[Goldenblack440]

Eddie, this might be one for you...my mechanic doesn't like going over 10/10 on a crank for a mild performance motor, 20 is borderline and he throws them out if they have to go over this. I told him about your opinion that taking 30/30 off will not weaken the crank. He said that is correct, but the reason he does not do it is because he says the bearing thickness has to be much greater and because they do not make performance bearings over 10/10 (eg Clevite,) he said the cheaper thicker bearings just get chewed out very quick, creating slop.

IS this correct? I know he has some funny ideas about things sometimes, but because i don't know much about it i just smile and nod.

thanks

[dave-r]

Clevite go to 20 thou.
Federal Mogul go to 30 thou. Both are good makes.

[Eddie]

I think he means the lack of conformability,(the ability to change shape slightly under extreme load), the cheaper bearings lack. Which is why the Clevite 77's, Federal Mogul, King Alecular or the English Vandervalls are known for their high speed conformability and with steel backing material retains it's shape at high RPM's with a large amount of embeddability when things go awry. Some machinists will even machine the rods .001 more on the parting line with a shim and a rod grinder so at high RPM's under load the rods become perfectly round and able to maintain the film strength and 'cushion' at this level instead of spinning the rod bearings. But as Dave mentioned, getting them in different diameters over .010 shouldnt be a problem. Some Machinists I have dealt with are 'funny' or 'weird' they get in a certain routine and dont like change, or are plain lazy or too cheap to change tooling ectt Have you measured his finished journals with a journal mic that has .0001 accuracy? Does he do good work?

[Goldenblack440]

thanks for that info, didn't know Fed Mog went to 30. My mechanic doesn't do the machining - he has to get it done as well, and as you might have realised from a previous post, we don't have any really reliable machinists in the whole city. Which is sad. Interesting about that conformability and cushioning. I will cut and paste that info into my accumulating engine theory notes (hope its not Copywrite, Eddie ?!!)