I was being facetious when I wrote that. However, if someone has a 1928 piston with it's 1" gudgeon pin gathering dust it would be very helpful to know its weight since that would let me do better than guess at the original factor balance factor.nevhunter wrote: Doing it to ONE gramme is not really justified, when the factor is an "intelligent " guess.
"Use the figures for the proper one" is the problem. I haven't yet found what those figures are. That's why it would help a lot to know what a '28 piston & pin weigh, even given that there is some amount of variability to the result.nevhunter wrote: I wouldn't balance a motor to a temporary heavy piston (or Pin) Use the figures for the proper one and when you fit it later the motor will be balanced and you don't have to strip it, again.
cmfalco wrote:Gardini +60 7.5:1
P810D-152 on box (only the bore in mm is etched on crown)
Yes, what you wrote is true, but especially important is the "you may get close." I fully realize the uncertainties involved, but I'll get a lot closer -- and, very likely, close enough -- once I know the weight of an original piston. As my previous calculation showed, if I do nothing the range of the resultant balance factor will be a very large ~10% with that range not necessarily even centered on the "correct" value. However, if I know the weight of the original piston assembly to within, say, 20 g this drops the range to ~2% as well as centers it.david.anderson wrote:Even if you can obtain an original piston and gudgeon there is no guarantee that you will be able to correctly calculate the exact design balance factor, although you may get close. There will be differences in weight between individual original pistons and gudgeons, and how accurately were the original flywheels balanced...
Good luck with the hunt for the piston weight.
It should be twice that based only on the increase in annular cross section due to a 0.060" larger OD. However, the ID of the bottom of the skirt of the Gardini is machined so if they kept the lower skirt the same thickness on the oversize piston (i.e. if they also increased the ID of that portion by 0.060") the weight gain only would be due to the extra thickness of the upper part of the piston, reducing the weight gain to the above noted ~30 g.Simon.Gardiner wrote: That would seem to make 30.5g (more than 1oz) weight gain for the full oversize on the same piston.
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