# Radial engine crankcase



## PeterT (Oct 28, 2016)

Some of you have seen my cylinder parts work in progress. Now I'm proceeding on the center guts, specifically the crankcase. I have not done this sort of work before & figured there would probably be some learning's.... and there were   Actually operations went quite smooth, so I figured I was going to be 'that guy' who broke his tap off in he proverbial 'last hole'. Turns out I had a more fundamental problem.

I dialed the donut block in longitudinally + square + #1 cylinder clock orientation, but completely mind blanked to check the concentricity with RT axis.  My chuck is a 3-jaw with centering plate & jaws presumably pretty accurate. Never assume! I'm not sure if the setup shifted and/or the typical 3-jaw clamping runout. But anyway some deck facets are off by max ~ 4-5 thou depending on the cylinder. Actually I could tell something was up when the internal master rod groove started breaking through unequally, which I wishfully hoped was just out-of-round grooving induced back at the lathe stage.

4-5 thou may not sound like much but it is. Unfortunately this translates into each cylinder sitting at a different deck height resulting in different compression ratio's on each cylinder. I don't want to mess with custom cylinders or modified pistons, that just gets nutty. So.... #1 is a Binner! No biggy actually, now I feel quite confident about #2 and having a spare tester is for other operations is nice.

Tooling Opinion:
I've never been super keen on my 6" 3-jaw on 6" RT combo. Its big & heavy & extended stick-out for my needs. More importantly it really doesn't lend itself to dialing in. Even good 3-jaw chucks can have 2-3 thou runout & this may vary depending on part diameter as a function of the scroll. This particular plate assembly relies on a centering do-dad & nestled registration bosses. Seemed like a smart choice convenience wise, but sources of collective error creep. So, I've ordered a smaller 4-jaw chuck (offshore Asian, fingers crossed) and will have to make an adapter plate. But if it goes according to plan I'll have a an assembly that is much easier to mount, adjust & zero part concentricity. Plus 4-jaws can hold irregular stock..


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## John Conroy (Oct 29, 2016)

Cool project. You should be able to dial it in dead nuts perfect with a 4 jaw provided your rotary table has no built in run out.


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## Janger (Oct 29, 2016)

Man you are patient Peter. Way to go.


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## Alexander (Oct 29, 2016)

Looks good Peter. For your type of project dont forget to check total runout with 2 dials at once. It is probably worth the extra effort. Very pleasing build to follow keep up the good work.


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## PeterT (Oct 29, 2016)

Alex, do you mean one dial on the OD & the other dial on the face measuring simultaneously? I've heard of 2 dials on the OD before like for lathe setup but just assumed it was checking against the part being non-round. Kind of like trying to distinguish center on a cam profile. Pretty hard unless you mapped out the readings as you rotated through 360.


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## Alexander (Oct 31, 2016)

I would just put one dial on the chuck side and the other one at the other end of it (the footstock end) this checks that the part is dialed properly. otherwise you may have a part that is not in straight and is wobbing but is off center enough that the dial reads zero all the way around.


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