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?

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.

78mm bored early A12 now thats scary :)

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

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

A12A bore is 75mm... so I was right in that 40 thou gives you the A14 bore of 76 :)

Quote:
Any oversize you want. You can order custom pistons from most performance piston manufacturers.

Nissan sells STD, 0.50 and 1.00 (.5 mm and 1 mm oversize).

you can go 74.5mm bore +060(1.5mm)with no problems.i have some new std 040 or 060 pistons/rings if you interested. where r u located. cheers

The A12 is the one I'm referring to.

fredeuce, so are you talking about an A12 or an A12A? Stock bore is different for each.