Without knowing too much specifically of the gs motor, I am very familiar with BMW engines and it is not uncommon for the pistons to be the first to go and the cylinders and rest of the engine to look fine. Unlike most other engine the cylinder walls in BMW's are nikasil coated or treated. The makes them the metal equivalent to diamond. Pistons wear and the cylinder remains. Nice in a lot of ways since you don't have to overbite when you rebuild. New piston, new rings and a go. It is a little odd for the pistons to wear but something has to give no its not the wall, then....... Good luck. Pictures would be great :)
Since you are familiar with the BMW engines, do you have an idea of how much this is worth $$$ (getting new pistons etc?
Couldn't tell you as new these. Can't image more than a few hundred for parts. Mostly just labour I would image and motorad seems to be creative and a little lazy with their hours. Let me know when you find out. At the rate I ride I'm sure there will be one of these repairs in my future
Looks ok to me. Pistons are not cheap but normal for OEM, labor seems reasonable for the amount of work it will be.
Seems there should be some higher quality, higher compression, lighter, and cheaper aftermarket pistons available. Since I'm hopefully about 100000miles away from needing them, I haven't done a search to see what is available.
Rebore, get the bores nikasil treated, and fit some Husky Nuda pistons. I think they also stroked it a little to get the 900cc out of the Nuda, but you'd be part way there. Maybe. If they fit.
Nikasil plated cylinders can wear as well, so you should still get the cylinders checked with a bore gauge for taper and out-of-round.
my piston on the left. The darker body means that it's teflon-coated, they say. carbon + my sexy hand
There are a few pistons like that are out there, you get any insight about about yours. You aren't one of those, it runs fine on regular guys are you? Any modifications you don't want to tell us?
The gunk ( Carbon ) on the top is normal, due to all the different additives in modern gas. You do however have quite a lot of blow by. ( rings not holding back the pressure) Which is then caking the oil channel in the lube ring...which then further decimates the lube process. This much blow by would have been visible in the exhaust, I would think. Did you notice any " abnormal engine behavior"....or did you just decide to tear into the motor for the fun of it....????
