OEM Piston sizing question

[Pincushion]

My 03 is in dire needs of a top end job. The previous owner told me the motor still had the stock pistons in it, which may or may not be true. I tore the motor down and they are cast pistons with no markings to indicate they are oversized, but they measure exactly 64.50mm on my calipers. That's .020" over, right?

 

Would OEM .020 over pistons have any kind of markings on them to indicate they're oversize?

 

Thanks!

[deckheight]

Anywhere close to 64.5mm would be .5mm over. It's hard to see some times with all the carbon and junk, but there should have a 5 somewhere near the center.

[kawiking]

id have the cylns miced...

 

64.00 is stock piston.. and goes up .25

 

http://www.wiseco.com/PDFs/Catalogs/CB07/YamahaATV.pdf

[Pincushion]

I dont see any number stamped on the crown, but there is a 'G' stamped on there. As well as the arrow indicating exhaust port direction. I sanded the carbon off to verify.

 

I went to sears and 'borrowed' some calipers. 64.5.. on the nose! Measured in multiple spots on the piston. It's possible the calipers are off, but by a 1/2 mm is doubtful.

 

 

Thanks for the replies. I'll have the jugs miced rather than play the guessing game.

[deckheight]

Wise choice, not something to screw around with... Harbor Freight has their "El Cheapo digital calipers on sale for $17 or something. Decent calipers for the $$$ if you take the time to search thru them for a good one. Might have to "test drive" 5 or 6 before you find a good one LOL!