Before you worry about a piston , have you checked for any other damage such as a bent con rod or valves ? Hi, so sorry for the late reply, yea it's only the piston and rings which are now in the engine and the head rebuilt. Con rod fine, valves were fine the only problem I ran into but sorted it in the end but still don't know if it's right? the problem I speak about is after sorting everything I couldn't get the cam chain to go around the cam sprocket without lifting the back end of the cam out of its housing to put the chain on but then had to use the top of the head to force it back into its housing when it got blotted back down. I've since learned that the chain tensioner has to be completely out to allow the chain to go around the cam sprocket. The timming order is what's really on my mind now as the only info I could find on timming up one of these engines is to have the F on the fly wheel but there is also a T on the fly wheel to which I set it in the end" T top dead and then again F fire lol the cam sprocket got 2 lines which are flush to the cylinder head and put everything back together after turning the engine a few times through a 14m socket on the fly wheel and it turned free so I'm hoping once it's back in the bike it will fire straight up?