Auburn 680 Engine Dimensions

Thank you Ivor!

Yes you are correct,
The nominal cylinder bore is 2.875" Lycoming would have had a machining tolerance on this like 2.875" +0.001" - 0.000 and the invar strut pistons would be machined to have the correct clearance of 0.0015" to 0.002" when measured at right angle to the piston pin just up from the bottom of the skirt and checked with a 0.0015" x 1/4" wide shim in the bore. For the main bearings the nominal diameter is 2.375" and the con rod 2.125" the crank journals would be ground to give the correct clearance of 0.0015" to 0.002".

I have some questions about my Auburn 680 dimensions with answers that should be very obvious, but I'm being cautious. I want to verify the STANDARD nominal dimensions for cylinder bore, connecting rod bearings and crankshaft main bearings. My Instruction Manual bought from the museum lists these dimensions in fractions. I just want to make sure I should just simply convert these to their respective decimal equivalents (meaning these are not some oddball dimension rounded to the nearest fraction).

In other words:

Bore: 2-7/8" is its equivalent 2.875" (meaning it's not 2.870" or something else rounded up)
Connecting Rod Bearings diameter: 2-1/8" is its equivalent 2.125"
Crankshaft Main Bearings diameter: 2-3/8" is its equivalent 2.375"

Is this all correct?

Thanks