Trev -
Maybe I was just unlucky enough to get a foul set of GPMs and the majority is ok, but the set I bought for the A10 had a wrong shape. Although the skirt diameter was right, both didn't have the barrel-like shape a piston usually should have, but were more or less just tapered. One of them even was hollow on one side, a fact I unfortunately didn't realize before fitting them.
I hope you know what I mean. Usually it should look like this: (_)
One of mine looked kind like that: (_(
exaggeratedly drawn
Well, as fortune would have it, this hollow side came to be fitted on the exhaust side of the LHS cylinder. When a piston shaped like that expands when warm, it naturally cuts of oil supply to the sliding surface between cylinder wall and skirt and it seized after the first few miles of serious riding, once the engine really got hot.
As you will probably know, GPMs come from Italy, and having talked to some people from this scene, they are also well.known for seizures and broken skirts in the Vespas and Lambrettas for which they produce pattern pistons, too.
A long story short: I personally will not use GPMs again and will not recommend them to anybody else. I made good experiences with the JPs in the A7 before I found the Wisecos. They are significantly more expensive, but you can literally see the difference in quality and accuracy.
Oh yes, I used a clearance of 0,12mm (0.00472 inch) on the GPMs, which should be enough considering the fact that they recommend 0,10mm
