Plus 30 bore size
Posted: Tue Apr 08, 2014 7:07 am
Hi folks (and Spider...LOL) would anybody know what the bore measurements should be for a plus 30 rebore on a 1275 Cooper S block please? Thanks. Mark
2.810" would be the nominal bore diameter for 1275 + 0.030", however, for an exact measurement one would normally measure each piston (usually 1/2" up from the bottom of the skirt at 90 degrees to the gudeon pin, however, the piston manufacture will say exactly were the piston dia should be measured) + piston to bore clearance will give you what the bore dia should be.
(hope that makes sense)
Here's one manufacture's info sheet. Note that some pistons are measured just below the lower ring, this is why we need to refer to the manufacturer's advice.
http://www.jepistons.com/PDFs/TechCorne ... rc4032.pdf
edit> here's some Mahle Piston Instructions
