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Author Topic:   Bearing Clearances
posted July 28, 2003 11:16 PM
the only way to be sure is to mic the bearings torqued in the mains and rods and then mic the crankshaft journals. it takes a while, but you will know exactly. i had to use a half a set of +.001 oversize rod bearings on my new crank to get the clearances right.

posted July 29, 2003 07:47 PM
There are many opinions and publications on this subject but I think the goal to shoot for is .002 to .003 clearance - correct me if I'm wrong guys! We've ran them as tight as .0015 and had problems. And yes - install the caps with bearings and mic the I.D. - I'd also recommend to mic each journal on the crank shaft - We've also found out the hard way that "plastaguage" is not good enough - once bitten - twice shy!

posted July 30, 2003 01:09 AM
.0025-.003 on the mains and .0015-.002 on the rods. these are the numbers i shoot for.

posted July 30, 2003 01:53 PM
.002" is about the minimum I like to see when using race bearings. Mains can be up to .003" if using a HV pump, rods up to .0025". Federal Mogul makes odd size bearings, .011" and .021" to get the clearances down on rebuilds. That way a crank can be polished to the small side of the spec and not have to be reground. I think they also make .009" and .019" HP bearings too.

So it's a combination. You need to know the exact size of the crank and exact size of the bearings in the cap to get the clearance right. Polish the crank a little smaller or get different bearings to get at least .002" clearance.

posted August 03, 2003 07:31 AM
My mistakes in the past have taught me the following: ALWAYS make sure the machinist that is actually doing the work, knows that the piece is a race part and the specific clearances you want. NEVER make the measurements with more than one gauge. Example: you measure the rod journal O.D. and then want the rods resized to a certain dimension. You used your gauge, but the machine shop will use another. BIG PROBLEM

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