I have run upto 78mm in a A12 with no problems, so 76mm should be easy.

Thanks guys . All good stuff . Have answered my questions.

78mm bored early A12 now thats scary :)

78 is fine with A12A, but scary with original A12?

If the bore calls for mm, do not let your machinist bore it in inches. I want my engine done not approximately but accurately.

A12: 73mm piston
A12A: 75mm piston
A14/A15: 76 mm piston

It depends on the exact piston size -- via direct measurement -- as to what the machinist should bore the cylinder to:
* 73mm piston has a tolerance of -0.033 mm to +0.017 mm
* cylinder should be finished to a clearance of 0.023 to 0.043 mm.


For 1.0 mm oversize pistons, "0.040 inch over" is not accurate enough (.040" is already a 0.016 mm difference from 1.0 mm). If the machinist does precise conversions that's OK ... but if he talks in inches I would be suspicious. Maybe he'll do it right, maybe not. Does he even know what the Datsun A12 or A14 piston clearances are? Or is he going to use generic clearances?