If it is piston slap then it needs to be sorted asap,a loose piston will crack at the skirt and end up in the bottom end.not to mention it will scrape the nikasil plate which is over £100 to fix,Also it is very hard to determine just by listening to it,it may well be the lower rod bearing about to explode in which case it will again take out the top end.The only way is to strip the top end and check for any wear and check to see if there is any up or down play on the rod,if there is play on the rod it needs to be rebuilt.I have had 2 strokes for over 25years and race motox,i also rebuild them as a hobby
mikec
April 2010
it will more than likely be piston slap,does it make a rattling noise on the overun around 3-4 000 rpm ?these have a nikasil plated barrel ,i would not worry about it if its slap as it will just save you from seizing it up unless its really bad and if it is then put a new graded piston kit in it.
adam bike doctor
April 2010
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