258 Crank Journal Tolerances

[Supercompact]

So, I mic'd all of the journals on a 258 crank I picked up a few days ago. There is no scoring on the journals themselves, but it could use a polish. I read that the main bearing journal diameter is suppose to be No.1 thru 6. 2.4996 to 2.5001 inches and No.7. 2.4980 to 2.4995 inches and the rod journals are suppose to be 2.0934 to 2.0955. These are the measurements I came up with. I measured a stock 242 crank also that I have laying around and came up with roughly the same measurements on the main and rod journals. It looks like both of these are either out of spec or maybe my caliper is not correct, but it hasn't failed me before. I was going to try to go back with factory size bearing because it doesn't appears that the crank needs to be turned. Am I reading something wrong?

Mains
M1 2.496 inches
M2 2.496
M3 2.495
M4 2.496
M5 2.496
M6 2.495
M7 2.494

Rods
R1 2.090
R2 2.090
R3 2.090
R4 2.090
R5 2.090
R6 2.090

[Supercompact]

Another question, can I run the .001 (not .010) bearings in this case with all journals polished?

[Russ Pottenger]

In my opinion I wouldn't put a lot trust in dimensions measured by calipers, and that would include myself.
Only slightly better than using a yardstick.

Buy or borrow a 2 to 3 inch outside micrometer, and a inside dial board gauge.
After measuring your Crankshaft journal with your micrometer, that now will be the standard to zero out
you'r dial bore gauge. With bearings installed and fasteners torqued you'll directly be able to read out bearing clearances.

Standard and .001 under bearings can always be mixed and matched to get the desired clearances.

Hope that helps,
Russ

[Supercompact]

Thanks for the help, Russ! I just bought a 2 - 3 inch micrometer and will pick up a dial bore gauge later. I'll see what the difference is between the two measurements.