Top end rebuild.

[dirtcross1]

Hi there again!!!!
I have got a dilemma.
ok where to start.
I have an Orion Apollo 125 (crf70)
The piston and rings are worn very badly so i am giving it a rebuild.
I got my electronic callipers out and measured the piston and it measured 51.85mm what size piston shall i get and/or what size should it be?
I believe the engine is made by loncin. and loncin engines have 53mm.
HELP!!!!!!!

[josh m c]

Are you sure the loncin measurement of 53mm is not the bore?? Because if its the bore them your piston size sound ok.

[dirtcross1]

I've measured my piston which is actually 51.6mm and the bore measures 52mm with electronic callipers. i don't know whether to go 52mm or 52.4mm as after i hone the bore it might be a little bigger. i think i should go 52mm. lets face it it was 51.6mm warn it had no compression. will the 52mm piston (difference of 0.4mm) make a difference?
thank you for your help