Here is John Tinley's freshly restored James ML. John tells me that the piston is nipping up. He has given it a skirt clearance of 003" which I would have thought was more than adequate especially with the use of petroil.

John can take up the story. Ron

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email (option): ronpier@talk21.com

I cannot find any reference in the ML manual for recommended piston clearance when being rebored. However, I can find information in the book about ring gaps. I would be really interested to hear what others have to say about piston clearance? Whilst at it I would like to say a very big thank you to Peter Brown who has restored the ML for me and also another big thank you to Steve Madden for providing sparks where I had non. Cheers, Joh

Make sure he uses mineral two stroke oil and not synthetic as most are, despite modern oils being better it's worth using the correct amount instead of cutting down as most people do with the newer oils. Also it's best to run it in down quiet country lanes as they don't like being "pushed along" by modern traffic speeds and the fact that you are varying the speed constantly is good for running them in. The couple of times my flea has nipped up was when I felt I was holding up the traffic and was going flat out. You must remember that they are from another era where 20 mph was adequate, with just short bursts of speed. My Flea has seized a couple of times but I had the head and barrel off the other day and there was just a tiny score on the bore.
Another thing to do is if it has marked the piston, just smooth it out with wet and dry and it shouldn't nip up in the same place again.
The correct size for the piston is the standard bore size plus the oversize that you are on. For example if it says in the data in the manual that it is 55mm bore and you have to fit a+0.020" piston then you simply bore it out another 0.020" from the 55mm (finished size) the pistons are usually a couple of thou undersize from the nominal bore size

email (option): davmax@ntlworld.com

I had the same dilemma when I fitted a new OS piston to my ML. So I phoned up Villiers Services. For the life of me I can't remember what he told me and stupidly I didn't write it down. But I know it was quite a small clearance. I'm sure I read on a piston label to allow 001" clearance per 1" of piston diam.

Might be worth a phone call John. Then you can let me know and I'll jot it down this time......Not that I'm ever likely to wear out an ML piston.

Also the correct fuel/air fuel/oil and ign timing are a factor.

Ron

email (option): ronpier@talk21.com