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A12 Crankshaft pilot hole bore dimm's

Subject: A12 Crankshaft pilot hole bore dimm's
by edp on 2021/10/26 3:23:10

Hi All - been awhile since Ive been on here, finally getting back to my coupe project. Started resurrecting an A12 to replace my A15 which keeps eating cams (giving up on solving it....for now at least) A12 was a built race motor which I wor4ked over about 2 years ago, figured out all the valve clearance issues, chamber volumes, has aria forged pistons, worked head and a highly polished crank.

I pulled the pilot bushing out of the crank, measured the ID of the crank bore & its .653, the OD on the bushing I took out is .652, I'd bought a Velao clutch kit awhile back & the bushing that came with it is a National PB-21, it measures .670 OD so Im not cramming a .017 over bush into the crank - what gives??

are there different cranks with different bores? all the bushings I find available are for the .670 OD, I'm going to go measure another A12 bore & see what it says.

I thought all A series cranks were identical save for the stroke, could it be a really early one or possibly from an A10?

any thoughts how to resolve it, havent found a bushing thats .652 available yet...