine that has been masking the contribution from the high speed jet.

With the idle circuit still disabled, I added an atmospheric vent to the carb bowl. So far, the pressure inside the bowl (the pressure that actually 'pushes' fuel into the Venturi) has been defined by the recirculating loop's input/output pressure differential. Adding this vent changed the main jet's operating point, and its needle had to be closed an additional 1-1/2 turns to return to the engine to its peak idling speed. Evidently the pressure inside the bowl had somehow been a bit less than atmospheric. Even though it had no effect on the throttle issue, it's now clear that a bowl vent is required to ensure the carb settings are independent of the pump's speed.

A clue to the throttle issue may lie in the transition space between the Venturi and the intake manifold. This space is different in a model engine application than it is for this style carburetor's more common usage in full-size engines. In this application, the diameter of the intake runner (I need to quit calling it a manifold) is smaller that the diameter of the carb body feeding it. The second photo shows a cross-sectional view of the various areas involved. In a full-size engine the carb feeds a voluminous plenum whose diameter is at least greater than that of the carb's throat. Visually, this space screams for a smooth transition between the carb body and the intake runner. I'm beginning to think, though, that an unfortunate combination of geometries may be reducing the clearance allowed around the butterfly to a difficult-to-achieve level. It would certainly be a disappointment although not totally surprising to discover that the engine has actually been running at its maximum speed all along due to a leaky butterfly. In any event, this is where I plan to focus my attention.

The grandkids are coming in for a week, and since they aren't shop types I'll have some time to think about this. In the meantime, I made a video that captures the project's progress so far, just in case another mishap occurs before the carburetor problems are sorted out:




As an aside, the rebuild has eliminated all the annoying oil leaks. The oil that's blown out through the crankcase vent has increased, probably due to the venting added between the crankcase and gear box. This particular 'leak' isn't of concern since it's typical for vintage engines and almost a requirement for old Harleys. There's probably an oil maelstrom going on inside the engine while it's running that's keeping everything nicely oiled, and that's a good thing. Now, if I can just get it to rev up (or down) ... - Terry


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## RonC9876

Terry: When I first tried adapting a diaphragm carb to my V-8 Challenger engine, I got very little response from the throttle settings. This carb had a 5/8” diameter butterfly valve. I bushed the diameter down to 1/4” to where the butterfly valve diameter was now about the same diameter as the head of the screw holding it to the actuating shaft. The engine would now respond to the throttle settings and main and idle jet settings as well. It was tricky drilling holes in this bushing to line up to the jet holes in the original 5/8” bore. It has worked well ever since. Just my experience with a butterfly valve carb and sizing it to a model engine. Most of my carbs use throttle barrel valves with about the same small bores.


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## mayhugh1

The stock throttle has so little effect on engine speed that it defies logic and creates an interesting problem to solve. Although not a perfect design, a few calculations show that it should certainly be functional. When fully closed, the .005" clearance around the disk is equivalent to a leak of only 5% when compared with the area of the intake runner. The theoretical difference between being fully closed and fully open (100% intake area) is about 35 degrees of rotation. Its effectiveness, however, is getting lost somewhere - either in the transitional space labeled D in the cross-sectional drawing of the induction system or within the long complex intake runner itself.

In the full-scale carburetor applications that I'm familiar with, the carb typically feeds an induction system whose diameter is at least as large as the carb's i.d. below its throttle. In this case, though, the .312" intake diameter is significantly smaller than the .500" i.d. of the carb. For air-only flow, the throttle would probably work as expected, but once fuel is added, the density and momentum of the resulting mixture are changed. It's difficult to appreciate just how much they're changed until you see a typical air/fuel flow inside an actual carburetor. I found a Youtube video demonstration:



of a clear plastic carburetor attached to a small Briggs & Stratton engine. The carburetor in the video is relatively simple and very similar to the Knucklehead's, but its throat matches the engine's intake. A two minute segment beginning at 1:20 is pretty eye-opening and shows a much wetter mixture than I had been picturing. I had been visualizing the flow through the carburetor as something from a air hose when I should have been thinking more in terms of a garden hose. This made me suspicious of the stepped down area looking into the intake, and had me wondering whether fuel bouncing off it might be creating a bottleneck into the engine.

I was curious to see if I could improve the throttle's effectiveness with a simple transitional filler machined to smooth the abrupt step between the carb and the intake runner. Although a different angle of attack could have been selected, the one I used is shown in the second CAD drawing (the violet-colored filler). Although the filler changed the operating point of the main jet (it had to be leaned out compared with using no filler), and it raised the engine's steady state rpm, the throttle still had zero effect on engine speed.

The next attempt was to machine a plug for the carb body behind the Venturi that was bored to match the i.d. of the intake. A new .312" diameter throttle disk and shaft were machined to replace the original .490" disk. For a first test, I didn't extend the passage for the original idle jet through the plug which meant that all air and fuel would have to come through the Venturi. For now, I was only interested getting the engine to respond in some manner to the throttle.

Testing showed eliminating the step transition between the carb and intake dramatically solved the throttle mystery. With the throttle half open, the engine immediately started, and it finally revs up and down under throttle control as expected. The speed appears to change smoothly over the entire range of the throttle, although others' experiences would say there might be room for improvement at one end or the other with a second jet. The next (and hopefully final) step is to determine whether a second jet is actually needed and, if so, whether it should control additional air or fuel. - Terry


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## V22

Thanks for taking the time to post the R&D and associated CAD models Terry. Very interesting work and a great outcome. The plastic carb video was an eye opener in illustrating how the wet mixture is.


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## mu38&Bg#

Scale carbs are by far too large for the resulting displacement.


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## mayhugh1

I planned to drill a radial hole through the throttle-reducing plug in order to make the idle jet functional again although I wasn't sure if I'd be using it to add additional air or fuel. After playing with three different main jet needles, I finally decided to not make anymore carb modifications and to continue using it as a single jet device. Upon adjusting the needle for running at w.o.t., the carb seems to maintain a usable air/fuel ratio at idle. Surprisingly, the idle speed or quality doesn't seem to be very sensitive to the jet's setting. There's still some mysterious goings on inside that carburetor, but at least this time they're working in my favor.

With a fixed, and what feels like a barely open main jet, the engine will start and rev up to 4500 rpm and idle down to 1200 rpm. The exhaust noise is deceptive, and the engine sounds like it's running at less than half those speeds. I measured the flywheel rpm using both a mechanical and an optical tach and got essentially identical results. The engine was run at both these extremes in the second video. It wasn't totally unexpected, but starting is much easier when hot. The main jet setting is stable and once set didn't require further adjustment even during multiple runs over several days.

With the engine finally responding to its throttle, I took another look at ignition timing. I had been running earlier with only five degrees advance in order to eliminate kickbacks during cold startup. I may be overly sensitive to this issue, but an old Virago of mine cold started similarly, and I went through two starter clutches during the time I owned it. The cold startup procedure that I eventually adopted allows 10 degrees advance, but the kickbacks return if I try to add an additional 5 degrees. Cold startup begins with a few seconds of full choke cranking at part throttle and the ignition turned OFF. This preliminary step wets the induction system enough so plug firing is delayed until the flywheel's momentum has a chance to build while re-cranking with the throttle at idle and the ignition ON.

Being more accustomed to the heat build up in engines having more cylinders, the knucklehead's operating temperatures were a pleasant surprise. During typical three minute variable speed runs in 80F ambient air, the outside head and cylinder temperatures never exceeded 145F. The temperatures of the heads at the end of the second video measured less than 120F. The temperatures of the exhaust pipes are essentially identical, and they typically run some 15 degrees cooler than the heads.





This will likely be my last post on this build. I'd like to thank Draw-Tech for the drawings that were made freely available to us in the downloads section of the forum. The quality of those drawings are among the best we're likely to come across in the model engine community.

Of the readily available V-twin model engine designs, Draw-Tech's Knucklehead is the most realistic looking, but this realism comes at the expense of complexity. It's not a beginner's project, and it felt as challenging as any other engine I've built. Although a majority of its parts were made on my Tormach mill and Wabeco lathe, CNC is not a requirement. The most demanding machining steps included several drilling/boring operations that required careful compound angle setups, and those operations were best done manually.

The component with which I struggled most was the tapered crankpin. The crankshaft design closely follows that of the full-size engine, and it works well. Its machining would have been much simpler if I had fabricated the crankshaft before the crankcase. This would have allowed the widths of the crankcase halves to be adjusted around the finished crankshaft for a proper thrust clearance. The alignment sleeve described in the build should be considered a must-have for assembling the crankshaft.

Issues with any new design can be expected to turn up during early builds. On this engine, these included the oiling system and, of course, the carburetor. The oil system's capacity is excessive, and the pump can easily be reduced in size. I don't recommend trying to solve the problem with sloppy machining, since the addition of a pressure regulator seems to be an effective solution.

Some may have been put off from building this engine by the 'big bang' camshaft provided for it in the original drawings. After all, the 'Harley sound' is a big reason for building this engine. The replacement cam that I designed works well, and the documentation included in the build log should be sufficient for others to duplicate it. Coupled with the drag pipes, it creates a loud exhaust with the infamous Harley lope.

A starter motor is a nice addition to any model engine, and the gear motor that I chose works well and looks at home on the engine. The engine's starting torque required additional gearing beyond that in the original design as well as a one-way clutch. I used a system of sprockets and chains for the starter drive, but the cogged pulleys and kevlar belts used in the original design may work as well.

If I were going to build a second engine, I'd make three changes. The first is that I'd lengthen the cylinders about three quarters of an inch. I received a comment during the engine's initial assembly saying the engine looked a bit 'squatty' compared with a full-size Knucklehead. And now, with the engine completed, I have to agree.

The second change would be the addition of a crankcase vent tube to route puke oil to the engine's underbelly and onto the floor of the stand. The internal oil scrubber that I designed for the crankcase vent added to the dipstick doesn't work, and every run leaves some oil on the top of the crankcase around the dipstick. This requires installing an appropriate fitting in the side of the gearbox , but I'll likely wait until the gearbox has to be opened up for some other reason before it's added to this engine.

A third change would be a modification to the distributor to manually advance the ignition timing from 0 to 20 degrees once the engine is started and running. I believe the early Knuckleheads with their kick starters were provided with this as well. An ideal solution would be independent of the distributor's installation in the crankcase. The current 10 degree static advance doesn't leave significant performance on the table, but the engine's starting procedure would become more reminiscent of the early Harleys. - Terry


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## Scott_M

Outstanding !!  It sounds as good as it looks.
I cannot thank you enough for taking us along with you on this build. It is as impressive as any of your previous builds and does indeed set the bar. I have to admit though that I am a little saddened that it has concluded   I guess I will just have to wait for your next project.

Thanks Terry !! and congratulations.


Scott


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## napoleonb

Well done!


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## stragenmitsuko

It's been a wonderfull journey , thx for letting us tag along . 

Something I'v been wondering about with the way harley davidson designed their crankshaft  .
Maybe a little OT , altough the model expiranced thesame issue when the gears locked up . 

Imagine a knucklehead bike ,  with a typical harley-davidson  rider  and maybe a matching girfriend on the duo 
going up hill in the highest gear at relatively low speed with the throttle wide open .... Worst case senario . 





That would put a huge torque on the crank pin and the output side of the crankshaft tht drives the rear wheel . 
With only that taper to hold it . I can imagine the taper breaking loose given harsh conditions 
with all kinds of problems . If I was a designer , I would have used mabe a splined shaft with a taper 
or something similar .  Just brainstorming


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## minh-thanh

Hi Terry !
With you, this is 'A Work In Progress' , 
With me, all  'A Work In Progress'  you did , those are online lessons
Thank you for all !


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## mayhugh1

I've wondered about the same thing and agree there is some point at which the flywheels will rotate out of alignment. A locking taper is used, and the nuts used on the early engines are tightened a couple hundred ft-lbs, but engine rebuilders invariably find them out of alignment. Later engines had the tapered pin pressed into the counterweights and some racers even welded the ends of the pins to the weights. - Terry


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## Rozlo

That is an awesome build.  Thanks for sharing this great adventure.  Do you have any build videos?  That would be awesome to see.  Your next project is going to have to be awesome because you have set the bar extremely high.  Thank you again.

Bill


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## Draw-Tech

Hey Terry
First thank you for the complements on my design, but hats off to you, for the transformation of my piece of coal into the diamond you have created. Not to mention the fantastic, how to build documentation you have created. You have created a piece that should only end up in a museum. I am proud to be a small part of it.
Congratulations on a great build.
Jack
Draw-Tech


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## GRAYHIL

Hi All
A quick query
The flywheel starter pulley 3/32 slot is shown on the L/H side on the detail drawing but on the R/H side on the assembly drawing.
Which is correct?
Graham


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## mayhugh1

If you use the camshaft specified in the drawing package, the engine will run counterclockwise when viewed from the cam box side of the engine, and you would place your starter rope slot accordingly to start it. If you use the camshaft that I designed, the engine will run clockwise when viewed from the cambox side of the engine, (the same direction as the full-size engine), and your starter rope slot location would have to be reversed. Be aware that if you use my camshaft, the oil pump's inlet/outlet locations will also have to be swapped to accommodate the direction change from the original drawings. Best of luck... - Terry


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## GRAYHIL

Thanks Terry
I am making it to the downloaded drawings, so should the slot be on the right or left on that detailed drawing of the flywheel starter pulley?
Graham


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## mayhugh1

Graham,
I don't have access to the drawings right now, but in that case, standing on the flywheel side of the engine, you'll then want your starter rope slot on the left hand side of the pulley so that when you pull the rope upward, the engine will be rotating clockwise as the rope leaves the pulley. - Terry


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## GRAYHIL

Thank you very much Terry.
Graham


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## Jimbobob

Lloyd-ss said:


> Terry,
> I really appreciate the personal response, and do not want to hijack your thread, so I will only ask a tiny bit more, and then start a build thread so as not to impose on others. For the project I am starting (52cc diesel, horizontal, crosshead) I was planning to use 12L14 for the head (with water passages), 316 stainless for the valves, normalized 4130 DOM tube for the cylinder (with water jacket), purchased Tanaka 1.5 mm thick rings,  and possibly Nitronic 60 stainless for the piston (very good galling resistance and I have some of it on hand). Your endorsement of C544 for the valve guides checks off another box in the material list. I admit that I'd rather work with 7075 for the head, but it is a simple design so the 12L14 will still be easy to work. I am guessing that you will say that with a 12L14 head, either the  C544 or the 12L14 head material will be suitable.  Again, thank you so much for your response.  The freedom with which you and all the forum members share their knowledge is much appreciated.
> Lloyd


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## Jimbobob

What type of oil is used in crankcase for knucklehead motor


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## mayhugh1

Jimbobob said:


> What type of oil is used in crankcase for knucklehead motor


Lloyd,
I used 5W-20 as well as straight 3o weight. Don't see any differences. Your plans for your diesal project sound OK to me. Best of luck.

Terry


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## GRAYHIL

Hi All
Making sure and steady progress on my Knucklehead.
Just ordered the belts and pulleys from across the water in America.
A further query?
I presume the starter motor is always engaged even when the engine is running on petrol.!
Graham


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## mayhugh1

GRAYHIL said:


> Hi All
> A further query?
> I presume the starter motor is always engaged even when the engine is running on petrol.!
> Graham


Graham,
The original version was designed with the starter motor always engaged, but I added a one-way clutch to mine. 

Terry


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## GRAYHIL

Thanks Terry
Graham


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## dnalot

Terry your builds are fantastic. So whats next? 

Mark T


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## mayhugh1

dnalot said:


> Terry your builds are fantastic. So whats next?
> 
> Mark T



https://www.homemodelenginemachinist.com/threads/270-offy.31486/


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## GRAYHIL

The drawing of the camshaft shows:-
(Currently set up to machine key ways in camshaft but)
Center bottom, order of lobes on camshaft is different to that of top right picture.
Any idea which is correct?
Graham


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## mayhugh1

GRAYHIL said:


> The drawing of the camshaft shows:-
> (Currently set up to machine key ways in camshaft but)
> Center bottom, order of lobes on camshaft is different to that of top right picture.
> Any idea which is correct?
> Graham



Graham,
I remember running into inconsistencies in those drawings as well, but since I designed my own camshaft I never spent the time trying to figure out the machining of the original one. Are you really sure you want to stick with the original unproven 'big bang' cam? It isn't at all clear that such a cam will work with a single carburetor set-up. - Terry


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## GRAYHIL

Hi Terry
Designing a cam is way beyond my capabilities.
I will have to study all the drawings and come up with something? to guide me.
At the end of the day it will be used more for display at exhibitions than for running.
Still thank you all the same.
Graham


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## mayhugh1

GRAYHIL said:


> Hi Terry
> Designing a cam is way beyond my capabilities.
> I will have to study all the drawings and come up with something? to guide me.
> At the end of the day it will be used more for display at exhibitions than for running.
> Still thank you all the same.
> Graham


Graham,
You're welcome to use the one I designed. There should be enough information in my build thread to duplicate and install it. You can use the same pin mounting scheme described in the original drawings to affix the lobes if you wish. My cam will reverse the engine's direction of rotation, however, and this will require the oil pump's input and output to be swapped. - Terry


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## GRAYHIL

Thank you very much for your suggestion.
I will find the relevant pages and see if I can incorporate them.
Graham


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## GRAYHIL

Hi All
On the head drawings ref the position of the .25" valve holes , one is at .330" and the other is at .339" is this difference critical?
Graham


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## mayhugh1

GRAYHIL said:


> Hi All
> On the head drawings ref the position of the .25" valve holes , one is at .330" and the other is at .339" is this difference critical?
> Graham


You should be able to work with that...


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## GRAYHIL

Mayhugh1
I can work with that, perhaps I did not express myself clearly. I was asking 
why ?
Graham


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## mayhugh1

I'm not sure why the original designer made them slightly different you might email him. Do you have any photos of your progress so far?


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