# First engine, an RC aircraft 4 stroke



## digiex-chris (Feb 4, 2015)

Way back when I became interested in radio control models, I dreamed about designing, building, and flying my own engine. At that time I was pretty good with a hacksaw and a file, but that's all I had, so that dream sat and waited for 15 years. 

Now I'm equipped with a 10" lathe and an antique milling machine, and have built all of the tooling I'll need to do everything. It's time to start. A few weeks ago I put all of my knowlege and research together into a design, which I forgot to bring to work with me today to post for you. I wanted to document the build somehow, so I thought this might be a good place for it.

First step, I needed to make a quick modification to my mill to take the tooling I needed to use. My mill is a 100 year old Denbigh horizontal milling machine, that came with a relatively modern vertical attachment. The vertical attachment has a fantastically useful collet chuck, and an NMTB 40 spindle. The horizontal spindle is an odd taper. Does not match any known spec that I could find, including B&S, MT, and anything else I could look up. So if I was going to buy tools, it was going to be for the vertical attachment. Wanting to use those tools in horizontal mode too (because the vertical attachment doesn't have much space to the table), I needed an adapter. One $60 chunk of 4140 and a pile of hours taking light cuts on a lathe that wouldn't go slow enough, and this is what I've got.








Today I gathered all of the material together, printed out the drawing for the block, and set out to square up the rough stock. I had noticed a few days ago that things on the mill seemed loose enough to cause a few thousandths of rock when the table was cranked over to one side. so I decided to address that. Yup, I can pivot the table 0.005" over 14". The mill came to me with every surface of it painted, including the ways. I stripped all of that off, but avoided going any harsher than paint stripper and an aluminum scraper, so it's still kinda settling in and smoothing off. So instead of spending the day squaring up the block and boring two perpendicular holes, I spent it pushing and pulling and adjusting gibs. Still a good day in the shop.

All set up and looking good, I took a skim off the top, flipped the block, stuck a round piece of plastic on the moving jaw, tightened the vise, and took another skim. It looked like it took more off of one side than the other, so I checked with a square. Yup, the fixed jaw needs bigger bolts, I can easily push it out of square and off the base a bit. I wish I could find a 3-4" Kurt. The base appears square though, so rather than using the round plastic I just tapped the block down into the vise so it sat flat on the base. Within 0.001 over 2", I'm ok with that. These are just going to be cooling fins later on. The more critical set up later on I won't need the vise for.

Here's the shape of the main block that'll come out of that chunk of aluminum. I don't have a need for an open rear anymore, but I think I'll bore it straight through and put a plate on the back so that I can put a plexiglas plate on the back and watch the oil level and splashing.





 I'm planning on taking advantage of the horizontal mill in making perpendicular holes, by rotating the vertical head sideways to do the crankshaft bore, and without disturbing the setup, use the horizontal spindle to bore the cylinder (since I can lock the table axis and make it not succeptible to any table rock that might show up). That way I can get them perpendicular within the accuracy of the machine, which is quite good if I can keep the gibs where they need to be.

The horizontal spindle also makes it a piece of cake for squaring up the small end (the top and bottom, if oriented with a vertical cylinder). I just leave it on it's side in the vise where I did the last operation, rotate and indicate the vise in 90 degress, and install the fly cutter in the horizontal spindle. My vise isn't really deep enough to grab the bottom end of the block and face the top securely, especially with that tilting fixed jaw.


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## digiex-chris (Feb 5, 2015)

Got some holes bored. It's not very interesting.

Squaring up the end. There's a broken bit at the bottom of my knee screw so I can't get it high enough so I set the vise up on 123 blocks. A little sketchy looking, but it seemed to work fine.





Cylinder liner hole bored. I changed my tactic a bit realizing that I couldn't get the table up to center. I'll have to disturb the setup and indicate it in again. Hopefully as long as I put the same side of the block down, tap it down well, and indicate it in on the same edge using a 0.0001" graduation DTI, I can be as close as I want to be. Infact, I might be able to get more perpendicular than the mill is but it'll be fiddly I'm sure. I started with the cylinder liner bore because I'm not sure what this thin boring bar will do when intersecting a different sized hole, so I decided to do the one that needed to take the shrink fit first.





1.125" bore to take a liner for a final bore of 1".  .062 liner wall thickness? Is that going to be enough? It'll be 4140, so I'm guessing it'll be fine. I'll bore it, then put it on a mandrel and do the outside, then install it in the cylinder. I'll do the lapping once it's shrunk in there.


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## digiex-chris (Feb 5, 2015)

oops, I left the oilers turned on and went to bed last night. I just emptied 3 ounces of fresh oil onto the ground.


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## chipstractor (Feb 6, 2015)

The oil forgives you, continue.


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## digiex-chris (Feb 9, 2015)

That 3/8" shank 2" long boring bar wasn't doing the job. It narrowed down to 1/4" or less between the carbide tip and the 3/8" shank. I decided to modify my boring head to take my 5/8" shank boring bars. Much better. 1.625" crank case bore. It'll be a spacious crank case. I'm hoping to have a large sight glass in the rear case so you can look inside.





Was able to finish off the crank case bore with no squealing or chatter, and with a good finish, even where it intersected the cylinder liner bore. I changed the design a bit so the undercuts on the front and back of the block are now curved instead of having a flat top, so I can make the front and rear case covers entirely on the lathe in a single setup allowing good alignment for the bearing bores to the crank case. It also allows me to cut the undercut in the same setup using my well setup X axis, instead of using my Z axis. I'm not very confident in the knee gib setup at the moment and don't really want to operate with that axis unlocked. Being out of square 0.002" across the height of the block wouldn't be that bad in the direction I have the block clamped down, but I don't quite have enough travel with my current setup to sweep the face vertically with a fly cutter, but I can do it horizontally and avoid both problems at the same time. Either way, I want to do it without removing the piece from the setup that I used to bore the crankshaft hole. Feeding in a fly cutter from the right and leaving a curved termination instead of above and leaving a flat one should accomplish that.

I'll try to remember to get a render of that drawing.


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## petertha (Feb 9, 2015)

digiex-chris said:


> 1.125" bore to take a liner for a final bore of 1". .062 liner wall thickness? Is that going to be enough? It'll be 4140, so I'm guessing it'll be fine. I'll bore it, then put it on a mandrel and do the outside, then install it in the cylinder. I'll do the lapping once it's shrunk in there.


 
Newbie here. Working on this exact aspect & I did a table of comparable liners which I will dig up for you. Are you saying 1.125" cyl ID =~ Liner OD and 1.062" bore? If so, that's 0.0315" liner wall thickness. If I recall the comparisons correct, that's maybe on the thinner side, avg was 50-60 thou? Commercial 2-stroke-RC engines I've seen thicker yet, but maybe more to do with ports cut out, different materials used.

OTOH, I'm, not sure what factors into this & maybe thinner is fine? Maybe insurance against distortion during machining? My first test liner is 12L14 & something around & 0.059" wt. I machined the liner od to within 0.001", then work on the inside; drilled, bored & reamed bore. I couldn't measure any distortion in OD (was expecting some). But anyway that was my procedure. Now I want to try cast iron liner just to see the difference. 

Another 'newby discovery' FWIW. My leaving 0.0065" bore dia from reamer to lapping is way too much. I'm trying to match an existing bore (commercial piston ring actually) & that's just how the numbers shook out from closest reamer size. Lapping, I've found,  is very controlled but painfully slow even with coarse (150-220) grit to begin with. So next trial will be bore to within maybe 0.002-0.003" & lap to final from there. I still like the idea of a reamer for straightness & cleanup. I was committed to making matching piston rings I would target finished bore to 0.002" +reamer size & go from there.

Would like to see some of your pics & I will do the same.


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## digiex-chris (Feb 9, 2015)

Yeah I'm trying to get as many pictures as I can as I go, since I always have my phone on me. I tend to do all of my considering infront of a computer, then print out a plan and get to work machining with an audiobook playing. I'll probably be able to quote the job in units of completed audiobooks ;D

I've rebuilt a few antique two stroke RC engines by making new liners out of cast iron. I found it easy to do by starting with a reasonably thick chunk, thicker than needed, and turn and lap the ID first so you can bore it without having to worry about a thin wall distorting. then mount it on a close fitting mandrel, and turn the outside to the fit you want. The ID came out predictably. That's what I'm planning to do here. I decided to avoid anything cold rolled to avoid any internal stresses that could be relieved during boring. You won't have that problem with a cast iron liner, as long as it was well stress relieved (time or otherwise) before starting. I found cast iron easy to work with if you go slow enough. I also tend to leave only 0.001" for lapping if I can. Since I usually make pistons to go with my RC engine liners, I don't really care if I have to lap it slightly oversize to get all of the marks out.

The other way I could do it is make the liner OD, shrink it in, then mount up the block somehow and bore and lap the liner in-place. I think that might be overkill though. I'm going to measure well to see if that distorts anything but I think it'll be ok. If it does, it should be within what I can lap out.

I'm targeting a 1" bore, with a cylinder liner OD of 1.125", so 0.0625" wall. I'm thinking it'll be ok, it's around what I saw for one old OS that had a nickel plated brass liner. I don't really know what the concerns are though, other than problems manufacturing. Thinner might be better, to transfer heat to the aluminum easier?


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## WOB (Feb 9, 2015)

Have you considered a monoblock cylinder of 12L14 with fins machined directly into OD. and leaving a .062" wall bore?  Make the top fin extra thick so the head bolts have something to thread into and machine a 4 or 6 bolt flange on the bottom to mate with crankcase.  This design works well.  I have built two 4-strokes, a 9 cylinder Hodgson radial and a 4 cylinder boxer running on glow fuel. Both had 1" bores  and strokes were about 0.865" .   There were no problems with cooling at full load on a test bench.  Might be a tad heavier than a regular sleeve with alum fins, but not much and easier to make.  Besides, if you blue the cylinder it looks sharp against polished alum head and rocker boxes.


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## digiex-chris (Feb 9, 2015)

That's a really good idea. I haven't considered that. I definitely will consider that. If I screw up and have to make another block I'll definitely put some time into that, but I think I'm going to keep going with the aluminum cooling fins because I'm half done the block already and I intend to fly it, so weight is a concern. I've already eliminated a crank follower and another bearing from the rear with that goal in mind, to favor of driving a timing belt off of the front half of the crank.

You've also got me thinking about what the minimum thickness should be in order to make the top fin take enough bolt threads to be secure enough in aluminium. If I can do it with the top fin, I wouldn't need to leave a thicker wall in the aluminum block and it would be a simple parting operation once I mount it on a mandrel. Is there a minimum number of threads to keep in mind for aluminum? I've got 4 #6-32 bolts in mind for the head.

Also, while I'm thinking about cooling fins, is there a minimum temperature my cylinder should be reaching? I imagine I should I avoid over-cooling it, but is there an ideal target for a model gasoline engine for performance reasons?


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## digiex-chris (Feb 9, 2015)

Current design iteration. I expect it'll change again until too much cutting has happened. I keep cutting and cutting but it's still too short! 

I'll probably round the top corner of the front cover with the cooling fins. Might as well make it flush with the front too.














The piston design is changing. I need a longer skirt and to space the rings out a bit more, and put the oil ring near the bottom.


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## Swifty (Feb 10, 2015)

For the amount of screw engagement required, as a rule of thumb, I've always used 1.5 times the screw diameter as a minimum. Of course more is better, but with this you will get a reasonable amount of engagement.

Paul.


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## gus (Feb 10, 2015)

Swifty said:


> For the amount of screw engagement required, as a rule of thumb, I've always used 1.5 times the screw diameter as a minimum. Of course more is better, but with this you will get a reasonable amount of engagement.
> 
> Paul.




Useful info but ''Born Loser Gus''  been using 3 x d as thread length engagement. Will tune back to 1.5---2 times for aluminum. I have have stripping threads. Possibly due to burrs from sawing fasteners to length and not well deburred. With the Howell V-2,will follow Jerry's thread length requirement.
Just bought Japanese ''SKC''  6-32 tap which is part of a complete set of taps and dies.


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## vederstein (Feb 10, 2015)

Thread engagement is a topic I learned in engineering school all those years ago.  Without going deep into the math, the stress on the thread is the cross section of the thread form, not the bolt minor diameter.

When the calculation were done, it was demonstrated that the first three _full_ threads took some 90 percent of the load with the fourth thread having sufficient holding power to break the bolt and not strip the thread.

So there you have it:  four full thread engagement.

(But anything more certainly doesn't hurt)

...ved.


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## digiex-chris (Feb 10, 2015)

vederstein said:


> Thread engagement is a topic I learned in engineering school all those years ago.  Without going deep into the math, the stress on the thread is the cross section of the thread form, not the bolt minor diameter.
> 
> When the calculation were done, it was demonstrated that the first three _full_ threads took some 90 percent of the load with the fourth thread having sufficient holding power to break the bolt and not strip the thread.
> 
> ...



Thanks! Was that in steel? I noticed nuts often have only 3 or 4 threads, and now I understand why.


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## digiex-chris (Feb 10, 2015)

Yesterday's progress. Front and rear recesses cut.









Time to run down to the post office and grab the steel for the liner and do a bunch of lathe work on the front bearing holder.

Going to have to start planning out a head soon. 4 valve DOHC, or 2 valve DOHC? I want to use double camshafts so I can easily play with valve timing and get some more familiarity with that. Going to use a 1/4-32 spark plug, but still that's not going to leave much space in a 1" diameter bore. I'm thinking with the air not scaling problems, it might be better to use fewer but larger diameter valves than lots of tiny holes. All I know is it's rare for commercial aircraft engines to have more than two valves, but that could be for economic manufacturing reasons, or weight reasons, or price point reasons. 

I'm having trouble searching down resources on that matter, so any comments would be appreciated.


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## gus (Feb 10, 2015)

Hi Chris,

Gus will watching every move you make. Another engine on my list. 

Crankcase/engine block coming to shape. Take your time. You have come so far.


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## digiex-chris (Feb 11, 2015)

Time to think about the liner a bit more before I start making chips. I might attempt to thin out the middle of the connecting rod a bit so that it won't contact the cylinder liner at all, and I don't need to make that notch. If I make it a round cross section, the notch could be very small and simple. If I don't need to cut that notch, my mandrel to hold the thing gets simpler. I might also be able to get away with just filing some clearance into it. The notch was originally a compromise so that I could keep the total height of the engine as low as I could. 1/4" taller and that problem goes away, but I'm not willing to do that. The piston skirt could also peek out the bottom of the liner a little ways and probably be ok, it's only 0.150 on the cylinder length and only maybe 0.025" into the cylinder wall that I need.

The major trouble is that I can't (or don't want to) really remove the liner to test the fit once I shrink fit it in there. Eliminating a notch eliminates having to position it while rushing to install a shrink fit and then figuring out how to adjust it if I need more clearance later.

The next idea I just had was make a steel connecting rod. Could be significantly thinner. The 7071 connecting rod might be more than strong enough to thin it out some as well. 

What are the major stress points on a connecting rod? Are there any other than compression and tension in the center of the rod? Are there any bending forces? I imagine the greatest stress is elongating or pulling open the rod ends.

The #6-32 spiral flute taps come in Friday, so I can always take a break and work on the front and rear cases while I think about that.


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## petertha (Feb 11, 2015)

I encountered some similar issues for this radial design when I detected link rod interference with the liner. Its kind of geometry dependent, but in my case I was able to tweak a few things that collectively got it corrected
- slightly shortened the liner portion that extends/mates the crankcase hole (the excess wasn't doing anything useful beyond the contact area anyway, the piston doesn't run down there)
- chamfered vs notched the liner ID skirt at specific dimension (easier to do in lathe mode)
- slightly reduced the width of link rod & chamfered the corners to accomodate
- plan to make link rod of 7075 aluminum for strength

In terms of the liner fit, my prototype seems to have worked out according to plan. The liner is about 0.0005" interference. To assemble, I put cylinder in 350F oven, liner is room temp. Drops in place & remains firmly in position. That's the easy part. To remove, I pout assembly is same oven, aluminum expands more than steel, liner dropped right out no problem. Also I did not detect appreciable bore change of shrunk liner, but to be safe will do final lap in-situ. The general idea was to be able to replace a liner & not throw away the cylinder portion. Hope this helps (learning myself)


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## digiex-chris (Feb 11, 2015)

thanks, that's extremely helpful! Similar bore, so I should be able to use your numbers for the shrink fit. I was going to go for 0.0015 over, but maybe that's too much. I like the idea to have it drop out so I can make adjustments later. I've made mistakes in the past that have caused excessive and fatal wear to a cylinder, and this could help minimize rework.

I think like yours, I can do some small cumulative things to deal with it. I can then deal with the connecting rod if there's interference later. It's close enough. The chamfer at the bottom is way smarter than notching!


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## digiex-chris (Feb 12, 2015)

I use a chunk larger than necessary to do the cylinder liner so that the 3 jaw chuck doesn't distort it any amount that I care about. Grab it in any old chuck, 





and pop a bore in it. 





Oversize by 0.001". Darn. Not that it matters, I can just make the piston to fit whatever I end up with and it's well within range of my lap. I was hoping warm up my skills before it got more critical but I guess I got impatient. One more skim kit before taking my second-to-last measurement would have pulled it off right. I guess it hit my goal of re-aligning my boring bar expectations...

The liner ID is done (but not lapped, going to do that when it's installed in case it moves a bit when cutting the OD). It has about 0.0005" taper getting narrower towards the headstock, as expected from my lacking one of the two spring cuts I needed before hitting my size and the setup of my lathe. Again, well within the ability of the lap to fix.





And then I spent the rest of the evening making an expanding mandrel that I can operate through the crank case hole when the liner is installed in the cylinder, so I can turn the cooling fins without having to make an additional mandrel to hold it separately from the liner. I'll have to be careful to remember order of operations so I can take a skim on the mandrel to fit the cylinder liner, finish the outside of the liner, install the liner into the cylinder, mount the cylinder and liner back on the mandrel, and turn the cooling fins before removing the mandrel from the lathe.

I'll probably take a break on the liner and make the front and rear cases next, so that I can drill all of the bolt holes in the cases and crankcase at the same time. I don't think I want to be grabbing the cooling fins in the vise in order to do that later, so I'll do that before the cooling fins are formed.

Time to go find a box and some plastic bags. I've got more parts than 1 now, and they're starting to walk around the shop and hide.


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## digiex-chris (Feb 13, 2015)

I wanted to install the cylinder liner into the block and turn the fins for something to do while I waited for my bearings to come in for the front cover. Since I didn't want to grab the relatively fragile fins in the vise, I decided to finish the lower end of the block now. Gus showed off using an angle plate, reminding me that I had one. Unfortunately because mine is cheese grade cast iron without a rib to stiffen it, I can push about 0.004" flex at the top of the 5" height. Oh well, it'll be fine for drilling a few bolt holes. Better than my drill press anyway, and better than trying to grab the bottom (top in this case) of a tall skinny object in my cheesy vise. No, that's not the only clamp I used, I'd just taken the clamps off and remembered to grab a picture. The toolmaker's clamp was used as a fence so I could flip the part around and get it close enough for the dial indicator to sweep the bore without much adjustment. On the front of the angle plate I'd stacked parallels and a 123 block so I wouldn't have to dial in the vertical face. 





Back to the mandrel. Here's how I did it, after getting an example from a retired machinist family member. Make a 7 degree taper. Make a plug with a matching taper. Bore the start of the hole slightly larger than the thread major diameter, to allow a roll pin to fit in there. Cross drill your bolt for the pin. The pin then pulls the wedge out when you back the bolt out. The bolt head (actually a nut silver soldered onto fine thread rod, but same thing) needed to be turned down a bit, I underestimated how far in the plug would go before locking up on my cylinder. Warning: wobbly hack saw cut!





I put a slight amount of tension on the plug, then took a skim down to a perfect sliding fit on my cylinder liner. Then parted the back about half the depth to the counterbored roll pin clearance hole.





The ends are cleaned up





And 0.003" oversize. I was getting tired so I decided to make the final shrink fit dimension the next day when I'd had more sleep and the correct amount of coffee. It'll give it a chance to equalize temperatures too. That 4140 got a little hot from the roughing passes.


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## digiex-chris (Feb 13, 2015)

p.s. if anyone's curious about what a horizontal mill can do that is harder on a vertical mill, imagine facing that angle plate with a fly cutter. You'd need a really deep vise, and one that tolerates an angled part (the angle plate has some draft). Or use another angle plate that's already been proven square and dial it all in horizontal, adding some margin for error. 

Such an easy setup on a horizontal mill. I think I'll bolt some ribs to that plate and do just that.


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## digiex-chris (Feb 13, 2015)

I've got an ignition system from an RC gas two stroke, designed to fire once per crank rev. Does this mean I should be running the magnet and sensor off of a camshaft? Or will it work ok if I let it fire every rev and waste a spark at the top of the exhaust stroke?


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## Swifty (Feb 13, 2015)

digiex-chris said:


> I've got an ignition system from an RC gas two stroke, designed to fire once per crank rev. Does this mean I should be running the magnet and sensor off of a camshaft? Or will it work ok if I let it fire every rev and waste a spark at the top of the exhaust stroke?



On my Nemmet Lynx engine, I have a wasted spark on the exhaust stroke. But, I have 2 magnets set up on the end of the camshaft, this is so the CDI knows how fast the engine is going and can use auto spark advance. If you don't have auto advance, you can get away with one magnet on the camshaft which will only fire on the ignition stroke.

This was all pointed out to me by other members here, they were all so helpfull.

Paul.


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## digiex-chris (Feb 13, 2015)

that's a good point, it's an auto-advance CDI. 2 magnets on a camshaft it is!

Thanks!

That gets me thinking...Maybe I can repurpose the timing belt tensioner for this. Make it 2x the crank pulley and drive it, and stick 2 magnets in it.


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## Swifty (Feb 13, 2015)

digiex-chris said:


> that's a good point, it's an auto-advance CDI. 2 magnets on a camshaft it is!
> 
> Thanks!
> 
> That gets me thinking...Maybe I can repurpose the timing belt tensioner for this. Make it 2x the crank pulley and drive it, and stick 2 magnets in it.



If you use the tensioner, just make sure that you can easily adjust the timing.

Paul.


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## digiex-chris (Feb 13, 2015)

Starting to look like my imagination now. 

What's for dinner? 





Engine block.

Sleeve in








Back on the lathe on the undisturbed mandrel.





Borrowed the wife's lightbox.


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## Swifty (Feb 13, 2015)

Looking very nice, I'm a great fan of shrink fitting.

Paul.


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## digiex-chris (Feb 14, 2015)

yup, slid in easy, and once cool it didn't move a single bit from the fin turning. Thanks for the guidance.


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## digiex-chris (Feb 14, 2015)

darn, I forgot to provide some way for the head to locate on the cylinder bore. I guess I'll use dowel pins or an external fixture for alignment while torquing the head bolts if I don't like the bolt slack. I guess I can always take the liner out and shave a bit off the lip to make a recess for a copper gasket and head location.


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## digiex-chris (Feb 16, 2015)

I took a break from cutting metal and spent a few days modelling more parts of the engine. I've got some questions about where I'm going to mount magnets and sensors for the ignition, so I'm going to make sure I don't need either the front or rear case as a mount point before I start making them. That means I need to plan out the whole head, valves, and camshaft location.

So far I've got a slightly domed head, which took forever to figure out the 90 degree tangent to make the valve guide line up perfectly. Shim over bucket style lash adjustment. .427" diameter valves, and when the port under the valve area is considered, the area matches the inlet and outlet diameters of .321". 0.100" lift gives me 4:1 diameter to lift. The result? Looks About Right, I think. I'll give it a shot. 

The CAD program is estimating 1.2 lbs right now. So I'm a little over what a Saito in the same size range weighs, and it'll grow a bit still. This is including a hefty mount though, and saito doesn't include the mount or muffler in their weight spec.













My crankshaft is .472" (funny how that worked out, .427" valve, .472" crankshaft), I might narrow that down after the bearings to cut some weight. It's hollow, so I don't know how much I can gain from that. I'll probably just try it and see what happens.


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## Charles Lamont (Feb 16, 2015)

Those are nicely rendered, what CAD package are you using?


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## digiex-chris (Feb 16, 2015)

it's the student edition of Solid Edge


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## hussien95 (Feb 16, 2015)

Very nice engine

I can not wait to see it works

Good job


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## tornitore45 (Feb 16, 2015)

I came late to this party but like this engine a lot.
Would you make the drawings available when you are finished?


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## digiex-chris (Feb 16, 2015)

Absolutely. I've been updating the 3d model and drawings to reflect changes as I go. I can't promise the drawings will match drafting standards but at the very least I add dimensions in as I find them missing.


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## digiex-chris (Feb 17, 2015)

I spent some time with the rest of the head in order to get an idea on valve timing. I decided to copy the Whippet plans i had for the cams and valve timing since it was the same bore, stroke, and RPM target, which means each valve tilted 55 degrees from vertical at TDC to set the timing and a little bit more duration to the exhaust than the intake. Since I had all of the related parts linked together to check that, I made a little animation showing the cycle. After I noticed the exhaust valve collision, I realized the tilted angle of the valves throws off my timing marks. I need to tilt each valve an additional 18 degrees. This means currently, the exhaust cam is 18 degrees delayed and the intake is 18 degrees advanced.

[ame]https://www.youtube.com/watch?v=wH086IyOouw[/ame]

Any ideas how to attach the pulleys to the camshafts? I'm considering broaching a square hole in the pulley and using a bolt and a washer to pull it against a shoulder on the shaft. It's not adjustable that way but I think I can pretty accurately estimate the distance between pulley teeth separated by the belt. I think I'm going to put the ignition magnet wheel on the end of one of the camshafts, sandwiched between the pulley and the camshaft shoulder, but not running on the square. Clamping force from the bolt holding the pulley on should hold the trigger wheel I'm hoping.


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## tornitore45 (Feb 17, 2015)

Thanks, will stay tuned.


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## petertha (Feb 17, 2015)

Nice animation. Is it an optical illusion or is the piston hitting the valve near the top of the stroke?


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## digiex-chris (Feb 17, 2015)

Yeah its totally colliding. The timing is off by 15 camshaft degrees or so.


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## digiex-chris (Feb 19, 2015)

Ok I'm comfortable with how things fit together now. Going this far in CAD before cutting stuff has avoided a few junk parts already, and was worth it. The pulleys were too large and intersecting. Now it's fine. I'm going to start on the front crankcase tomorrow.


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## mattty (Feb 20, 2015)

Love the old mill, really enjoying the build.


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## digiex-chris (Feb 20, 2015)

mattty said:


> Love the old mill, really enjoying the build.



100 years old and there's probably 100 years left in it.


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## digiex-chris (Feb 23, 2015)

I managed to forget to get pictures of making the entire front case cover. Sorry!

After turning the front case, I drilled the bolt holes on the mill. I screwed up the setup and didn't have enough range on one axis to drill the last two holes, so I'll get them when I set it up to cut the scallops.





I keep finding uses for the Taig chuck adapter I made for my larger lathe. The soft jaws were just the tool for grabbing on to the thin edge behind the o-ring. 

On to the rear case





Drill some holes





Done! (for now)





I'll saw off some of the excess, then set it back up with the boring head set at the right radius and cut those scallops between the bolts by pretending I'm boring a hole. 

It's still pretty heavy. I think after I'm done with the crankcase I think I'll put it back on the mandrel and trim off half of the thickness of the cooling fins. At that point there will be no need to clamp on the fins anymore so they won't be structural in any way.


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## digiex-chris (Feb 24, 2015)

Wow that was miserable. Setup to cut the scallops, and the first one I didnt' check surface finish till I was 0.007" from dimension. I needed to sharpen and adjust the angle on the boring bar. Managed to pull it off. Switched to the other side, and I jerked the handle which fed too fast and snagged the rear cover, shearing the corner off and shifting the part on the table. Luckily it only took a corner off that I was going to remove anyway. I dialed it back in, and snagged it again!

Finally, I got both sides cut and called it a night without having to re-make any parts. I should have 1) gotten more sleep and 2) clamped some 123 blocks on either side to add a little more stability to the setup.


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## digiex-chris (Feb 24, 2015)

After giving myself 3 more chances to ruin 30 hours of work, the block is done!























Now I'm going to start on the crankshaft. Thinking about using a ball end mill to cut a groove in it, then a matching groove in the pulley, then using a spring roll pin to lock it in place on the crankshaft, rather than fussing with fitting a square key or some other method of positive engagement.


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## digiex-chris (Mar 3, 2015)

A remastered version of a favorite decade and a half old video game was just released, so I took a break for that. Time to regain my momentum on this project!


Connecting rod time. I decided I needed a connecting rod before a crankshaft because I can't depend on my reamers to give me a specific size. This time was an exception in that they went 0.008 oversize on one hole! I must have hit the bottom of the hole hard or something. Regardless of technique, they seem to be slightly oversize  (0.001") and I haven't really figured out by exactly how much. I bought a set of hole gauges to help out with that.

Make a bit of a mess turning some round 7075 into flat 7075, with the bushing bores drilled and reamed.




Large end bushing, 0.0005" larger than the bore. It would have been majorly sloppy if I'd went by the size on the reamer box. Glad I measured. Oilite, but I neglected to read about machining it so I'm sure I've smeared the pores over. It's ok, this will be well lubricated anyway.




Large end bushing shrunk in. I only singed my fingers slightly. Tip: Aluminum at 350F does not look any different than aluminum at room temperature.




Both bushings shrunk in, and flycut to width. Scribe some lines just to keep a track of how close to disaster I'm coming with the next setup







I just need my brain (which I don't seem to be in control of unless I'm almost drifting off to sleep) to finish figuring out how to do the rest of it.

I think this will be the plan. I'll start on the big end intersection between the curved rod end and the flat angled side, with the flat angled side dialed in parallel with a mill axis. Then I'll mill that flat, lock the mill down, rotate the dividing head 256 degrees forming the big end curve, and stop. Then I'll remove from the fixture and swap ends 180 degrees so the little end is concentric with the dividing head, dial the opposite flat parallel with a horizontal axis, cut the opposite side flat, and the small end curve (still to be drawn and number crunched). 




Sounds pretty good in my head. I eliminated the dipper, I don't think it'll be necessary and it'll complicate it a lot.


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## digiex-chris (Mar 5, 2015)

Looks like it's working!





Got through making the big end, then I realized two things.

1) I made that drawing not including the bushings, so snapped the lines tangent to the wrong circle. I wanted the bit between the ends to be a little thinner than that, closer to the scribe lines. But it was so easy to get lined up, I'll probably just do it again. The nice thing about the fixture is you can pull the part off to look at it without losing your spot.

2) my DRO started jumping all over the place once I was done with the dividing head for the curved part of the big end. Gotta go in and find the wiring fault. I can make it stop misbehaving with pressure on the cable end, so I'm hopeful I'll be back on track friday.

I'm going to test my bead blasting setup on the connecting rod since it's mostly hidden from view.

Time to readjust those spindle bearings again. Still sneaking up to the ideal clearance.


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## Brian Rupnow (Mar 5, 2015)

Your solid models are great!! Your pictures are way, way too big. Use a resizing program to post the pictures smaller. If you post them the current size we have to scroll back and forth and up and down just to see one image.---Brian


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## digiex-chris (Mar 5, 2015)

sorry, I didn't realize the forum wasn't resizing the image automatically for everyone. It shows a bar that says "This image has been resized, click this bar to view the full image" for me, and if I click that, I see the full size and can click the bar again to collapse it again. I'll start linking smaller sizes.


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## digiex-chris (Mar 5, 2015)

Brian Rupnow said:


> Your solid models are great!! Your pictures are way, way too big. Use a resizing program to post the pictures smaller. If you post them the current size we have to scroll back and forth and up and down just to see one image.---Brian



Is this size better or still too big? Looks ok on my screen but I don't mind going smaller if the average screen here is smaller.


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## Cogsy (Mar 5, 2015)

Brian Rupnow said:


> If you post them the current size we have to scroll back and forth and up and down just to see one image


 
There seems to be a funky forum glitch that causes this for some people on some threads. It happens to me from time to time, and it's always the same threads while others are fine.

As of now, this thread has never caused me an issue - all the pics fit on the screen and have the little 'resize bar' on them. Obviously it's not happening for Brian though.

It's a pain when it happens but I'm not sure we can do anything about it.

Edit to add - the resize bar shows this latest picture to be exactly the same size as previous pics - 1024x768.


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## digiex-chris (Mar 6, 2015)

Yeah I went back and added smaller sizes to them all, hope it helps


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## digiex-chris (Mar 7, 2015)

first major errors today! I quite accurately hit the dimension I held in my head, but unfortunately the dimension was for a different part of the connecting rod, so I cut a flat too far. It had dug into the bearing surface too far to be salvageable, so I decided to start over. I didn't have any 7075 left, so I decided to switch to 6061.

And then something happened that I'm not entirely sure of, maybe I bumped the vise on the drill press. The reamer grabbed the hole it was half into, picked up the vise, swung it all around one rev, and threw the vise across the bench.









I'll run to a friend's place on Monday and grab more 7075. I'll need to order more bearing bronze too, making new bushings will leave me with not quite enough to do the bits that go in the head.

I've got a few fixtures to make for the crankshaft, so I'll start on that while I wait.


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## barnesrickw (Mar 7, 2015)

Stuff happens, push forward.


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## digiex-chris (Mar 9, 2015)

yes! a friend had enough 7075-T7 (Nice and hard.) to make a pile of connecting rods. With the reamer cut short it runs true. I'll stick it in a collet and keep going.


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## Brian Rupnow (Mar 10, 2015)

That picture size is much better, thank you.---Brian


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## digiex-chris (Mar 19, 2015)

Woo a workable conrod! I had to make 3 of them for the junk bin before I got one that I didn't mill too far into the bearing end. It's nowhere near pretty. It's too difficult to do a rotary table style end with my slow maximum rpms on this mill. Breaking 1/8" endmills all week. if this thing starts up I'll make another conrod with a different method. I think it'll be fine for the troubleshooting step anyway. It at least gets me a reamed press fit hole that I can make a crankshaft for.

The crankshaft will have a hex to drive the lower timing pulley. Partly because I want to do something a little different, partly because I want to use a pulley so small I can't use a reasonable key, and partly because I wanted to try out the poor man's rotabroach.

I need to cut a pulley blank before I do the crank, so I can match the crank hex to the hole. That means a hex hole needs to go into a scrap of aluminum. They don't make a rotabroach in the size I need anyway. I saw this method somewhere on the internet, and I have to apologize for the inventor of it, because I can't remember where. Cheap, took me a couple of hours because my milling vise sucks and doesn't like to repeat.

Start out with some drill rod. Mine is 1/2", for the size of hex I was making (.349" across the flats). I used a hex shaped block with a reamed hole and a cross drilled set screw hole to hold it pointing upwards in my milling vise, to cut the flats on it. Cut flats giving the end approximately 7 to 10 degrees relief. Then throw it in a collet in the lathe (or make it run true in the 4 jaw, which ever you like), and dish the end of it. Some prefer to dish the end first, but I didn't like trying to debur the dish after the hex was milled, and prefer to debur flat faces. Flip it around, and drill a deep dish in the other end. I used a large center drill.

Chuck up another chunk of the same drill rod in the 4 jaw, and offset it about 0.020 TIR (it would probably cut faster at about 0.040, I think there's enough relief on mine to get away with it). Then sink a deep dish with that center drill again in this side.

Harden both as you see fit.

The offset end goes in your drill chuck, and the hex end does the cutting. The ball bearing gets trapped between the two. As the work rotates (or the offset end rotates, whichever machine you're using), the cutting edges of the hexed end take turns pushing forwards a couple of thou at a time. Drill a hole of your flat to flat dimension, or slightly larger. Drill a clearance step of your tip to tip diameter, to allow the hex cutter to start straight. That's a major advantage of a rotabroach, it'll start straight without that step. 

Grab a 1/2" ball bearing (or so, was right for mine). Trap the ball bearing between the offset part held in the tailstock chuck, and the opposite end from the cutting edges of the cutting part. Use a high pressure grease on the ball and start the hex end of it in the relief hole. Then hit the gas on the lathe and start advancing the tailstock.

Eventually, it'll cut the corners out. Surprisingly quickly too.


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## digiex-chris (Mar 22, 2015)

I forgot an important part of making this tool. Rather than bringing the dish on the end right out to the tips, it should be brought to the flats instead, and then using a dremel or a file, file the end relief out to the tips and the flats. It shouldn't have a scalloped edge like the above photo does. 

So, 2 more for the junk box, 1 more for me, and I've got a good poor man's rotabroach and a female hex template to assist with the  crankshaft. I'll use a carefully threaded 5/16" stud for the prop shaft, because I will be flying it and if I goof up and bend it with an "unexpected landing", I want to replace it easily instead of bending back a shaft.


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## digiex-chris (Mar 23, 2015)

While fiddling with the female hex template I noticed 3 flats were short. Upon measuring, I confirmed that two opposing sides were 0.005" too close and another 2 were slightly too far apart making the hole slightly egg shaped. I realized it was because the reamed hole I'd put into a hex bar as the fixture to index the drill rod wasn't centered well enough. I'd avoided using my dividing head for this task because it didn't have any indexing plates. So I solved that today. I didn't have any 5" plate, but I did have 4". Going with 18 holes allows me to divide 6, 18, and 36, which I'll have to do for this project. I haven't figured out how to make the sector arms work, it seems to be missing pieces. It's easy enough to divide 6 without them though, it always landed on the same 3 holes.





And then it was easy to make an accurate broach.


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## digiex-chris (Mar 23, 2015)

Well, that dividing head was worth making a plate for. Chucked up a piece of 4140 HTSR on the lathe, turned down the part that will be the hex of the crankshaft, and transferred the chuck to the dividing head. Good fit with the template. I'm happy. It took me all day because I had to true up my chuck adapter on the dividing head.

















Now all that's left is all the rest!


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## digiex-chris (Mar 26, 2015)

While I'm busy making a crankshaft, I've started thinking of the cylinder liner ID. I'm used to tapered lapped cylinders for two stroke model engines without piston rings. This is the first engine I've dealt with that has piston rings. I don't have any in my collection to measure. Should the liner still be tapered if I'm going to use piston rings? When the top of the bore expands slightly, the rings will have to spring open slightly. Is this a problem or am I asking for a stress fracture?


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## petertha (Mar 26, 2015)

To the best of my knowledge, liners for ringed 4S model engines should be parallel, not tapered like ring-less 2S. The ring is providing the seal, not the piston/liner squish.The two new OS-4S liners I measured were within 0.0002" (tighter at the top) but that could be manufacturing intention or measurement error. The 4S piston requires annular gap & appropriate allowance for the ring.  I'm just embarking on this myself do take it FWIW, but I think there are 2 primary paths:

1) make the liner to your preferred bore dimension, then design the ring & piston dimensions around that. Most refer to the Trimble method or its variations. Lots of web references & this forum. This method also requires a specific ring opening dimension to be 'heat set' so the compressed ring imparts uniform radial pressure. Again, lots of varied opinions & experience on this particular aspect. 

2) buy a commercial ring and ideally have access to its liner bore specs & its piston. Target match the liner bore to that & mimic the piston groove dimensions.

Myself, I'm pursuing (2) to avoid (1) for now  
I built a spreadsheet using Trimble method just to mess around & check against commercial rings for my own interest. I could punch in your numbers just to give you a reference, but you really need to see the SIC articles to digest what they are saying.


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## digiex-chris (Mar 26, 2015)

petertha said:


> To the best of my knowledge, liners for ringed 4S model engines should be parallel, not tapered like ring-less 2S. The ring is providing the seal, not the piston/liner squish.The two new OS-4S liners I measured were within 0.0002" (tighter at the top) but that could be manufacturing intention or measurement error. The 4S piston requires annular gap & appropriate allowance for the ring.  I'm just embarking on this myself do take it FWIW, but I think there are 2 primary paths:
> 
> 1) make the liner to your preferred bore dimension, then design the ring & piston dimensions around that. Most refer to the Trimble method or its variations. Lots of web references & this forum. This method also requires a specific ring opening dimension to be 'heat set' so the compressed ring imparts uniform radial pressure. Again, lots of varied opinions & experience on this particular aspect.
> 
> ...



Any chance you could share your spreadsheet? Looks like a really handy tool. I'll check if my stack of SIC has those articles.

.0002" sounds to me like a tolerance on a drawing requesting parallel. I'm used to seeing more in the neighborhood of 0.001" per inch on 2 stroke tapered lapped fits.


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## petertha (Mar 27, 2015)

digiex-chris said:


> Any chance you could share your spreadsheet? Looks like a really handy tool. I'll check if my stack of SIC has those articles..


 
Ultimately yes. Right now its a cobbled mess & mostly hard-wired pertaining to my own engine design. So its not quite ready for prime time. I'll be posting some questions to folks already using the Trimble method & thereafter it could be a handy general tool which I'm happy to share. 

When you read the SIC articles, you'll see his methodology & his reference to 'being within' 3 constraint curves. That's the part I creatively fudged by 'digitizing' the plot with three y=mx+b intercept equations in order that my own ring parameters could overlay & essentially replicate his plot in Excel. Then I subsequently found another article where the fellow 'computes' the curves from metal input properties which (my understanding) Trimble straight-line simplified. This aspect gets a bit deep & I suspect way overkill. I probably wont go down that path, it was more for personal curiosity.

Anyway, blah-blah. To give you a starting reference, the only thing that's required is the finished bore size. Everything drops out of that. If you tell me your bore, I could just post reply the basic ring results parameters. But as mentioned, you really need to see the original articles to make sense of it. BTW the math itself is dead easy. I was more curious how commercial rings were comparing to this method.


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## digiex-chris (Mar 27, 2015)

It does look pretty easy. I'll go see if I have a copy of those articles and start there. 1" bore if you're curious. 

Also, this article was very enlightening for me. 

http://modelenginenews.org/techniques/piston_rings.html

I think my plan is going to be follow the trimble method to arrive with a ring with a width 0.002" larger than a ring that would be for my bore, then squeeze it between discs on a mandrel at that 0.002" oversize diameter, and lap it back to my bore diameter so I can be sure of arriving at both the correct wall pressure and the correct diameter.

Have you found any information on oil scraper rings on model engines? I'm probably not going to bother at first, but it's fun to think about.


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## petertha (Mar 27, 2015)

Here's my calcs for 1.000" bore. Don't make anything until you digest the SIC articles!  Actually, let me know if you derive dimensions other than these in case I have boo-boos.

In terms of oil rings, that's where the article got a bit fuzzy for me. I kind of roughed in what I thought he was doing & left it there because my engine is methanol oil pre-mix, so N/A. There's 2 references I can think of, Terry who built the Hodgson 9 & 18 radials documented here on HMEM. And Rons Offy which used Trimble compression ring methodology so I assume oil control as well. There are probably others too, these are just what I recall.
http://www.ronsmodelengines.com/Offy.html


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## digiex-chris (Mar 29, 2015)

A successful, though cosmetically imperfect crankshaft. 

I decided that it would be a shame to ruin it after carefully milling a nice hex on it, so I made a little offset fixture to gain a little more purchase and bearing surface than any of my chucks could provide alone, while still avoiding marking the crankshaft. Then I simply dialed in this fixture in the 4 jaw, and turned the crank pin while supporting the end of the crank pin with the tailstock. This worked well.





To mill the crank web cutouts I clamped everything in my vise, then clamped down the v-block so it couldn't move. Then I ran a dial indicator across a rod turned to fit the crankshaft through-hole tightly, necked down to match the crank pin, and compared the reading to the crank pin. I rotated the fixture until they matched.








I got too greedy when milling the balancing cutouts on the crank web, and grabbed. The strength of 4140 prehardened shined, so it sheared the anti-rotation pin and spun the crank around the bearing journal a little ways, without bending the crank and with only minor marking of the surface. I'm primarily a function over form kind of guy, so I'm willing to live with it.











Before rounding off the bit above the crank pin.




After rounding off the crank pin, but off of the fixture for some reason.





And finally, setting up to mill a bit of piston skirt clearance (actually, to hide the marks from the crank web milling gouge, but don't tell anyone  )





And bead blast a bit of crap off of it, and the end result.


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## digiex-chris (Apr 1, 2015)

Some easy quick progress today, but hey, progress is progress. The crankshaft weight was hitting the liner, so I had to make a bit of clearance in the bottom of it. 0.045 off using the boring head and it cleared by 0.010. And an assembly of the parts just for fun.









Temporary mock-up bearings, I'll replace them with one that has a single rubber seal at the front.





Crankshaft and conrod through the rear hole





I should make another connecting rod anyway because it's ugly and easily visible. I haven't quite recovered from the span of time needed to feed 3 connecting rods to the scrap box monster yet though. Maybe next week. I've found a method that looks way easier than I was attempting.


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## digiex-chris (Apr 6, 2015)

I see how this goes. I'm making a theme of it for this engine. One part for the junk bin, one part for me ;D

Piston #1 is dimensionally perfect! Exactly to my standards, exactly the surface finish I wanted.

I turned the OD, filed and polished it to the correct size, test fit it into the liner, then pulled the chuck off and stuck it on my dividing head as a handy way to hold it, and drill/reamed the wrist pin hole. Then I clamped the chuck down on the table, and using the reamer, indicated it in parallel with the X axis. Then I milled the slot for the connecting rod. After trial fitting the connecting rod, I realized my error. The wrist pin hole is at the exact center of the piece, and at the exact right height, but 90 degrees off from where it should have been. I meant to cut the slot with the Y axis, but I'd used the X axis. Oops!





I'd only wasted an hour and a half with that attempt, I've certainly done worse. 20 minutes and I had another blank turned and ready to try again.

Piston #2 I realized that the horizontal/vertical nature of the mill provided a very handy possibility. I didn't need to indicate anything in except the piston concentric with the vertical spindle. Then I cut the slot first, returning to 0,0 with the DRO. Then I removed the vertical head, stuck the chuck in the horizontal spindle, found the piston skirt edge, moved the knee up to the right spot, and drilled/reamed the wrist pin hole, square to the connecting rod slot within the squareness of the mill.





Sweet! Though, before I took the chuck off the mill I should have cut the crank weight relief. You win some, you lose some. Happy with it overall.

The Trimble calculations tell me I want piston rings of 0.023" thickness. The junk box gods have smiled on me for once, and provided a hacksaw blade of exactly 0.023"! So I spent the weekend making a parting blade holder that takes hacksaw blades.


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## digiex-chris (Apr 7, 2015)

Here's my hacksaw blade holder









And a piston! 





The wrist pin is another shrink fit. I drilled the ends of it for brass pucks just in case the shrink fit temperature is exceeded during running and the wrist pin slips. I've ruined a two stroke liner with a wrist pin I thought was a secure press fit but it moved with heat.


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## Charles Lamont (Apr 8, 2015)

digiex-chris said:


> The wrist pin is another shrink fit.


What are the relevant dimensions (target and/or actual), and how will you assemble?
(My next job is gudgeon pin bores in pistons.)


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## digiex-chris (Apr 8, 2015)

Charles Lamont said:


> What are the relevant dimensions (target and/or actual), and how will you assemble?
> (My next job is gudgeon pin bores in pistons.)



I installed the pin just after that photo. It was kind of a feel thing rather than checking bore sizes, but I've worked with that size of fit in aluminium fairly often. I was working around the reamers that I had. The connecting rod bore was .251, the piston pin bore reamer was .249. I polished the pin until it fit with a tiny bit of slack in the connecting rod, but still didn't quite fit in the piston bore, so it was between .251 and .249, and measured .250 with a micrometer of unknown accuracy. I was targeting 0.001" over the bore size, and assuming it wouldn't just drop in once heated, and that I'd need to add a bit of force from a punch. I gave it a generous chamfer on both ends and center drilled both ends to take brass pieces. A light tap with a brass block felt like it would probably make it go in if I hit it harder but I wanted to be as sure as I could that I didn't upset any material that could work the hole looser later on and I didn't want to mar the finish on the piston. 

I polished about 1/8" of one end of it so that the end would fit into the piston pin bore without me having to hold a hot pin, hold the torch, hold the  hot connecting rod, and hold the hot piston while trying to tap it in, and also so that it would be less likely to raise and push aluminum ahead of it when I tried the next step. Then I went over to my bench vise, that had soft acetal jaws installed, and tried to push it in a little further using the vise. It was relatively easy to do, no threat of bending anything and not requiring excessive force, so I knew I was in the ballpark. The pin was installed about 1/4" of it's 0.8" length at that point. I could have pressed it in the whole way like this, but I was concerned about distorting the piston with the vise and then setting it into that distorted position by the force of the press fit. I thought that reducing clearance on the already tight slot was to be avoided at all costs so the connecting rod would be free to move. The original plan was a heat shrunk fit anyway, so I continued with that plan.

I clamped a low-precision v-block into the vise, one that I didn't care if it was heated up a little bit. I placed the piston into the v-block so the pin hole was vertical with the slightly-pressed-in pin pointing upwards, and the connecting rod hole aligned with the pin by looking through the opposite hole. The connecting rod bearing has a generous chamfer on it to help it self-align during this step.

Then I heated the piston with a plumbers propane torch until the part of the pin that was sitting in the piston began to show a light straw colour, and began tapping the pin down with a brass pin punch I had on hand. I didn't need a hammer or any other kind of striking tool, the weight of the 1/4x4" punch (with a tapered nose) by itself was enough. I kept tapping it down until it was just beginning to enter the connecting rod. Then I wiggled the rod to center it and free it up, then kept tapping and flipping it over by the connecting rod to check the progress until I was happy with it. I didn't need to re-apply heat, the job was over faster than I could type this.

One brass piece on the end of the wrist pin was a nice press fit and stayed in during the whole process, the other needed to be loctite'ed in, and popped out when I started heating it. I just reinstalled it with loctite when it was cool.

I'm glad I'd put an oil hole in the end of the connecting rod. The sides were such a close fit with the slot in the piston that I'm pretty sure next to no oil will get in that way. The second I splashed a bit of oil into the piston so it fell into the chamfered hole at the top of the rod, it all freed up nicely.


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## Charles Lamont (Apr 8, 2015)

Thanks for the write-up of your method. I think if I heat anything, and I probably won't, it will be the piston only.


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## digiex-chris (Apr 8, 2015)

The heat was likely overkill. With the slight taper on the tip 1/8", and finely polished, I think it would have been no problem to press it in. If it bound up the connecting rod I could have tapped it back the other way a bit to clear it. It was shocking how much of a reduction in required pressure there was though. Totally took the risk of breaking something with a hammer right out of the equation.


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## gus (Apr 8, 2015)

Hi Chris,
Wanted to DIY Saw Blade PArting Tool long time ago.Was procrastinating as I have never seen one working well.Thanks for the post. Will copycat. Beats re-inventing.

Have some regret using split pin to secure Rocker Arm/Clevis Pivot Pins and it does not look as good as using ''E'' Clips. Might just turn around and DIY same Parting Tool to cut Groove for ''E'' Clips. M.I.C. ''E'' Clips tend to open. Best to use M.I.J. Clips. Will beg/borrow/steal some from the fishing equipment shop.
Jerry Howell's V-2 prints called for ''E'' Clips and Gus deviated.


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## digiex-chris (Apr 8, 2015)

gus said:


> Hi Chris,
> Wanted to DIY Saw Blade PArting Tool long time ago.Was procrastinating as I have never seen one working well.Thanks for the post. Will copycat. Beats re-inventing.
> 
> Have some regret using split pin to secure Rocker Arm/Clevis Pivot Pins and it does look as good as using ''E'' Clips. Might just turn around and DIY same Parting Tool to cut Groove for ''E'' Clips. M.I.C. ''E'' Clips tend to open. Best to use M.I.J. Clips. Will beg/borrow/steal some from the fishing equipment shop.
> Jerry Howell's V-2 prints called for ''E'' Clips and Gus deviated.



Gus,

Forgive the messy drawing, but I measured up mine. Here's what I made (inch units). Absolutely none of these dimensions are critical, make it to whatever you've got on hand. Designed to fit a tool post that takes 3/8" tool bits, but I made no effort to make the hacksaw blade on-center with the lathe axis as I've got a quick change tool post. My junk box is full of 1/2" tall hacksaw blades. I had a dovetail cutter so I made the 60 degree angles in order to pull the blade into the vertical surface. (drawing attached).

Edit: just tap the clamp bolt holes before milling the relief on the bottom surface as the holes intersect the vertical portion of that relief. 

View attachment parting blade holder.pdf


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## gus (Apr 9, 2015)

Hi Chris,

Thanks. Drawing stored into ''' Tools to Make''.  In future ''E'' clips will be used to secure pivot pins. Now looking for good clips. The M.I.C. clips ''no can do'' as they have very poor holding power and tends to open up.


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## digiex-chris (May 27, 2015)

A few things have been delaying this project.

1) I needed to make some tools to radius the under side of the head
2) It's summer and I own a motorcycle

But I've made a little progress on a radius tool. I wanted to make it fit many types of jobs, so I needed a lot of adjustability and the ability to turn concave as well as convex radiuses. 

I got this idea from somewhere else on this forum, but I don't remember where. Apologies! In any case, I can't take credit for it, I only modified the idea for the bearing.





I didn't finish the whole top because it's some nasty very hard tractor parts that is cold rolled and warps like a banana. I did the top first, then flipped it over and cut some clearance on the bottom so I had 3 pads I could finish, instead of doing a finish cut over the whole surface. It worked well enough but my surface finish isn't great. It'll work fine. Pressed in a stud, pressed on a bearing, and had a wiggle-fit for the bearing into the under side of the tool arm holder. I loctite'd the block to the bearing.





1/2" slot 1/2" deep right down the center, and some clearance for set screws. This sets the radius of the curve. The slot is about 0.025" wider than 1/2", so when using 1/2" material, I could have a feeler gauge shim that the set screws would bite into, instead of biting into the arm and causing problems when trying to make tiny adjustments.





The tool bit holder arm in place. I brought it to the lathe, stuck a scriber in the spindle, and scratched where the tool bit would go, and drilled/reamed a 3/8" hole at that location. Then I drilled and tapped from the top, to insert a set screw. 

I just grind toolbits from broken 3/8" endmills. Flip the tool bit end for end to switch between concave and convex radii. The whole mess bolts down to the cross slide of my lathe with the compound removed.

Next I'll consider order of operations to make the head. Probably going to go something like this:


Bring a block to size, but about 3/4" taller than it needs to be. 
Hold it in the lathe 4 jaw, and turn the corners. 
Turn the concave under side. 
Remove from lathe, and bolt down to the mill table piston-side down, with the mill in horizontal mode. Indicating off of the table and the edge of the part, drill/ream the camshaft bearing locations.
Reinstall the vertical head, and drill/counterbore the head hold down bolt holes.
Remove the head and make a fixture that sits at the correct angle and has a register for the ring on the under side of the head, as well as 4 threaded holes.
Bolt the head to the fixture, and fly cut the angled top of the head (which will be located at the centerline of the camshaft holes).
While still in the fixture, mill the pockets for the valve train to fit inside, and drill/ream the valve guide and seat hole.
Flip the head 180 degrees and repeat on the other side.
Flip the head 90 degrees and complete the spark plug hole features.

The trickiest part is figuring out how to locate the features based on the edges of the tilted head block. I may have to get CAD involved so I can indicate off of known locations of the fixture instead.

Enough stuff to do that it may stretch throughout the summer months.


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