Coated bearings question

[Aurel]

If you had a crankshaft that was slightly below the wear limit on the mains, rather than regrinding it one size under, would it make sense to just polish it, buy a set of standard bearings and send them to calico for coating a dry lubricating film inside the bearings with enough thickness to bring the tolerances back into specs? I am pretty sure they can coat any thickness we ask, not sure what the maximum is. Just a thought...then if you had spun a rod bearing, do the same on a new rod bearing...I wonder if this has been tried before.

[HawgRyder]

Unless the applied film was hard enough to be a permanent bearing surface...I think it would just wear away quickly...and leave you with a loose bearing.
Back in the days of flatheads..etc...we used to pack the back of a bearing with shim stock to reduce the clearances.
I'm not suggesting you do it...but just be aware of how the old guys saved money...LOL
Bob

[Henry Schmidt]

Originally Posted by Aurel

If you had a crankshaft that was slightly below the wear limit on the mains, rather than regrinding it one size under, would it make sense to just polish it, buy a set of standard bearings and send them to calico for coating a dry lubricating film inside the bearings with enough thickness to bring the tolerances back into specs? I am pretty sure they can coat any thickness we ask, not sure what the maximum is. Just a thought...then if you had spun a rod bearing, do the same on a new rod bearing...I wonder if this has been tried before.

Coatings may work for awhile but it would be a hit or miss remedy.
How much under are we talking about?
If the number is minor you'll probably fine. Eight main bearings on a six cylinder engine gives you a pretty stable platform for main bearing stability. Remember to use cam flow reducers and updated pressure relief springs and caps to maintain oil higher oil pressures. There is a train of thought that says high larger clearances with high oil pressures is how you generate horse power. BMW and Chevy race engines seem to employ this theory.
If you have a 9 bolt crank, you could buy a set of GT3 main bearings in the smallest size (I think red). They come in tree different sizes for custom fitting of race cranks.

[nocarrier]

You might be able to have the crankshaft nitride hardened to bring it closer to spec.

I believe the crank will actually "grow" (for lack of a better term) a little after the hardening process.

[Aurel]

Thanks, I appreciate the input. The mains are about 10 microns under minimum. It looks like I could have been fine with that, but the big issue is the spun rod bearing, which took about 170 microns of the crank on the #6...

[AlfonsoR]

You might be able to buy a good used crank for about $800....maybe less than the total cost of coatings and other special tactics.

[Walt Fricke]

My notion is that race motor cranks with rod bearing damage are candidates for conversion to Chevy (or is it something else?) rod journal sizes, so Clevite rod bearings can be used. Of course, you need different rods also.

[Aurel]

Originally Posted by Walt Fricke

My notion is that race motor cranks with rod bearing damage are candidates for conversion to Chevy (or is it something else?) rod journal sizes, so Clevite rod bearings can be used. Of course, you need different rods also.

I found a good used replacement for mine, so my damaged crank will be for sale very soon.