Originally Posted by keavze
stefan: i'm using the sleeve shim from my old tuned nosram.12
did an engine cleanup and observed the following (see pic).
time to ditch the engine? or replace new P/S and button?
caused by over-lean? i suspect caused by foreign debris...
This was caused by debris (plug coil?) not detonation. Detonation is finer and more equally spread over the entire piston.
I had that as well, no need to change the parts. If you want to, you can use some 1500 sandpaper and carefully sand the top of the piston and the button.
Place the sand paper on a flat glas surface (mirror) and slightly rub the piston over it with equal pressure. Don't over do it.
You can put the button with an old plug mounted in a drill, run it at low speed and hold the sandpaper against the pitted surface.
You don't have to sand it completely smooth, just take the coarse stuff off.
You might wanna check your rear bearing as well for missing balls or part of a ball.