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The piston and cilinder are pretty worn. The clearance between the piston (bottom of skirt) and cylinder (halfway) is about 0,40 mm (total so 0,2 mm all around) and that is quite a lot for a cast iron piston. You can see on the piston that it has been rocking in the cylinder. Arround the piston there is a recess machined in that helps lubricating the bore. The edge of this recess is also worn away completely at the front and rear thus indicating the rocking. And also the engine smoked quite badly as I was told from people riding behind me.

Of course I could re use it and just fit new rings. It is not that I will do hundreds of miles on this machine. But being quite a perfectionist I would like to have things right. And I could have a new piston made (aluminium) for about 150 euros which is a fair price I think.

I also investigated the sleeving option but there is only room to fit a thin sleeve and that will probably deform on pressing in. And of course the cylinder will not be a homogenous part anymore and those sidevalves get very hot so a good heatransfer is important.

To be continued!