Andrew, thanks for your thoughts on this issue, the little bits of metal that I did find on removal of the head were tiny flakes, ie, flat in shape and very small, like a grain of salt size but flat. And with ref: to what Steve mentioned, I took the back plate off and found some scrape marks on the plate. Now, I've never stripped an engine before, Been model flying 5 years now, and this will be my first strip! Woo Hoo! I'm eager to do this perhaps with a few pointers from you chaps on here as I go along... I will have the crank pin looked at by someone in my club, but a strip down and clean sounds like a 'must'. I hope to start this at the weekend ( I also have a septic tank to pressure wash but thats another story!) but will come back here, if thats ok, when I need advice. The first thing that has me puzzled is how do I remove the piston? By the way, this was a 'Blackhead' but the enamel is long gone, The head fins are finished off square as opposed to being slightly rounded off as with the earlier? orange head. I'm also having a new venturi and nva made as this engine is an r/c type. I would like to save this motor as Its seems perfect in my Flite Streak (when its not burning plugs). I have a feeling 'I'll be back' to coin an Arnie phrase.. Thanks Phil