I’ve been recommissioning a 2004 Rev 3 and although it appears runs ok (on the flat, yet to try on the hills) my Rev 3 appears to have a bit of a piston knock at all revs. I’ve taken off the head and although a bit coked up the piston and cylinder bore looks in good condition. Whilst there is no detectable play vertically, I’d estimate 1mm play fore and aft and side to side for the piston in the bore. The piston is stamped 72.457 (04-14 8724) and I wouldn’t be surprised if this is the original piston but can’t find the exact measurements for the pistons or oversize replacements if anyone has these please?

Is the lateral play acceptable or does this point to cylinder/ring wear and or the small end bearing etc? What would be the best course of action to refresh the engine, new rings, an oversize piston kit or cylinder re-plate and new matched piston etc?

I’m new to 2 stokes so any advice greatly appreciated!

 

cheers jon

 

Something fishy here I think. I can't see it ever getting to that much clearence, it should be more like 0.10. If it has worn it's way through the very thin coating on the aluminium bore then yes, rapid wear will occur but normally they seize up.  The pistons come in a range of sizes but only fractionally apart as manufacturers find it easier to match a piston to a bore already produced.