Re: Need help on old mercury.
Are the pistons in your engine or are we talking about the pistons them self ??
If they are inside the engine... you will probably need pull them out....
If you only got the pistons and are wondering.... there should be some numbers ontop of the pistons.....
Standard pistons might say STD or just nothing
.015 are .015" over STD
.030 are .030" over STD
( Mercury, Sierra, ProMarine, Persan... )
If you find 020 or 040 they are probably Wiseco pistons ( should be other numbers too )
And at the end... STD = 2-7/8" = 2.875"
Arne Kjetil