Piston advice please

[stumpy]

Hi i have a gp 150 engine but what size in mm would it be please ?And would there be a alternative to lamby piston that would fit ?
Cheers Andy

[Andy Pickering]

You are better off taking it somewhere if you cant measure it yourself Andy, it could have had re-bores and the best you will get would be a total guess TBH.. if its not the original bore

[Muppet]

my sx was 57mm new but it has been rebored at some time; I was looking for a better quality piston to put in it but had no luck

[goldeneye]

you can get a standard GP150 top end for not much more than a piston and a re-bore, probably cheaper. standard was 57mm i think . as Lam46 says , could be any size. i"d buy a new top end, or get yours bored to 175 and a new cylinder head for not a lot more.

[stumpy]

so what cc does the head need to be replaced ? and how big can you go on the barrel before machineing is needed on the case?
Cheers for the advice on the piston :bigsm: