# Offenhauser Inline 4 cylinder, Might Midget Model Engine Build



## Eccentric (Feb 11, 2022)

I am starting a new build of the Offenhauser 97 Cubic Inch "Might Midget" Model Engine.  






The midget motorsports craze of the 1930s and 1940s not only served as a launch pad for many drivers who'd go on to successful racing careers, it also ended up keeping afloat one of the greatest companies in American motorsports history via the Offenhauser midget engine.

Not a year after Fred Offenhauser took over the operations of his former employer, engine builder Harry A. Miller -- which consisted mainly of casting, machining, and selling racing parts, and rebuilding truck engines -- a new business opportunity arose in the summer of 1934. Midget racing had taken the country by storm, offering cheap thrills for spectators and drivers alike in the depths of the Depression. Organizers soon capitalized on the new motorsport's popularity by building dedicated tracks around the country.

One of those promoters, Los Angeles-based Earl Gilmore, grew dismayed with the frequent breakdowns and the unruly nature of the miscellaneous motorcycle, junkyard, and cut-down engines that powered the cars racing at his stadium, so he turned to Offenhauser for help.

"(The unreliable engines) made it difficult to run a show," Gordon Eliot White wrote in Offenhauser: The Legendary Racing Engine and the Men Who Built It. "His patience exhausted, Gilmore sent his manager, David Koetzla, to see Fred Offenhauser about building a real racing engine for the little cars."

Offenhauser didn't have anything on hand at the moment, but he and Leo Goossen, the longtime draftsman for Miller's creations and their successors, pulled up the plans for the 183-cu.in. straight-eight that Miller built for Harry Hartz's 1932 Indianapolis 500-winning entry and decided to cut it in half to make a 97-cu.in. four-cylinder. As White described the engine's construction:
The 183 was, as Millers went, relatively simple, that is, inexpensive. It had two valves per cylinder and was unsupercharged. Using half of the 183's crankshaft left the midget engine with only three main bearings but it seemed to work alright."

In addition, Miller had designed the 183 as essentially two four-cylinder engines sharing a common crankcase so, White conjectured, "Offenhauser could use 183 blocks already on hand, or at least casting patterns for the Hartz engine."

With not much turnaround time, Offenhauser had the first midget engine ready in time for Curly Wetteroth to place it in his midget chassis and subsequently hand the completed car off to Curly Mills for its debut in late September 1934. Mills not only won that race, he also reportedly won his next 16 races.

Though the five total engines he built that first year seems like small potatoes, he charged about $1,100 per engine, roughly the equivalent of $20,000 today. "Fred had a healthy profit margin on them, and with the help of those midget sales, the firm cleared $18,000 for the year," White wrote. "They kept him in business."

Perhaps just as importantly, the midget engine sales -- White counted at least 180 during the time that Offenhauser ran the company -- allowed Offenhauser to develop the larger engines that would go on to dominate Indy and many other forms of motorsport for decades to come. 

When Offenhauser decided to retire shortly after the end of World War II, Louis Meyer and Dale Drake bought out his business in 1946 and continued offering the midget engine until about 1974. While it didn't sell in great numbers -- White recorded serial numbers up to 450 or so -- it remained popular and powerful enough to warrant continued development through the decades. Meyer and Drake, in fact, sold most of their midget engines as 102-cu.in. variants and even offered the engine in displacements as large as 111 cubic inches.
---------------------------------------
I have created a 3D Model of the early 97-cu.in. version and am working on a set of plans for this historic engine.





I am building what is really a prototype of a never before built model.  I am starting as is tradition with the crankcase.  The crankcase is split into two halves held together with 4-40 screws hidden behind the crankcase side covers.
I started by squaring up the two work pieces in the mill, then moved them to the CNC router to machine the insides.  I also machined what I am calling a "dummy crankshaft".  It will allow me to check the bores in the crankcase.  The crankshaft is supported at the ends by a pair of ball bearings and in the center by a bronze bush. Its fabrication was a straight forward set of operations on the lathe.  I slowly brought the ball bearing surfaces to dimension to insure a tight fit. The front end of the crankshaft will hold the timing pinion and a starter dog.  The rear end of the crankshaft will hold the flywheel.





Below is a photo of the top and bottom crankcase halves with the internal machining complete.





The crankcase is about 4 1/2 inches long and 2 inches wide.  If you look closely you can see that the top left and bottom right screw holes have a locating hollow pin surounding the mounting screw that perfectly aligns the two crankcase halves.  All of the machining on the inside, including the ball bearing holder surfaces and the locating pins, were performed in one setup.  The machining time for the crankcase top was 1 hour and 32 minutes while the machining time for the bottom half was just under 2 hours.





When I machined the bottom crankcase half, I took an extra .010" off the top surface to allow for a Teflon (PTFE sheet) gasket.   I then assembled the two halves with this gasket material in place.  The rest of the crankcase outside machining will be  performed with the two halves screwed together like this.










I plan to machine the front and rear of the crankcase next so I can test fit the dummy crankshaft.  I may leave the machining of the sides and bottom of the crankcase for later as it will be easier to work with as a solid block.


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## propclock (Feb 11, 2022)

Thank You


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## stevehuckss396 (Feb 12, 2022)

Awesome start to something that is interesting as heck to me. I will be here the whole way!


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## Vietti (Feb 12, 2022)

Any idea what kind of horse power these engines made??  

Will be looking forward to progress!  
Thanks for taking the time to show your work.

John


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## CFLBob (Feb 12, 2022)

I just want to know how you tighten those cap screws.  I could see how you could get an Allan wrench in there, but it looks like you could barely rotate it.  Maybe 1/20 of a turn at a time.  It would take an hour to tighten those 10.


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## Eccentric (Feb 12, 2022)

CFLBob said:


> I just want to know how you tighten those cap screws.  I could see how you could get an Allan wrench in there, but it looks like you could barely rotate it.  Maybe 1/20 of a turn at a time.  It would take an hour to tighten those 10.



A ball end Allen wrench easily tightens them.  But you are right, a normal Allen wrench would never work.


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## Eccentric (Feb 12, 2022)

Vietti said:


> Any idea what kind of horse power these engines made??
> 
> Will be looking forward to progress!
> Thanks for taking the time to show your work.
> ...


The early engines turned out about 100Hp,  but as the design was refined the engine was producing 120 HP at 6000 RPM running on alcohol in 1947.  By the 1950s, the 102 cubic inch Offy midget was producing 132 HP with carburators, and 143 HP at 8000 RPM with fuel ingection.


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## Eccentric (Feb 12, 2022)

Machining the Front of the Crankcase
Machining the features at the front of the crankcase requires precision because three gears and their bearings are mounted here.  For the gears to mesh correctly they need to be precisely spaced from each other.  The position of the front crankshaft bearing holder has already been machined and all of the features on the front need to be precisely placed with respect to it.  
Below is an image of the front of the crankcase and it can be seen that there is a lot going on there.





Before starting the machining I go to the surface plate and carefully characterized all of the dimension of the assembled crankcase, using the center crankshaft hole as my master datum.  I created a detailed sketch with the dimensions of the actual part, the actual size of the crankshaft bearing holder hole and its relation to all sides of the part.
Then the crankcase is mounted in the vise vertically and squared to the axis of the CNC router.  I spent an afternoon checking and rechecking the alignment and touching off the part aligning it to all of the axis of the CNC router.  I used the dimensioned sketch to check the alignment several ways using them to double check each other.  Then I slept on it.
The next morning I rechecked the centering of the crankcase in the CNC vise, then ran the set of programs machining the front.  The machining on the front took 25 minutes and the machining of the holes took another 8.






Below is a picture of the CAD model and the resulting machining of the front of the crankcase.  One of the small bearing has been test fit.  There is a second bearing not installed equidistant below the crankshaft.





Then I machined the two crankshaft main bearing holders, one is mounted on the front of the crankcase and another on the rear.  Below I am test fitting the crankshaft ball bearing for a nice snug fit.





Then I turn the features on the outside of the bearing holder and test fit it into the crankcase, again to a nice snug fit.





Below are a couple of pictures with the dummy crankshaft installed in the engine with the two main bearing holders supporting it.











I heave a sigh of relief.  The most critical features of the crankcase have been completed and I am satisfied with the precision of alignment on the different sides.


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## mayhugh1 (Feb 14, 2022)

Eccentric said:


> A ball end Allen wrench easily tightens them.  But you are right, a normal Allen wrench would never work.


I'm wondering how you'll tighten the rod caps during final assembly. I used the stock side access openings for access to the rods' big ends, and so I made sure the openings were wide enough and lined up with the locations of the rod journals. Make sure you've given thought as to how you'll assemble the ring'd pistons into their cylinders and onto their rods and the rods onto the crankshaft. - Terry


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## Eccentric (Feb 14, 2022)

mayhugh1 said:


> I'm wondering how you'll tighten the rod caps during final assembly. I used the stock side access openings for access to the rods' big ends, and so I made sure the openings were wide enough and lined up with the locations of the rod journals. Make sure you've given thought as to how you'll assemble the ring'd pistons into their cylinders and onto their rods and the rods onto the crankshaft. - Terry



Terry,

My engine is simpler than your Offy.  You had your crankshaft running on 5 bearings, three bronze bushings between each of the four cylinders, 2 ball bearings pressed into each end of the crankcase, and another in the front cover.  Your bronze bushings were mounted to the crankcase bottom half.  Once you installed the crankshaft into these bronze bushings, it is difficult to access the rod cap screws.  Thus the access through the ports in the side of the crankcase.  That is the way the real Offy is assembled, by the way, through those side access ports (I can't imagine).

I am using three crankshaft  bearings, 2 ball bearings in ball bearing holders at each end of the crankcase and a single bronze bushing in the middle of the crankshaft.  My split bronze bushing is secured with a bearing cap screwed to the crankcase top half. Since the crankshaft is secured to the top crankcase half, I will have access to the rod caps. My crankcase bottom half is like a sump and will be installed after the connecting rod caps are secured.

Below is an image of the engine upside down showing these features. (the center bronze bush is missing from the model)






Thanks for the guidance, I have designed things in that past that have not been manufactuarable for the very reason you state, "how the heck am I supposed to get a tool in here?" or "how is this parts supposed to slide past that part?" That is why I am classifying this as a "prototype" build, there is a good chance I will have to scrap and redesign parts before I am through.  I appreciate your eagle eye.

Regards to an earlier comment of yours "to not forget about the gaskets", per your suggestion, I have gone back and actually included the gaskets in the 3D model as parts.  In the image above one cylinder sleeve is removed and I have pointed to the .020" thick head gasket.   I decided not to leave it to the fabrication step to make the allowance for the gaskets.

Thanks for your attention,

Greg


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## mayhugh1 (Feb 14, 2022)

Thanks. I missed that. Good work. - Terry


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## Eccentric (Feb 16, 2022)

Front Cover -

The front cover seals the front of the crankcase and houses the oil pump and three gears, the crankshaft pinion, the oil pump gear and the valve timing drive gear.  The features in the front cover hold two ball bearings for the gears need to precisely align with their partner bearings on the front of the crankcase. 






Machining the front cover has several challenges, the foremost is aligning features on both the front and back sides.  A secondary challenge is the tight quarters and fine details on the front face of the cover. The mating surface of the crankcase was machined in one setup, so the bearing holding features and the mounting holes for the front cover are well aligned.  I will do the same on the front cover, machine the bearing features and the mounting holes in the back in one set up.  Then I will load a piece of fixture stock in the mill, and machine holes matching the eight mounting screw holes in the front cover.  I will then screw the front cover front side up with four of the screws, and machine as much as I can. Then I will put in the other four screw, remove the first set of four screws, and machine the balance of the front cover.

Below, the inside of the front cover is being machined.  This is a straight forward set of operations because they are essentially a copy of the set performed on the front of the crankcase.





Below is an image of the finished inside machining.





I then use a band saw to remove most of the material on the front side of the cover, following up on the mill to provide an accurate surface to start with on the CNC router.





A fixture block is loaded into the CNC router vise.  I perform a finishing operation  on the top to flatten it and provide a known surface with respect to the CNC Z axis.  Then the six mounting holes are machined and tapped.  One of the holes was used as the X and Y axis zero set points and the top surface becomes the Z axis zero set point.  





Below the roughing pass begins





I used a 1/4 flat end mill for initial roughing and machining of the horizontal flat surfaces.  Then I used a 3/16ths ball end mill to machine the curved outer surfaces, and finally a 1/8 inch ball end mill to create the fillets around all of the features.  I either used a dull 1/8th inch ball end mill, or did not properly match the spindle speed with the surface speed, but I was disappointed in the finish of the radius operation. Oh, and I hit the screw holes with a 3/16th flat end mill to create the counter sinks.





Below is the front cover mounted on the front of the engine.


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## e.picler (Feb 17, 2022)

Very nice work Greg. Congratulations!
This engine is a real challenge.

Tks,
Edi


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## Eccentric (Feb 19, 2022)

*Cylinder Block*

The cylinder block forms the water jacket around the cylinder sleeves.  It is a block of aluminum with most of the material machined away, then a lot of holes are drilled in addition to the bores for the cylinder sleeves.  There are two side covers that mount to the sides of the block sealing the water jacket.

The block is shown in blue in the image below:





It was going to take two hours on the CNC Router to machine out all of the aluminum from the inside of the block, so I decided to use a drill bit and an end mill on the manual mill.  I started by drilling 1/4" pilot holes, then followed up with a 7/16th drill bit to remove the majority of the material.  Then an end mill squared up the pocket.  Finally I hit the corners on both sides with a 1/16th end mill for the small radii needed there to clear some screw heads.





On the CNC router, I machined as much as I could from the top of the block including the cylinder sleeve bores, then drilled the few holes on the bottom of the block by hand.  I made the block with an extra .010" of material on one side for some reason, and then touched off the bottom holes and the top holes on different sides of the block by accident.  So the holes on the bottom are offset to one side by .010"  Fortunately I have not drilled the matching holes in the crankcase and can offset them by the same amount and no harm no foul.

An interesting feature of the Offy block is the taper in the sides.  Instead of machining a custom fixture I simply clamped the block in the mill vise with a spacer so I could machine off the required .065" from the bottom of the block and taper it to 0.0" at the top.  I used an indicator to insure my clamping was correct.





Then I ran an end mill around the edge.





Below the block sits on the crankcase in its intended position:





The block weighs just a wiff of what the squared up work piece did.  I still have to drill and tap *64 holes *for the 0-80 screws that secure the  side covers.  I will machine and drill the side covers, then match drill the holes in the block to insure good alignment. The side covers need to be flush with all sides of the block.


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## Basil (Feb 20, 2022)

Your making amazing progress. As a matter of interest what CNC router do you have? I just took delivery of a Onefinity. I really have missed my larger CNC and I'm hoping this will fill the void a bit. Looks good so far.


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## Eccentric (Feb 20, 2022)

Basil said:


> As a matter of interest what CNC router do you have?



I originally built a CNC router using a Dewalt Router motor to machine wood for madolins and gutairs. It is a gantry type and I copied a few designs I found on the internet. It worked really well and I enjoyed it for the complexity of projects I could tackle. I used a PC along with PC power supplies for each axis. The software consisted of a DOS program called TurboCNC and VisualMill to create the tool paths.  I did invest in good linear slides and ball screws, but the rest of the machine was build out of MDF--not real rigid, but accurate if light cuts are taken.

 Later, I rebuilt the Z axis and upgraded the spindle to a water cooled variety designed for machining metal.  Also I went to hybrid stepper motors from Leadshine (can not say enough great things about them) and moved to LinuxCNC.   The machine now does a good job with aluminum and can handle steel if I take small cuts.  A 1/4" end mill is the largest I can reasonably use, if I go larger you can see artifacts in the machining due to vibration and resonances of the machine and there is no real advantage.  As with any milling machine, I wish I had more Zed height, I only have a few inches.

I am wary to recommend CNC to my machinist friends becasue of the amount of computer work that is required.  I come from an engineering background and I enjoy working on the computer, designing parts and creating tool paths. Creating a one off part on a CNC requires much more time sitting in front of a computer than in the workshop.   That is one thing I like about model engine building, there is a variety of machining skills required;  the CNC can help, but I still spend more time at the lathe and mill than the CNC router.

Since you come from a CNC background and know what you are getting into, I am sure you will enjoy the Onefinity CNC.


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## Eccentric (Feb 21, 2022)

Cylinder Head

The cylinder head is one of the most complex parts in the engine.  It has coolant passages, oil passages, not to mention the intake and exhaust ports.  The camboxes mount to the head and so its dimensions dictate how well the timing gears mesh.






I start with machining the internal features including the coolant passages and the coolant cavities.  The coolant passages connect the coolant water pipe flanges with the internal coolant cavities.  The coolant passages are drilled the long way through the head, they are .150" in diameter, so drilling the 2" from both ends to meet in the middle is relatively easy. 





The coolant cavities are machined into the head with a 1/4" roughing end mill.




Three small matching cavities covers are made from 1/8" aluminum sheet.





The caps are secured in place with high temperature structural adhesive. 






I set the adhesive aside to cure for a day and then fly cut the head top to final dimension.






I am happy with the way the sealed coolant cavities turned out. No one will know about them but us.





I drill the four spark plug holes.





Then I begin machining the bottom of the head.






Once the conical combustion changers are machined on the CNC router, it is back to the manual mill to spot drill, drill and tap the holes on the bottom side of the head.





Oppps ...... I hit my picture limit, the rest of the post can be found here:
Offy Cylinder Head


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## Eccentric (Feb 24, 2022)

Cylinder Head - Part 2

In this second installment describing the machining of the head, I show the steps to machine the two non-vertical/horizontal surfaces--the face the intake and exhaust manifolds mount to, and the face the cambox mounts to.

First I use the CNC router to machine the two bevel surfaces on each side.  Why not use the router to complete the machining on these beveled sides?  I couldn't, given the limitations of my little CNC router.  The work piece is 4.125" long and the vise on the CNC router can only open to 4".  My mill vise is larger, but I can't use it on the CNC router because it is too tall and I don't have enough Zed clearance. I reasoned that this part needs to be clamped from the ends since these are the only two vertical surfaces the vise can bear against.  I looked at a couple of fixtures, but the rotational forces of clamping the part would result in an unreliable work holding situation.

I can probably manual mill the features faster anyway.  I decide to start with the simpler face first, the manifold mounting surfaces.  The four port holes were machined in an earlier step, so already exist.  There are only the 7 threaded holes for mounting the exhaust/intake manifolds and the 4 holes for the pins securing the valve cages.  These are shown below.







I have been creating the drawings for the parts as I build and machine them; this way I can find issues with the print.  I find a couple of missing dimensions and hole callouts.







There is a fixture required to align the beveled surface I am working on.  I decide to 3D print it.  the fixture carries light loads during the milling operation and no clamping force.  Designing and printing the fixture part is much quicker than using a piece of aluminum for a one off fixture.







I do not rely on the plastic fixture alone.  An indicator is used to verify and tweak the clamping to insure the surface is properly aligned with the mill table. You can see that a sheet of notebook paper was used as a shim to bring the part in perfect alignment.  I use a square to confirm perpendicularity and an aluminum rod on the moveable vise jaw to insure only the primary face of the vise jaw is aligning the part.

As mentioned before the four large port holes were drilled in an earlier operation.







Once the part is secure in the vise and aligned to the mill, spot drilling, drilling and tapping the holes is routine.







Machining the cambox face is more complex because in addition to drilling and tapping holes, I need to drill and ream the large holes for the valve cages, then machine the oil collection channel.







All of the machining on the head prior to today's operations used the center of the part as the origin.  This way any variation in the outside dimensions of the part will be spread evenly on all sides.  If you look at the print in the picture above, you can see all the dimensions are referenced to edges.  This could result in slight miss alignment as tolerances would be biased to one side.  I realized this before I machined the Cambox surface and created the print using the center of the surface as the datum.  I doesn't really matter what is used as a datum as long as the machining operation on all of the faces use the same ones.

Below I spot drill the four holes for the valve cages.






The rest of the post can be found here:
Offy Cylinder Head - part 2


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## Carbuilder (Feb 24, 2022)

Eccentric said:


> I am wary to recommend CNC to my machinist friends becasue of the amount of computer work that is required.  I come from an engineering background and I enjoy working on the computer, designing parts and creating tool paths. Creating a one off part on a CNC requires much more time sitting in front of a computer than in the workshop.  That is one thing I like about model engine building, there is a variety of machining skills required;  the CNC can help, but I still spend more time at the lathe and mill than the CNC router.



This is excellent CNC advice for someone thinking of getting into it. When you see pictures/video of a CNC cutting parts you think what a great time saver it will be. As you say, if you enjoy computer work then it is fun. If you think you are going to be able to make parts a lot easier then....well....maybe. There is something fascinating about watching the CNC cut a part. Buy you will spend a lot of time on the computer before you make it into the shop and you will be very frustrated when you spend all that time and then break a cutter the first time it hits the block of metal.

But I am a real fan of CNC. Sometimes a break from the shop and onto the computer is a good thing.

Your work is very impressive and I really like this engine.

Rick


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## Basil (Feb 25, 2022)

Eccentric said:


> I originally built a CNC router using a Dewalt Router motor to machine wood for madolins and gutairs. It is a gantry type and I copied a few designs I found on the internet. It worked really well and I enjoyed it for the complexity of projects I could tackle. I used a PC along with PC power supplies for each axis. The software consisted of a DOS program called TurboCNC and VisualMill to create the tool paths.  I did invest in good linear slides and ball screws, but the rest of the machine was build out of MDF--not real rigid, but accurate if light cuts are taken.
> 
> Later, I rebuilt the Z axis and upgraded the spindle to a water cooled variety designed for machining metal.  Also I went to hybrid stepper motors from Leadshine (can not say enough great things about them) and moved to LinuxCNC.   The machine now does a good job with aluminum and can handle steel if I take small cuts.  A 1/4" end mill is the largest I can reasonably use, if I go larger you can see artifacts in the machining due to vibration and resonances of the machine and there is no real advantage.  As with any milling machine, I wish I had more Zed height, I only have a few inches.
> 
> ...


Cheers Greg, Thank you so much for the info. I now have the Onefinity up and running. At the moment I am getting to grips with Fusion CAM. I've been looking to get a small CNC for a while now and the Onefinity looked like a very rigid setup. 
I just could not get my head around machining some of the complex shapes on my little Honda project that I wanted to look like stock castings.


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## Eccentric (Mar 3, 2022)

The timing gear tower houses the majority of the timing gears and is mounted on the front of the engine as shown below.






The timing tower assembly consists of a front and rear half, each holding 6 ball bearings for the gear shafts. The quality of the gear mesh is determined by the alignment and precision of the gear tower inside machining which includes not only the bearing positions, but the alignment of the screws holding the assembly together.  For this reason, all of the inside machining of both halves was done first and done in a single set up.   There is a fair amount of machining required on the outside face of the timing gear tower front half.  This was done as a secondary operation with the work piece mounted on a fixture using the screws for alignment.





Inside Detail of the timing gear tower assembly


I start with the inside of the rear timing tower first as the back of the part is flat with minimal machining.  Then I perform basically the same machining on the inside of the front timing tower.





Once the machining is complete on the inside of the rear gear tower, I secure it face up on a fixture block that has been prepared by machining it flat and the screw holes drilled and tapped. 





Since I needed to machine the complete front face of the gear tower, I had to machine in two separate operations because the securing screws were in the way.  I secured the part to the fixture with four screws as shown in the photo, machined half, then moved the mounting screws to the area just machined and completed the secondary operation.





I had an error in my tool path and I crashed the end mill into the part, this resulted in a blemish on the face of the finished piece.


Machining of the face was accomplished with a 1/4" end mill, a 3/16" ball end mill and a 1/8" ball end mill.





Likewise when I machined the countersinks for the mounting screws, I had to move the screws around so the work piece remained firmly mounted.





Below is an inside view of the two gear tower halves.





A closeup of the gear tower




I will finish the part with bead blasting and then hand sanding to give it a used cast aluminum look, like I did on the front cover.  When asked about the blemish, I explain that I machined a Carnation flower into the face as a sort of makers mark.


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## stanstocker (Mar 4, 2022)

The carnation adds a fine and regal look to the engine.  I can't imagine the level of effort and commitment required to add such a fine flourish to an already very high level effort.  Those of us who have a history of decorative embellishment salute you!

Cheers,
Stan


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## Eccentric (Mar 16, 2022)

*Offy - Block Side Plates/Crankcase Sides*
Machining the sides of the crankcase was straight forward, but a little nerve wracking as the number of hours invested has grown and the anxiety of messing up has increased proportionately.  Below the crankcase is being rough machined.  The crankcase is assembled with the dummy crankshaft, bearings and most importantly the crankcase gaskets.
Notice how the crankcase is mounted in the vise.  The datums being used are the top of the crankcase flat against the primary vise jaw, the forward face of the crankcase covered in layout fluid, and the opposite side of the crankcase mounted down flat against the vise.  An aluminum round is used to press the crankcase top against the primary vise jaw to insure this datum is in alignment with the mill.






Below the  ball end mill has completed the finish milling of the crankcase side and an 1/16" end mill is being used to "drill" the holes for the crankcase breather plate mounting holes.






There are two cylinder block covers that mount to both sides of the block.  The one on the left side is simply a flat finned plate, but the one on the right has a small water jacket pocket and the fitting for the water flange.  After machining the features on the surface, I spot drill the mounting holes.  I have not had good luck actually drilling holes on my small CNC router, there is not enough Z height to get a drill chuck mounted.  I kludged one up using a standard drill chuck in a collet, but the run out was atrocious.   So, for small holes I spot drill, then final drill on the mill, or for larger holes I will simply mill them out with an end mill. 






The block side plates are held in place with a large number of 0-80 socket head cap screws, I drill the .070" holes with the side plate mounted in its final position on the block in the mill vise.  That is, I match drill the holes in the side plates and the block at the same time.  I had to be sure to install the .020" head gasket and the .010" block to crankcase gasket to insure the spacing was correct.  I tap the holes in the block and I drill out the holes in the side plates to a .089" clearance size.












Above is a picture of the engine as it stands now.


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## petertha (Mar 17, 2022)

Very nice work. Your pace is amazing.


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## Eccentric (Mar 22, 2022)

*Offy - Crankshaft*
Time for the crankshaft.  I start by stress relieving the steel in the heat treat oven.  I heat it to 1150 degrees for two hours, then let it furnace cool over night.






Notice in the image below that the compound has been replaced by a simple steel plate.  The compound is the least rigid element in my bench top lathe and replacing it with this plate really helps the surface finish quality.






I remove most of the material on the mill, chain drilling and edge milling.












When machining a crankshaft by turning it on centers, there is a fair amount of force created by the tail stock holding the work piece between centers.  This is important as it registers the crankshaft to the center and the live center for repeatable concentric machining. I have found that the spacers used to transfer this force between the crank webs must be accurately machined to be a close fit.  Too tight and the spacers actually open up the webs while the crank is machined, which springs back once the spacers are removed.  Too loose and the opposite happens--in either case the machined journals are not co-linear with each other. Also, the interrupted cut can tweak the crankshaft as well, so small cuts are in order, even when roughing out the crankshaft.  The spacers shown below are custom machined on the mill for each crank web and are labeled so they can be returned to the correct position.

The ball bearing can be seen test fit on its main end journal.






Below I am test fitting the crankshaft in the crankcase.  The red Dykem is used to highlight any areas of interference.






Below is the crankshaft with the major lathe work completed.  It is next to the dummy crnakshaft I have been using up to this point.






Below I am drilling the lightning holes through the center of the rod journals.  These will have their ends caped and be part of the internal crankshaft oil system.






Below is a cross section of the crankshaft showing how oil is delivered to the connecting rod big ends.  Oil is delivered to the center crankshaft main bushing under pressure. Again, note that the ends of the big lightning holes through the conrod big end journals will be capped at each end.






To drill the diagonal oil gallery, the starting position of the hole is spot drill with the crankshaft horizontal at the specified point. 






Then the crankshaft is held at the specific angle and the beginning of the hole is spot drilled again.  Finally, the hole is drilled through.






Then I machine the keyway for the timing gear placed at TDC for cylinder #1. Indicated by the red arrow.












The crankshaft is in good enough condition to allow the test assembly of the rest of the engine. It turns true on the main bearings and I am happy with the runout of the center main journal. At some point I will need to clean the crank really well and cap the large lightning holes.


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## Ghosty (Mar 22, 2022)

*Eccentric*
I normally glue the spacer piece in and leave it until all machining of crank is finished, that way you will not accidently build in any warp or twist.
Cheers
Andrew


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## petertha (Mar 22, 2022)

Enjoying your build @Eccentric 
Can you elaborate on how you were validating the CS with the red dykem in the crank case? For example if it did bow in stress releif, then you would be expecting some rub on the ends of the throws? (So that means the line bore is very close to the swing diameter?).

Did you employ any special lapping tools for the journals, or just careful hand work?


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## Eccentric (Mar 24, 2022)

Peter,

when I first installed the crankshaft in the crankcase there was a little interference as I turned it.  I used Dykem to see where this interference was.  It turned out that the corners of the crankcase are radiused and I did not relieve the corners of the crankshaft enough to clear.  A small touchup of these corners on the crankshaft and all was well.


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## Eccentric (Mar 24, 2022)

*Offy - First Gear*
The Offy has a lot of gears in the timing gear train and I want to have the gear tower populated before I fabricate the camboxes to insure I have the proper gear mesh between the gears in the gear tower and the camshaft gears.  This sequence is how I make gears. 
I make a sacrificial gear arbor in the lathe, putting grooves as shown for the super glue to seep into.






I cut the blank from the mother material, in this case brass, center punch the center.  I super glue the blank to the arbor, using a live center in the tail stock to center and put pressure on the glue joint. 






Once the super glue is cured, I drill the shaft hole under size and ream to the shaft diameter, in this case 5mm.






I don't completely trust super glue in this application so I also use a screw, not to center but to secure.  So I drill and tap for a 10-32 screw.






I turn the blank OD down to size.  In this case we are making a 54 tooth .5 Module gear with an OD of 28mm.
The CNC is used to cut the teeth.  If anyone is interested, I can provide the Gcode file to do this, it is quite simple.






After the teeth are cut, I turn the gear again on the lathe bringing the OD back down to the proper size.  The gear cutter throws up burrs that are removed in this way.  The gear is faced and the .5mm X 7mm spigot is machined.






I heat the gear and pop it off of the arbor. The arbor is refaced and a pocket is machined to match the spigot.






The gear is again super glued into place using the spigot and tail stock to align the gear to the center of the lathe.






Again a screw is used to secure the gear to the arbor and the gear is turned down to final thickness.  The screw is removed and the spigot is carefully turned down, I remove .005" of material at a time so I don't bust the super glue joint.






I lightly touch the teeth edges with a file to remove burrs created from the facing operation, but not much, I want to maximize the tooth engagement surface area.  Finally I clean up the teeth with a piece of folded 600 grit sandpaper to clear the last of the burrs from the teeth.


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## gbritnell (Mar 25, 2022)

Great work! I really like all the documentation and I know how much extra work it takes to do it. Thanks
gbritnell


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## mayhugh1 (Mar 25, 2022)

Really nice work and I also appreciate the effort put into documenting it.

Something to think about before you get too far into brass gears. There's a lot of stress on the tiny teeth of those gears in that gear tower stack. I machined my gears from Stressproof. Ron Colona in fact had one of his 12L14 gears fail, and the broken tooth damaged some other gears in the tower. Of course, he likes to rev his Offy up to 10krpm. I'm not that brave. Ron then switched to Stressproof as well. - Terry


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## Eccentric (Mar 25, 2022)

Thanks for the kind words George and Terry, and the advice.  I have ordered a 1 foot, 1.25" round of 1144 and it will be here on April 6th.  There are plenty of other things I can be working on until then.  I have not worked with 1144 before and this will be a good opportunity to see what machining it is like.

I have made a few more brass gears and I am working on a depthening fixture for them.  I want to make sure I have my numbers dialed in, particularly the infeed distance of the gear cutter.  Brass I cut in one go, but I understand steel needs to be cut in several increasingly deep cuts to extend the life of the cutter.  Surface speeds are more critical as well.

Greg


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## Eccentric (Mar 31, 2022)

*Offy – Cylinder Sleeves*

The sleeves are made of cast iron and I start by removing a lot of the material on the OD, but do not bring it to final dimension.  I drill most of the material from the bore by stepping up in drill sized until I am a 1/16″ from final dimension.




The techniques I used to get a good finished ID included the following:

Used a four jaw chuck to give max clamping support on the blank cast iron work piece.
Bring ID to size before the OD to provide more material to stabilize the blank while cutting the ID.
I used an oiled stick and applied constant, but slight, pressure on the outside of the sleeve, sort of a poor man’s following rest to counter act the pressure of the boring tool. Without this I was getting about .002″ spring in the part from the start of the boring pass to the finish.  See below.
Replaced the compound with a simple steel plate to make the carriage as ridged as possible.
Position the Tool post to maximize the engagement of the cross slide gibs.
When close to my final dimension, I used several spring passes where I do not advance the cross slide, just ran again and again
I ran the lathe really slow so there was no chatter, I had to go down to 280 RPM, but got really clean cuts.
I used the finest power feed setting. A single pass took about 6 minutes





As can be seen below I have achieved a very nice bore finish on the inside bore.




I have learned the hard way that when building a multiple cylinder engine, all of the sleeves need to have the same internal bore diameter so you only need to make one size and therefore one batch of rings.
Below I am brining the OD down to size and test fitting them in the block as I go.




Then insure the OD also fits nicely into the crankcase.




My idea was to make a barrel hone from a section of 3/4″ aluminum rod.  Turn the outside, drill and tap a hole down the middle and then split it with a saw.  A taper bolt is then fabricated to provide the adjustment  of the taper.
But it turned out that I put a slight taper on the aluminum rod and then used it to hone the cylinders to the same size.  It was slow work, but they all came out with the same ID and nice surface finish.
Below is how I held the cylinder as I used the lathe (at the slowest speed) to turn the barrel hone. 
I used 300 and 600 gm diamond paste mixed with WD40 as my polishing compound. I did get one sleeve stuck and had to take the hone assembly over to the vise and tap the hone out.




The following series of photos show the diameter of the hone and the position the cylinder will slide over it, both bottom first and top first.  The taper is such that the bottom of the sleeve is slightly larger than at the top.







bottom first, the sleeves slide up to the finished point on the hone.




Below, top first and the sleeve will not slide very far because of the taper in the sleeve.




The majority of my cast iron rod is reduced to chips.




Above the cylinder bock with the completed sleeves can be seen.
Cast iron is messy to work with, so upon completion of the sleeves, the lathe needed a good cleaning and oiling.  I use Vactra Oil No. 2 for ways oil.


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## Eccentric (Apr 7, 2022)

*Offy – Crankcase Breathers*

One of the most distinctive features of the Offy is its crankcase side breathers. These are highlighted in the photos below.





On the early engines these were quite low, over time they were raised and additional internal baffling was added.





Only the right side of the engine has these breathers so I start out making the left side since it is simpler.  A 1/8″ ball end mill is used for the final finishing of the fins.





Below is the roughing pass on the right side breather plate.  I left too much material on the original work piece.  A tool caught it on the finishing pass and snapped, a little bit scary.  The finishing tool path wasn’t aware of the big chuck of material and made an approach through it.  I  did not include the oversized work piece in my tool path simulation, otherwise I would have identified the issue before the run.  Fortunately the part was not ruined, just the end mill and my pride.





Below is the finishing pass, again with the 1/8″ ball end mill running a .007″ stepover.   The finishing pass took about an hour.







Then it is on to the breathers themselves, below is the roughing pass on the bottom of the part.  I have used 2 flute end files for ever on my CNC router, but recently I have switched to three flute end mills and have been pleasantly surprised how well they work.






Below is the finishing pass on the top side of the breathers.






the breathers are mounted in the crankcase side plates at a 10 degree angle.  I made a set of custom angle fixtures with the 3D printer.  On a small part as this with very light cutting forces, they work really well and are quick and easy to gen up.





The machining was done on the  manual mill.






I went for a tight press fit.  There will be a set screw coming in from behind the cover plate to secure the breathers.  Below is a test fit.






Then the other side.






Below is the finished part along side the 3D printed fixtures.






The crankcase side breathers installed on the engine.  I think they look cool.





There are a couple of additional holes to be drilled to make the breathers functional, and like the originals I am sure they will leak oil.  Maybe install a PCV in them?


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## stevehuckss396 (Apr 7, 2022)

Looks about right to me. Nice job!


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## propclock (Apr 7, 2022)

Beautiful. I recommend you always put a size reference
object  in your  photos. That small scale is amazing to me. 
Your detail looks like it could be a much larger scale.
Thank you for the excellent posts. 
 Again I am amazed and impressed.


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## gbritnell (Apr 8, 2022)

Fantastic work! Are the breather caps going to be functional?  I would recommend having some kind of breather or it will smoke from too much crankcase pressure.


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## Basil (Apr 8, 2022)

Beautiful work Greg! You really are moving along with it.


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## n1326e (Apr 9, 2022)

Anyone interested in these type engines, there is an excellent multipart interview, on youtube, with Prof. Steve Truchan. It covers bits and pieces of the history of Miller, Offenhouser and Myer Drake. Prof. Truchan overhauls and restores these engines, old Indy cars,etc. 
Here's the link:   

Tom Warren


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## Eccentric (Apr 22, 2022)

*Offy – Camshafts*
The Offy has two overhead camshafts, here I will machine the exhaust cam shaft. The intake camshaft will follow the same process, but with a different cam lobe profile.




Cam Blank diameter  .430″
Cam Base Circle Diameter  .25″
Nose Radius  .025″
Lift  .090″
Flank Diameter . 743″
Lift Duration 128 degrees
Max Lift Occurs: 235 degrees after TDC

I start with a 5″ length of 7/16″ drill rod and drill a 1/16th inch hole all the way through for the oil feed.  I drill from both ends and meet in the center.  I start with a shorter drill bit and peck drill, drill a crank or two on the tail stock, retract, clear the chips and repeat.  I then use a longer drill bit as shown below.  I do not drive the drill bit, it is a very light touch where I am letting the drill do the work and I take up the slack with the tail stock handle.





Then I machine a flat on the cam shaft blank, this is used to register the lobes as shown below.





Below I use a level sitting on the flat to establish zero degrees on the rotary A axis.





Then I machine one lobe at a time, sticking out as little as possible for each lobe.
the flat can be seen below.





And the lobe taking shape is below:





When machining of the lobe is complete, I pull a length of stock from the collet, reestablish the zero point on the rotary axis, then turn to the rotary position of the next lobe, reset the zero point on the rotary axis.  And run the lobe cutting program again.





Below is the camshaft blank with the four exhaust lobes machined.





Then we move over to the lathe and turn the rest of the features.





Below is the print and dimensions used for first section of the cam shaft, the section shown above.





Below I am drilling four holes in the cam shaft that will be used to register the cam gear.  With another set of holes in the camshaft gear I will be able to adjust the cam timing. 





Then I proceed to turn the remaining  bearing surfaces on the cam shaft.





Below is the camshaft nearing completion.  It still requires some polishing of the bearing surfaces and cam lobes, as well the removal of the extra material on the far end.


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## Carbuilder (Apr 22, 2022)

This is very impressive work and I really appreciate the level of detail you show. I never think about using the 3D printer to make fixtures for machining. Also, the cylinder liner info will help when I get to that on my Little Demon engine. 

It gives me a work quality to aim for. 

Rick


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## ofaf (Apr 23, 2022)

VERY nicely done!


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## minh-thanh (Apr 23, 2022)

It will be a great engine !


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## Eccentric (Apr 26, 2022)

*Cambox and Camshaft Bearings*

The Cambox houses the overhead camshaft, its bearings and the cam followers.  Since I have completed my first camshaft, I will move on to the first Cambox.






I start with an oversized work piece, fly cut the top and square off the front end.  On the second cambox I will not bother fly cutting the top surface as it gets machined away.  I drill the four holes for the cam followers undersized so the 1/4" end mill does not need to plunge cut.  These will be milled out further so a 3/8" reamer can finish the cam follower guide holes.






I use a 1/4" end mill to rough and finish the cam follower holes, horizontal and vertical surfaces; a 3/32 flat end mill to rough out the trough for camshaft lower bearing surfaces; a 3/16 ball end mill to "finish" the lower bearing surfaces; and finally a 1/16" flat end mill to create the holes for the camshaft bearing hold down screws. I put "finish" in quotes as the bearing surfaces will be reamed later.  The bearing hold down screws will eventually pass through the cambox through clearance holes and screw into the cylinder head.  But I will drill undersize and tap the holes first so I can clamp the upper cam shaft bearing clamps in place to ream the camshaft bearing surfaces.





Above is the final milling operation with the ball end mill. And below the machining has been completed on the top surface of the Cambox.


The bottom surface will be machined once the gears have been depthened and then the side surfaces will be machined last as they are cosmetic.





Now on to machining the camshaft top bearing caps.  they will be machined as a group, then separated on the band saw, and their ends finished on the mill.





3D model of the bank of camshaft bearing clamps. The ears on the sides will be machined off later, they are vise stops and will be used instead of parallels in the vise.  They provide the required space for the milling tools to clear the vise.





Below the work piece has been finished to size.





Then the bottom is machined....





The top is machined....





And the finished group of top camshaft bearing caps are shown below:





I am pleased with the registration of the top machining to the bottom machining.  This can be seen in how well the top machined countersinks match the screw holes machined from the bottom.





The individual caps are seperated on the band saw and then finished to final length on the mill.





The bearing caps are clamped into place using a properly sized rod to align them, and then the camshaft bearing surfaces are reamed to size.  I used a 6mm reamer because my imperial reamer set is in 1/16 increments--a .250" reamer was too big and interfered with the 2-56 hold down screws and I felt the .1875" reamer was too small for the camshaft bearing surface.  So I used a .2362" reamer, known by some as a 6mm.





Then I move on to the second camshaft....





I turn on centers and machine as close to the collet as possible, extending the camshaft out section by section as shown below:





I take small cuts, advancing the cross slide .0025" at the most each cut.





Below the first camshaft is installed in the cam box and the second camshaft is in the same state as the first.





Then the second cambox, below the camshaft bearing surfaces are indicated after reaming.








Second Cambox top machining complete.


I am now going to turn my attention back to the gears.  I have decided to attempt making my gears out of 1144 stressproof steel, but so far I have not had good luck.  I ruined my cutter on the first attempt. I am sure I ran the cutter spindle speed too high.  I took 4 cuts per tooth working up to .045" depth.  If you look at the bottom of the steel gear you can see where the teeth start out OK, but as the cuts work their way around clockwise the cutter wears out.

Below is a 1144 steel gear blank on the left, a failed 1144 steel gear in the middle and a brass gear that meets print.  I have bought another gear cutter and I will try slowing the spindle speed way down on the cutter, take small bites and lots of oil.  We will see.....


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## Eccentric (May 2, 2022)

*Offy – Cambox Covers*
Cambox Covers
The cambox covers mount to the top of the camboxes and enclose the camshafts.  They are often polished aluminum and are a distinctive feature of the Offenhauser engines.





In my scale they are sections of a .67″ tube–a non standard dimension. I thought of several approaches to their fabrication and settled on using .625″ OD tubing (.065″ wall) and stretch it to size using a form tool.
First I turn the outside of the tubing on the lathe and polish it, first with scotch brite, then fine steel wool and finally polishing compound on a rag.





Below are the polished aluminum tubing work pieces.  One I turned using a carbide insert and the other a HSS rounded tool.  The HSS tool had the better finish.





Next I machine a .35″ slot in the tubing, leaving extra material.





Below are the tube sections with the slot cut.





As mentioned above a form tool is used to stretch the tubing to the proper diameter. The female part of the form is 3D printed and the male part of the form is an aluminum rod turned to size.  The form tool is shown below.





Then, using the mill vise, I press the male form tool into the split tubing.





The tubing section is more than a 1/2 section, so the male form tool pops into place.





Below is the split tubing now sprung to the male form tool.





I press the male form tool free of the tubing section and now have my .67″ diameter tube section.
Next I drill the 5 holes that will be used to mount the cambox cover to the cambox.





Below the holes are cleaned up.





Then the tube sections are screwed to the female form tool which will be used as a holding fixture.





This is clamped in the mill vise on parallels.  The fixture will orient the work piece so the holes will be in the top center of the finished cambox cover.





The bottom of the cambox cover is machined to set the total height of the cover.





Then a notch is machined into the bottom of the cambox cover so it fits tightly to the cambox.





Below is a finished cambox cover snapped in place on top of a cambox.





The 3D model showing the notch feature of the cambox cover:





And a closeup of the finished cambox cover mounted on top of the cambox.  Note that only the top machining has been competed on the cambox.





Below the cambox cover is in place and shows the clearance between itself and the camshaft bearings which double as attachment points for the cam cover screws.





And finally the finished cambox covers.


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## Eccentric (May 9, 2022)

*Offy - Gaskets Part 1*


Gail (@GailInNM) was kind enough to cut gaskets for me on my last engine.  This time around I decided to develop the capability myself.  It is something I want to be able to do going forward.

My first task was to procure PTFE film in .005", .010" and .020" thicknesses.  Fortunately, a plastic supply house is located within reasonable driving distance.  Unfortunately, they do not like to deal with the little guy.  I wanted a couple of square feet of each.  They brought out the quote- 25$ per thickness, $75 total.  They wanted to charge me a minimum of 1 pound of each size at $25 a pound.  Who ever heard of such a thing, who buys rolls of PTFE film by the pound? Well I found another outfit that sold the film by the foot at pretty reasonable prices, but the shipping was $20.  I bit the bullet and spent a total of $55 for the PTFE film I needed and have enough for several engines.

My second task was to obtain a cutter, after some research I settled on this from amazon:







I decided to use the 3D printer to do the cutting. The reason I decided to go this route was that the 3D printer has an auto bed leveling feature.  The cutter needs to be held at a very consistent distance over the material being cut. 

I used Fusion 360 to create the tool path.  I could not make Fusion 360 create a Gcode file the 3D printer was happy with, the formats were too different and I could not find a post processor to do what I wanted.  So I wrote a Python script to convert from "milling" Gcode to "3D printer" Gcode.  This of course took some trial and error to get right.






I then made a bracket for the cutter for my 3D printer. 

Well, after about a week of developing and improving the adapter to allow the cutter to be mounted to the 3D printer carriage, and getting good Gcode, I began making test cuts.  But like so many other things in our racket, the 3D printer carriage was not rigid enough; all of my circles came out as ovals.  A 3D printer print head is not designed to take much side load. Instead of continuing any further I decided to switch to the CNC router.

I made an adapter for the cutter so I could mount it in an ER25 collet in the CNC router. The Gcode from fusion 360 could be used directly on the CNC Router.







This worked much better.  Below is a picture of the results of my first attempt at making gaskets on the CNC router.






Next time I will cut all of the holes first and the outlines last.  Once the outlines are cut, the gaskets can move around a little, and the holes do not come out perfectly round.

Now I need to design the rest of the Gaskets.


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## propclock (May 11, 2022)

Fantastic Gasket. 
Some questions please. Does Fusion calculate drag
cutting offset to the cutter? Does the blade stay in contact with the material 
between locations of separate cuts? How did you hold the ptfe to the 
cutting surface . Did you make your own rotating bearing cutter holder?
If so how much offset did you use? 
  This interests me, and all details would be appreciated. 
Thanks and sorry for all the questions.


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## Eccentric (May 11, 2022)

Gaskets - Part 2

Below is a complete set of Gaskets for the Offy.






To get a hard flat surface I started with a block of wood clamped in the vise.  A wood router bit was used to level the surface of the block. 






A slab of Corian was screwed to the wooden block to provide a hard flat work surface.






I simply taped a piece of cardboard to the Corian to give me a backup cutting surface, and then taped the PTFE (teflon) sheet to it.




As mentioned in the last post I purchased a vinyl cutter from Amazon.  It is a pretty neat little deal, the height of the cutter can be adjusted and locked into place.  A magnet pulls the cutter in and holds it.  I turned a simple adapter ring so I could mount the whole thing in an ER25 Collet






Below is the cutter assembled:






And mounted in the 1/2" collet:






The spindle is off during the cutting operation and the little cutter can rotate in its housing to act as a "drag knife".  No special code is required, simply trace the outline of the gasket with the cutter.

Creating the Gode was done in Fusion 360 using a DXF file of the desired outline, then a trace operation was used.








I organized the file so the small holes where cut first, then the large holes and finally the outline. I placed small .010" gaps in the outline of the gasket so it remains intact during the cut.  Above you can see the green lines where the cutter is lifted and the yellow lines that represent rapid moves to the next cutting location.  The cut lines are blue.

@propclock , To answer your specific questions:
Does Fusion calculate drag cutting offset to the cutter? - this is not required as the little cutter is so small and acts like a drag knife.

Does the blade stay in contact with the material between locations of separate cuts? - The cutter is only in contact with the material when it is cutting, it is lifted to move to the next cut.  See cut profile above

How did you hold the ptfe to the cutting surface . - Painter's tape

Did you make your own rotating bearing cutter holder? - No, just the adapter to the ER25 collet.

If so how much offset did you use? - Again, no offset is required.

I hope this helps.


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## mayhugh1 (May 11, 2022)

Nice work on the gaskets. I do something similar on my Tormach. For a work table I used a piece of two inch thick formica covered table top. A heavy metal bracket bolted to its bottom allows me to mount the table in my vise and most the top is surprisingly normal to the spindle axis. For a compliant cutting surface I purchased a cutting mat from a sewing notions store and taped it down to the top surface. The whole thing works great, but over time a few crashes have limited the areas I can still work on. - Terry


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## propclock (May 11, 2022)

Thank you very much for the details . I ordered the cutters,& holder yesterday and they arrived today.!
I spent a lot of time looking at cambam drag cutting but I guess I don't need any Yea!
Time to play. Again thanks for the details.


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## Eccentric (May 23, 2022)

*Offy – Camshaft Gear Caps*
The Caps that cover the Camshaft Gears are small parts, but pretty complicated to fabricate because of all the small features on all sides.  It is challenging to maintain registration of the features on the four sides needing machining.

The caps are shown on an engine below:





The 3D model:





The dimensioned print:





Fusion 360 was used to create the tool paths for the CNC router.  There is a roughing pass with a 1/4″ flat end mill, and a finishing pass with a 1/8″ ball end mill.  The four holes are spot drilled with a 1/16″ mill, with a follow up on the manual mill to drill them to size.





Below is the roughing pass:





Then the finishing pass from the top.





The finished machining of the top of the cap.





The manual mill is used to drill a 1/4″ pilot hole before machining the sides.





The top and sides of the cap stand offs were used to touch off the CNC router before machining the front side.





Below is the result of the front side machining.  .010″ material was left on the bottom to be machined off when the bottom is machined.





then the back side machining is done:





And finally the bottom machining is performed, first with a 5/32″ flat end mill, then a 1/8″ ball end mill.  Sinde the bottom of the part was machined off and the Z-axos zero was lost, the two end mills used the top of the vise to zero the Z-axis.





finish machining of the cap bottom:





The caps ready for bead blasting:





And a cursory test fit on the engine:





Below is a fun picture of the gears installed in the gear tower.  I have made two attempts to cut steel gears, but they both failed.  I am not giving up on cutting a full set of steel gears, gotta try again.


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## propclock (May 24, 2022)

wowser! fantastic work


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## mayhugh1 (May 24, 2022)

Eccentric,
Again, really nice job. If it's any help, I cut my Stressproof gears at 250 rpm, 3 ipm, and .010" depth of cut. I believe my cutter came from Travers. - Terry


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## Eccentric (May 24, 2022)

Terry,

Thanks, that is a lot of help.  My spindle speed is too fast and my first attempt was WAY too fast.  I will give your speeds and feeds a try. The cutter has a lot of cutting edges per revolution so 250 RPM for a gear cutter is not the same as say a 3 flute end mill.  I have been using the CNC router to cut the gears, but the spindle will only go down to 600 RPM (10Hz * 60 seconds/minute). I will set up on the manual mill where I can slow the spindle down, but will have to feed manually.


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## mayhugh1 (May 24, 2022)

My numbers are probably way conservative, but for CNC I can walk away and mow the lawn while the gear is being cut. If you do it manually you might want to be more aggressive on the depth of cut so you don't fall asleep at the wheel. It sounds like you were just running too much rpm for a 1-3/4" diameter HSS cutter in steel. Stressproof really does machine nicely. For a large number of identical gears I also cut a single thick blank and part off the individual gears later since I only have one yard to mow. - Terry


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## Eccentric (Jun 21, 2022)

*Offy – Ring Stress Relief Fixture*

I use George Trimble’s formulas for the dimensions of my rings and the stress relief fixture.  I have a print for this fixture that is parametric, that is I update the dimension of my cylinder bore and the rings and the CAD program does the rest of the calculations for me.











The only tricky part about machining the fixture is the requirement to drill the hole for the ring gap pin before the machining of the finished diameters on the lathe.  I start in the lathe with round steel stock, face it and drill the center 3/8″ hole for the clamping bolt.  Then I pull the work piece out of the lathe and set it up in the mill.





I use a wiggler to find the center of the large hole, then use the DRO to offset to the position of the ring gap pin.





When I return the drilled work piece to the lathe I use a centering bearing in the tool holder and a live center to insure I am reasonably back on center.





I turn the two parts of the ring to dimension.  Below I am using the end cap to properly size the OD of the ring holding fixture.  This OD is the critical dimension for the fixture along with the position and diameter of the gap setting pin.





Below is picture of the finished fixture.  Care must be taken to remove any radius at the bottom of the fixture so the first ring seats flat.  I usually use a sacrificial ring at the bottom with a filed internal chamfer to insure the rings sit flat.


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## Eccentric (Jun 27, 2022)

*Offy – Rings and Pistons*


I like to make my cylinder sleeves first, then my rings to match, then finally my pistons.  I do this so each matches its predecessor if there are any discrepancies.  This time around I did a good job of making the cylinder sleeves match, only one was different and it was only by .001″.   I made 13 rings, needing only 8, with all spot on the ID and OD.  But I did not do a great job repeating the height of the rings, this is due to my skill at repeatable setting the zero point on the lathe carriage or the positioning of the cut off tool.  I use the razor blade zeroing method, but any way I had a variation of .0299″  to .0342″.  I made my pistons match the cylinders and the piston grooves match the ring’s height.

To cleave the rings, I put a piece of tape as shown below and score the top and bottom with the fine edge of a diamond file.  The tape helps align the scoring on the top and bottom, I rest the file against the edge of the tape and drag the file.





I use a razor blade and a slight tap with a hammer to cleave the rings at the score mark.





I then measure and sort the rings, light test them, and assigning them to cylinders.  I turn the pistons matching the ring grooves to the rings.
When I heat treat the rings I first heat them to about 400 degrees F, pull them out and coat them with a slurry of Boric Acid and Isopropyl Alcohol.  The alcohol boils off and leaves a nice crust of the Boric Acid.  the picture below shows the rings in the stress relief fixture after heat treat.  The rings are protected from oxidation.





Below is another picture after the fixture and rings have been soaked for a minute in boiling water.  the Boric Acid dissolves revealing the finish on the rings.





Then to making the pistons






Below the sorted rings and pistons still attached to the work piece.  the rings are stored in bags with labels and some oil to prevent rust.





Below I am using the mill to drill the gudgeon pin hole.





And below I am removing some material from the top of the pistons to clear the valves in an excess of caution.










then I remove the pistons from the work piece and drill 1/4″ holes down in the bottom of the pistons to ease the machining that will be performed on the CNC.





Below is a cutaway of the piston showing the internal cut out required to leave enough material for the rings.  Also is shown the worst case valve piston clearance.







Then the tool paths are created and simulated:





Next I will finish the inside of the pistons on the CNC router.
——————————————————————————————————–
Below is a summary of the steps I use to make piston rings:

I put the cast iron slug in a 4 jaw chuck for the max gripping power and rigidity.
I turn the ring blank down, leaving 300% material, so instead of .050″ thick, I turn down to .150. So, for a 1″ internal cylinder bore, the ID of the blank would be about .9″ and the OD would be about 1.05″
Pull the blank out of the lathe and Stress Relieve in the heat treat oven – 1000 to 1050 degrees F for an hour and a half.
Furnace cool to less than 200 degrees F before air cooling the rest of the way down. Usually I just leave it in the oven over night.
Put back in the 4 jaw chuck centering as well as possible. Turn the ID on the ring blank to final dimension, then turn the OD to final dimension. Finish the OD with emery paper.
Part the rings off.
Wet sand (with light oil) on a piece of glass with 400 then 800 grit paper to clean up edges and get to proper height.
Cleave the ring gap. I lightly score the top and bottom of the ring with a fine file, then use a razor blade to cleave the ring. I hold the razor blade so its cutting edge is in the filed groove, then tap the back of the razor blade to cleave the ring.
Use a fine diamond file to clean up the gap and get it to .004″ in the cylinder sleeve using feeler gauges.
Use an Arkansas sharpener’s ceramic rod to clean up inside edges.
Clean the rings and the heat treat fixture with acetone.
Clamp rings into the heat treat fixture. Clamp means finger tight, everything will expand with the heat.
Set the heat treat oven to 1050 degrees F and place the loaded ring fixture into the oven.
When the oven reaches a temp of about 300 to 400 degrees, pull the fixture out of the oven and rub a slurry of boric acid and isopropyl all over the exterior of the rings. This does a good job of preventing scale, it is easy to see where you miss a spot after treating.
Stress Relieve the rings in the heat treat oven – 1000 to 1050 degrees F for an hour and a half. (my reference is the study performed by the Naval Research Laboratory on stress relieving cast iron dated 1948)
Furnace cool (over night) to less than 200 degrees F before opening the furnace.
Remove the fixture and drop into a tin can of boiling water to remove the boric acid.
Lightly scotch brite the rings exterior, then remove them from the fixture. Clean the rings as necessary.
Perform Terry’ light test to determine the quality of the seal of the rings against their cylinder sleeve.
Measure each ring, note in the log, coat each with light oil, and place into labeled zip lock bags.


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## Eccentric (Jun 30, 2022)

*Offy – Conrods Part 1*

I am going to try something different with the connecting rods. I want  to install a bronze split bushing in the big end.  It will be secured with Loctite and brass taper pins. As a warning, my first attempt was a failure as can see below:




The bushing is too thin and the material is very brittle and hard to machine.  I want the cap screw holes to clear the bushing, but the distances are really tight and the resulting bushing is too thin.

To back up a bit, the following images are of the desired connecting rod.  It is not symmetrical as can seen in the side view due to the geometry of the crankshaft with respect to the pistons–the big end is offset from the piston center.







Below is the material squared up and ready to go, fortunately I only make one to start with.




I drill a clearance hole in the work piece to facilitate CNC machining.




Then I turn the bronze bushing to size.




The big end profile is machined:




The hole is reamed and the bronze bushing is installed with Loctite.







The end cap has the cap screws holes drilled/tapped and countersunk.




A slitting saw is used to separate the cap.  I use a 1/32″ thick saw blade.




so far, so good. 




The surfaces are wet sanded and then the cap is screwed into place.




I then drill and ream out the big end hole.  This is where things went awry.  Perhaps the drill was not sharp enough, I got too aggressive, or the design was simply poor not allowing enough bearing material.







The gudgeon pin hole was drilled and reamed.




And again the end result:




So I redesigned the Conrod.  I moved the cap screws outward to allow for a thicker bearing and I added some material to the con rod cap.




Below is the beginnings of a second try.  Here I have completed all of the above steps to the point where I am letting the Locktite cure–that will be over night.  The bronze bushing diameter the first time around was .4385″, the second attempt is .499″.  The ID will be .375″, so I will have more meat in the bushing, but less in the cap.




So, I am now waiting for the Loctite to cure. I will report back after the rest of the conrod machining is complete.


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## Vietti (Jun 30, 2022)

I wonder if you used a softer, less brittle bronze alloy.  Looks like bearing bronze, tough stuff!


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## Eccentric (Jul 1, 2022)

Using a softer bronze is a good suggestion, I do have some softer Bronze that I have designated for use in making the valve guides.  I had some bronze bushings laying around and thought I would give them a try.  It requires some special attention when machining.  Below are a couple of snaps of my second attempt.










I am please with the design changes to the connecting rod.  The bronze bush is thicker and the cap looks substantial enough.  I also was very careful when machining the bronze.  I used lots of oil and stepped up one drill size at a time.  

This conrod blank is ready for the outside "cosmetic" machining.


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## propclock (Jul 1, 2022)

Is it just me? I am not getting a lot of your pictures?


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## Basil (Jul 1, 2022)

Eccentric said:


> Using a softer bronze is a good suggestion, I do have some softer Bronze that I have designated for use in making the valve guides.  I had some bronze bushings laying around and thought I would give them a try.  It requires some special attention when machining.  Below are a couple of snaps of my second attempt.
> 
> View attachment 137577
> 
> ...


A lot simpler than the solder method I have seen. The bushing is locked in place very nicely due to its ovality and of course the locktite


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## Weldsol (Jul 2, 2022)

Eccentric said:


> *Offy – Conrods Part 1*
> 
> I am going to try something different with the connecting rods. I want  to install a bronze split bushing in the big end.  It will be secured with Loctite and brass taper pins. As a warning, my first attempt was a failure as can see below:
> 
> ...


That material looks a lot like oil lite bush material ? which is a sintered material and difficult to get to very thin wall due to the particle size so bits fall off

Paul


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## Eccentric (Jul 5, 2022)

*Offy – Conrods Part 3*
I have spent the past weekend developing the tools paths to machine the outsides of the Connecting Rods.  I will be using the fixture shown below to hold the conrods so the entire side can be machined in one go, then it is flipped over and the opposite side is machined in a like manner.
The fixture consists of two drill rod posts fitting in the big and little ends of the conrod and hold down screws clamping everything tight.




The first roughing operation is to machine the outline  and remove most of the material.




Then the top side is machined:




The part is flipped over:




And the back side is machined:




And below the conrod pulled off the CNC router.  Now to machine the other three connecting rods.




I am pleased how this technique of installing a bronze bushing worked out. Next time I won’t use an off the shelf oil-lite bushings, but some softer bronze stock.


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## Eccentric (Jul 8, 2022)

Offy – Vavle Guide​Today I started fabricating the Offy’s Valve guides.  Below is the result of the first one:





I don’t have  any aluminum bronze (954) on hand, but I have a stick of phosphor bronze so I will use that for my valve guides. I started with the 1/2″ diameter bronze stock chucked up in lathe, faced it and spot drilled it for the large hole.  Then before drilling the large hole I spot drilled for the smaller through hole, and drilled the small hole all the way through.  The technique of using a large spot drill followed by a small spot drill is an interesting technique and is supposed to insure two holes of differing sizes are drilled concentric.





Then I drilled the larger hole to the proper depth, and turned the outside diameter to .374″. I coated the part in Dykem and cut the valve seat at 45 degrees.  It is a really small seat, about .010″





then I used a cut off tool to complete the outside machining.





I have a DRO on my lathe and have come to really enjoy it.  For a long time I did without, and even when I first got it on a whim I didn’t utilize it fully.  It took me a while to trust it.  But like I can’t imagine not having a DRO on my mill, I now can’t imagine not having the DRO on the lathe.  When making multiples of a part, for example I need eight valve guides, the DRO makes the machining process so much smoother.  I still use the micrometer for all final dimensions, but I can hit them with the DRO repeatably.










Below are a couple of images of the valve guide test fit in the head.  I still need to machine the hole in the side of the valve guide, but I will do all of the valve guides at once in a single set up on the mill.








My original design called for a .093″ valve stem, but when I was drilling and reaming the small hole in the valve guide I began to second guess my ability to make a valve with such a small stem.  I revisited the design and decided I have room for a valve with a 1/8″  stem.  So I redesigned the valve guide and valve for the larger 1/8″ valve stem.  the valve now looks like this:




I have a fatter stem through the valve guide, but neck it down to maximize the flow into and out of the cylinder.


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## Vietti (Jul 8, 2022)

Fantastic work!  I wonder how you are going to secure the valve guides in the head?  I have used Locktite stud setting formula and still had some leaks..   The problem was solved with the wicking threadlocker Locktite   This is a very useful product and its ability to creep into places is fantastic, sometimes too much so!


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## propclock (Jul 8, 2022)

Just my 1.414 cents worth I use Loctite 680 for cages with no issues .


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## petertha (Jul 8, 2022)

My bronze valve cage is similar to yours. I have to check my notes but I think I used 620, the high temp version, for bit of insurance. Judging by some torch testing I think (I hope) it will stay put.

One thing to mention is Loctite sets off crazy fast on bronze for some reason. Good thing I experimented on a tester because it may have caught me off guard.

My thought was that that an easy slip fit might help minimize potential distortion vs a close or interference fit so long as its within the prescribed annular gap. Time will tell if this was the right approach. I did the final seat cutting in-situ once glued in.


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## mayhugh1 (Jul 9, 2022)

Vietti said:


> Fantastic work!  I wonder how you are going to secure the valve guides in the head?  I have used Locktite stud setting formula and still had some leaks..   The problem was solved with the wicking threadlocker Locktite   This is a very useful product and its ability to creep into places is fantastic, sometimes too much so!


Ron Colonna used Loctite (don't know which variety) but told me he had issues with his exhaust valves coming loose. When I did mine, I used Loctite 620 and for safety pinned them in place with steel pins. Steel wasn't necessary and will make them more dufficult to remove should the need ever arise. Care is needed to secure them at their edges without actually penetrating their interiors. - Terry


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## Eccentric (Jul 9, 2022)

Yes, I will be using Loctite to retain the valve guides in the head.  I had planned to use 638, but looking at the Loctite chart Peter attached 620 is intended for higher temperatures.  They recommend an "Activator", which I have never used.  It is a good tip to be careful of it setting too quickly, once Loctite sets it is difficult to remove without lots of heat.

I will also be following Terry's lead and installing small pins to secure the valve guides.  The two pictures below show the predrilled holes for these 1/16" pins.  The first shows the entry point of the pin, and the second shows the hole just breaking through where the valve guide will be installed.  It intersects the valve guide high up where there is plenty of material to bite into.













The reason I have chosen to cut the seat in the valve cage before installation in the head is two fold. One, I have a lot of time invested in the head and would hate to mess up a valve seat and lose the head.  Secondly, I make my valve cages and valves as matched pairs, testing them individually under vacuum before installing the valve cage in the head.    I drill the valve guide holes and cut the valve seat in the same set up in the lathe and think I can maintain good concentricity this way.

Good discussion, thanks guys.


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## Eccentric (Jul 13, 2022)

Offy – Vavles​This is a quick update on my progress, I am working on fabricating the eight valves for the engine.





I cut the 45 degree seat and large radius with the lathe in reverse to facilitate access of the tool.





And below is the valve ready to be lapped into the valve cage.  I leave the slug of material on the face of the valve for this purpose, this of course will be removed later.


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## Eccentric (Sep 13, 2022)

Offy – Exhaust System​
Below are a couple of photos of Offenhauser Exhaust systems.  Mine will be fabricated from a brass flange plate, four 3/8″ 90 degree bent 304 stainless steel tubes and one conical collector made from a 16mm X .5mm 304 stialness steel tube.








Below are a couple of views of the 3D model.  Frankly I just adjusted the lengths and conical collector flare until I thought the exhaust system looked good. I reviewed Terry Mayhugh’s method for making his Offy exhaust system and will attempt to follow his lead.







Below is the most complicated part, the conical collector.  It is just under 5 inches long, 3/8″ at one end and 16mm (~5/8″) at the large end.




First I made a couple of fixtures.  The internal mandrel started as a 5/8″ diameter length of aluminum stock, tapered to match the inside of the cone.  There are two ways to machine this, the cleanest is to adjust the tail stock so it is offset to one side, the difference between the two radius of each end of the cone. Then turn on centers.  I chose a second method because I did not want to have to re tram the tail stock when I was done.  So I used the compound to cut a taper equal to the cone angle.  I took cuts in 1/2″ increments down the length of the stock, resetting the compound as I went.





I 3D printed female molds of the cone as shown below using 9 layers around the perimeters and 60% infill.  These forms are almost solid plastic.





I cut a triangular notch out of a length of 16mm tube using a Dremel cut off wheel, then used the mandrel and forms to shape the cone closing up this gap.  This was very tricky and the .5mm thick stainless steel was not easy to reshape.  I then welded the slot closed, this was also a very tricky operation as the .5mm (~.020″) thick SS is very hard to weld without just melting it.  I made a bit of a mess, but the part came out OK after grinding.  I don’t know if I could do any better on a second try.  I suppose I could go back and fill in some of the voids with the MIG welder, but it is so easy to just punch a hole in the tube.  I will try to fill the last voids with silver solder later.  I have not decided what finish I will use on the exhaust system, nickel plate or just a black high temp coating.





I then bent the four 3/8″ diameter SS tubes.





I machined the exhaust flange plate that will mate to the cylinder head out of brass sheet.





This is where I stand now.  I have a little more thinking to do.  I want to cut the three holes in the side of the collector tube to match the bent feeder tubes, but am having problems with my CAD program.  I thought I could punch the holes as shown in one of the earlier CAD images of the collector tube, then unroll it, or flatten it, like a piece of sheet metal, but I am not having any luck.  Then I could print this out on a piece of paper, over lay it on the collector tube, mark and cut the holes.  This still seems the best plan, I just need to figure out how to make SolidWorks cooperate.





I will make a rigid fixture to hold all the parts in the correct orientation so I can easily silver solder it all together.  I need to think about this a bit as well.

All for now, I think I have completed the difficult parts.


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## propclock (Sep 13, 2022)

Excellent !, very enjoyable following your work. Thank you.


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## Eccentric (Sep 27, 2022)

Offy – Exhaust System Part 2​I modeled the exhaust collector cone in CAD and then flattened it to give me a pattern of the holes as shown below:





I glued this on and then machined and ground out the material.

Below is a test fit of one of the bent tubes:





Next I grabbed a piece of scrap aluminum and made a fixture to hold the exhaust system in the proper position for silver soldering.





Below is the exhaust system ready to silver solder.  Or so I thought.





In hindsight there is a bunch of stuff wrong with my fixture.  And I found out the hard way.

The 1/4″ plate that I used to secure the exhaust flange acts as a heat sink and wicks all of the heat away from flange as it is silver soldered.  An excessive amount of heat was required to get the silver solder to melt, and it ended up just globbing up at the joint.  I had to come back later, reheat and shake off the excess.
I used thin strips of aluminum held together with very thin stainless steel wire to align the feeder tubes.  The thin aluminum strips ended up melting and dribbling all over the collector tube and the thin stainless steel wire simply vaporized.  Primarily due to excessive heat, see 1. above.
Below is the exhaust system as it sits now.  It is functional and I may use it for initial engine checkout, but I have all the material for a couple more tries.





This is only the second time I have attempted silver soldering and I know that I need a better fixture and more practice. 







Doc, one of the remaining flying Boeing B-29s visited my air field this last week.  This amazing World War II era bomber holds a special place in my heart as my father regaled me with many SuperFort stories when I was a kid. He was in the Air Force, and as a B-29 engine mechanic his time in the war was spent at forward Pacific island air bases keeping them flying.


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## Basil (Sep 28, 2022)

_A little bit of carefull handwork and I think that will still clean up nicely. Are you going to finish it with a high temp paint?_
_Just a thought, could you have chamfered the holes in the engine side of the flange and silver soldered from that side. I can appreciate the difficulty with such thin stainless. I tend to have good luck sometimes cutting and placing the solder, lots of different angles so I can appreciate the issues with trying that. I have some very small diameter regular solder that I coil around a joint maybe they offer a small diameter silver solder wire.
Hate it when the base metal is bright hot and the little bit of solder is sat there doing nothing 
Of course lots of bright ideas after the fact, that’s easy! 
Nice job though and again I bet it cleans up nicely._


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## Eccentric (Sep 29, 2022)

Offy – Intake Manifold​
I like the look of the original dual side draft carburetors as shown in the following photo:






However, I have never made a carb before and want to start with a single carb set up for initial engine checkout.   

That is what I am going to fabricate here and this is the design I have settled upon:







Below is the flange that mounts to the cylinder head being made on the CNC router.  In the lower left hand corner is an ice chip that I used to keep the part cool during machining.  My mister broke and I didn’t want to wait until another was delivered.  When machining parts that use 5-minute epoxy as the hold down strategy, the parts needs to be kept cool, or the epoxy will soften or even give way and you end up with a ruined part at the least.





The end caps were machined from the solid.  I took a 30 degree cut removing most of the material, then rounded the part with a file on the lathe.





A step was then machined before parting off so the cap fits snuggly in the larger intake tube.





The large cross tube is .5″ in diameter, so I used a .5″ end mill to shape the intake runners and the carburetor  mounting tube.





Below the parts are test fit.  I decided to solder the assembly together first, then machine out the holes in the large cross tube.  I think this will simplify the alignment of the parts during soldering.




I am still formulating my soldering strategy.  My thought is to  solder the feeder tubes to the flange first, then the cross tube to the feeder tube and the carburetor tube last.  Jewelers often use different formulations of silver solder that have slightly different melting temperatures that allow them to stage assembly of a piece.  They use the higher temp solder first, the idea being they do not need to raise the temp of the piece as high for subsequent solder operations and not disturb previous work.  The single roll of silver solder I have nearly broke the bank, so I am not going to be purchasing additional types.


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## CFLBob (Sep 29, 2022)

Don't forget that jewelers don't typically buy a pound of solder; they buy ounces or fractions of ounces.  Especially small shops and hobbyists.

These guys are one of the big name suppliers in the US. 









						Silver Sheet Solder Assortment - RioGrande
					





					www.riogrande.com
				




1/4oz each of four different grades of solder.  I'm sure you could look around and find other options.


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## peterl95124 (Oct 5, 2022)

Eccentric said:


> I am still formulating my soldering strategy.  My thought is to  solder the feeder tubes to the flange first, then the cross tube to the feeder tube and the carburetor tube last.  Jewelers often use different formulations of silver solder that have slightly different melting temperatures that allow them to stage assembly of a piece.  They use the higher temp solder first, the idea being they do not need to raise the temp of the piece as high for subsequent solder operations and not disturb previous work.  The single roll of silver solder I have nearly broke the bank, so I am not going to be purchasing additional types.



I really like the look of your exhaust manifold, it should clean up nicely, and for the intake my advise is to braze the stubs to the main tube first (using the flange plate to hold them in alignment) then turn it over and gravity will hold them together when you're brazing to the flange plate.  I've tried the method of different melting point solders but have found it unnecessary, a previously brazed joint is very hard to melt all the way around so even if it partially re-melts the piece won't move, and they seem to be highly resistant to re-melting anyway.   I use 56% for close fitting parts and 45% for gap filling, and don't hesitate to do multi step brazing regardless of the silver formulation MP.

back to fixturing, I brazed the flanges only my exhaust tubes by screwing the flanges down to a steel bar with mica insulation in between. the mica didn't really insulate thermally as I had hoped, the steel bar got almost red hot, but it did prevent the flanges from accidentally getting brazed to the steel bar.  I think "machinable alumina" would work as an insulator, but these days its another "break the bank" item, so sadly I haven't bought any since Small Parts Inc went out of business.

I think an Offenhauser derivative (maybe "standoff scale") will be in my future.  So many thanks for sharing.


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