good chance it will be piston slap or like the other bloke says main bearings all depending what sort of noise and what engine speed it makes it ,if its all the time and sounds hissy its the mains and if its like a rattle on the overun (when the engine is slowing down after revving up) also could be a big end or small end bearing knocking small end sounds similar to the piston slap and big end is very loud knocking especially under load ok from adam mr 2 stroke
adam, December 2005
