RM80 Piston to cylinder size

[kprasek]

I have a rm 80 with a cylinder bore of 49.15mm. I was wodering if a 49mm piston will be fine for it. The bikes been honed already so all i need to do is get a piston for it. So will a 49mm be good or will o need a biger piston and hone it again?

 

[helio lucas]

you will need a bigger piston and hone for it... i will doubt any manufacturer make a piston for 49.15 mm cylinder.
check pro-x for oversized in small steps... wiseco have a nice range of pistons also...

0.15 mm clearance between piston and cylinder is too much... most manufacturers recomend something like 0.05mm... check your service manual for proper clearances and specs

 

[JGrossijr]

Pistons are typicaly made for a given bore size. Pistons of different materials and design require different clearances. A wiseco piston that size generally requires .002" clearance. If you put a piston designed for a 49 mm bore in to a cylinder with a 49.15 mm bore you will have aproximately .007" clearance. It will run, but not as good as if the fit was correct, and it will need a rebuild sooner. You will probably hear more piston noise while riding.