i have a 99 blaster bought it last year. i want to put new piston in it but i dont kno how to measure the piston. i kno the guy before me bored it but i dont kno the oversize. how do u measure it then calculate the oversize to purchase the piston. i thought u use a micrometer but how would that work

 

you take a micrometer, move the the measuring points so the flat sides face outward, and measure the diameter of the cylinder. best to measure the top and bottom of the cylinder. since the piston never really touches the bottom of the cylinder that will give the most accurate measurement of what it USE to be. compare it the the measure from the top of the cylinder, if the t measurements are off by a few millimeters, or good% of an inch, then you really need to rebore the cylinder.

but anyway the diameter of the cylinder is what you want. then compare it to diameter of stock cylinder: 57mm stock bore i think

 

thanks cherokee u help me twice lol i knew a micrometer came in somewhere, i did a rebuild on my honda and i new it was stock everything so i didnt measure, but thanks again

 

I just look at the number stamped on the piston top. You can stick a feeler gauge between the piston and the bore to see what oversize to get.
Piston + feeler gauge + .010 to clean up the bore...........order that piston.