I'm guessing the edges around the valve reliefs?

what grit sandpaper? wet sand?

 

?

 

on that piston there really isnt any sharp edges. looks good to me , but what do i know .

 

I believe its the "sharp" edges that you seen arounfd the valve relief area...As far as grit/ wet sand, I think people have been doing this with scuff pads...You can use one of the rougher grits...Also try theoldone.com, they may have more info on this....HTH....

 

I used to do that with my 2strokes engine,

with 2000 wet sanding paper,
VERY LIGHT sanding around the piston top itself and a bit on the valves relief edge that's all sanding the pistons should not take more than 1 minute per piston. Be carefull not to touche the ring land and wash them perfect after you done this, wash with part's cleaner.

that's the way I did this on my dirt bike, but I never done it to 4 strokes engine.
I guess it's absolutly the same way caust it's the same metal for the piston and it's also the same purpose ( to reduce risk of detonation)

I Hope this help
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