Oil baffles and modern piston's

[Tony Betts]

You cannot base rebore sizes on a digital calliper measurement. You need a decent Mercer type bore gauge. Taper & ovality needs to be assessed to know the minimum size that it'll clean up to.
Find your machinist (by recommendation ideally) and take them your block. Get them to measure and assess it and then buy the pistons. Bear in mind that some pistons (such as Tony Betts') are sized in metric which can be a useful size between standard 10 thou steps.

thanks charles, you mainly covered what i was about to say.

the reson you get a lip at the top of the cylinder is because thats were the rings stop, also the rings will not reach the bottom of the cylinders. this means useing a vernier is totally useless. as charles suggests you need to measure the used bore for wear and ovality, and what most people miss is if the last rebore was machined off centre, you may have to coorect it.

i would advise anyone looking to rebore, check with all supplier first for the sizes of pistons they have in stock? not being cheap to put on the shelf suppliers often run out of a couple of sizes before they restock. so no point in boreing to +60 if they are not available.

also as suggested by charles metric pistons work out at roughly +4 thou over metric. ie +80 imperial works as +84 or 58mm metric

also know what talerances the each piston type needs in the bore.

then you can get it machined to correct size, and burn less oil.

tony