Panhard pistons are quite heavy and bulky items compared to their modern day equivalents, because the piston has to be domed to make the compression high enough within the hemispherical combustion chamber in the Panhard engine.



The biggest limiting factor is the close proximity of the top ring to the end of the steel liner, and because the top ring is quite far down the piston, around 10mm from the top deck, this really limits what pistons you can use. BMW R80 non Nicasil, circa 1980’s, can be used, but they are very scarce, as most people fit the 1000cc conversion kits, as they are cheaper. You can also get a piston from Peter Breed, which is a forged American item. Others that can be used are various Italian, German, American & British designs, but nearly all require a little rework to the cylinders to overcome the cylinder liner problem.

What do the standard pistons look like? Here’s the troublesome liner position, and it’s about 1.5mm from the top ring…this pic is taken from a cutaway section.



These engines were from the junk pile, but they still have their uses, as the piston below was cut up to show the typical cross-sectional areas that exist within the original. There are more than one type of Panhard piston used in the flat twin engine, but this is the later 4 ringed type.







Why is this done? I need to understand why the naked Panhard piston weighs 505 grams, when my achievable target weight for a heavily domed piston should be sub 400grams, which for example is double the weight of a single cylinder Supermotard piston from 2002, and probably three times heavier than a complete MotoGP piston! However, pistons that light do have very short maintenance cycles, which are measured in hours not years.