vauxhall

I had many years working on kart engines. I used to put the crankcase halves in a very hot oven for 10 mins to expand the alum., the cold bearing then just falls into the bearing pockets. When the crank cases cool and shrink back to their normal size the races are locked in. Might work for you.

AndyW

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Vauxhall,

That's an excellent suggestion. Still, an issue is whether both bearing pockets in the case are perfectly aligned, one to the other, within a very tight tolerance. How much required depends on the clearances in the bearings and for very small bearings, these clearances are extremely small. This is why, even for bushings on both ends, I do the JB Weld method. My first try had bushings pressed in but the crank wouldn't spin freely. I have a Taig lathe and very simple equipment so it's not possible for me to bore both holes to very exact tolerances.

Kwink, how did you do it,,, that is, bore the two holes for your bearings?

As JB Weld can get into your bearings easily and make a mess, maybe a slip fit along with red Loctite would be safer. Any Loctite not sealed within limits (anerobic) won't cure and will simply be flushed out with the first run. That's what works for me on the inner races. All of this is became less of an issue when I went to sealed bearings though.

t_kwink

I'm pretty confident I got both pockets concentric.

First, I put the case snout in a 13/32" 5c collet. I checked the runout of the original crankshaft "journal" like this, and run-out was not even measurable with a .0001" gauge. While it was chucked up like this, I did a minimum clean-up cut of the case back (where the backplate bolts to) just to be sure it was true. I then cut the bearing pocket with a carbide 5/16" endmill that had been re-sharpened (it was the perfect size). I measured the bearing thickness at .097". Since the case was well used, I cut the pocket .095" from my touch-off to allow for the wear that was apparent on the thrust surface. I then used a 1/4" endmill and cut a little deeper (maybe .005") to give the inner race clearence. I then machined an expandable 5c collet to 5/16", and used it to hold the case the other way. I machined the collet to a perfect depth so it would hold the bearing pocket I just machined, but the back of the crankcase butted up against the collet as well to help keep things straight. I then used a live-center to help hold the snout end while I tightened the collet. I then repeated the machining operation on this side (after removing the live center). If you can follow that description, you are a better reader than I am describer...

This is the best way I could think of. All I know is that both pockets have less than .0001" runout to the original hole.


To turn down the crankshaft, I chucked in a 7/32" 5c collet, and did a minimum clean-up of the counterweight/pin area. It should come out to .500" +- .001". I also shortened the rod pin to a length of .120" at this time, like I always do. I then removed the crank and the collet. I then inserted the crank in the same collet from the backside, and rechucked it in the lathe. (now the prop end is sticking out). I then tightened a shortened prop screw into the end, and used a carbide center drill to drill a hole for use of a live center. After this is complete, I chucked the counterweight end of the crank into a 1/2" collet, and used the live center to hold the other end (centered on the drilled prop screw). I checked the run-out of this setup, and again, less than .0001". I then just turned 'er down to size, and polished a little with scotch-brite.

Sorry I'm not better at typing step by step instructions.

Wink

AndyW

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Wink,

Excellent description and I don't even have any of the equipment you describe. Many thanks. Sounds like you have everything at par. Now, if you get a lot of calls from guys flying Texaco,,,,

jetpack

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...a thought on red locktite.

What might be less risky to use than red locktite leaking into the bearings is clear fingernail polish, the cheapest you can find...it is laquer based, and if it does seep into the races, it crumbles and powders out of them without any real damage.

t_kwink

Jetpack, that's actually a great idea, not only for this application, but for many others. It's one of those old tricks that really works well, especially in a pinch.

Wink

jetpack

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Very true. I been using that trick for awhile and like it. In motor building its great, because it does hold things ok, and when its time to dis-assemble the motor it dissolves itself out of the threads easy and completely. (my small jar of brake cleaner seems to strip anything...i dont really know what removes loctite from metal besides scraping)