Piston identification question

[flintcam]

I recently acquired two identical 1960s Mercruiser 120 HP engines, on one the pistons are stamped "00" on the other engine the pistons are stamped "30". I am wondering if anyone knows why they would be different?

 

[achris]

Re: Piston identification question

"00" = Standard size
"30" = 30 thou oversize (0.030")

 

[flintcam]

Re: Piston identification question

Thank you for the answer. I was wondering why such an old engine held air on a leak down test, now I know, thanks again.