Singles pistons

Just to add to this, I have seen reference to how heavy GPM pistons are so I weighed mine, and a hepolite. Both were including rings and gudgeon pin. GPM weighs 569 grams, Hepolite 480 grams. The GPM pin on its own is 29 grams heavier than the hepolite one. So if anyone fits a GPM piston without also rebalancing the crank, don't be surprised about the chronic vibration! (I admit that the GPM was +60 and the hepolite +30, but 89 grams.....! )

Previously wrote:

Hi

Has anyone had excessive noise from the use of a GPM piston? My 1950 Big 4 has a +60 barrel with a matching GPM piston. It has been rattling badly and after a long story involving replacing the rings (original gaps were in excess of 70 thou) with new correctly-gapped GPM rings I have measured the piston clearance to be 12 thou. The Garrett manual says that the wear limit is 6 thou over the standard 7 thou (ie 13 in total) so my 12 is close to the limit. But I wouldn't expect such a clatter even so. Its had a new big end in recently and the little end is fine. I wonder if the expansion coefficient of the GPM is less than a hepolite so 12 thou is actually quite a lot when hot. Any ideas? I'm going to swap barrels for another +30 that I have and put in a NOS hepolite.