Hi,

the valves hit the piston in this engine and mashed things up. There are two bumps on the cylinder's top as a result one is .17mm and the other is .09mm. Is it possible to hand sand or machine grind these down?

http://s10.postimg.org/muepud0u1/20160305_111930.jpg
http://s16.postimg.org/tnlvhy7ad/20160305_111949.jpg
http://s7.postimg.org/cf1vyjonv/20160305_111958.jpg

I would dress it up using a small round file then finish with a piece of emery cloth.

There should be still plenty of cylinder wall material left for the gasket to seal on since the bump is mostly confined to the inner 1-2mm of it.

Yeah there should be.

I wouldn't use a file though, just very carefully and slowly wet and dry the bump out by hand.

This is what we do when removing nicks from compressor blades in jet engines, it keeps the strength in the part by removing the defect and taking away absolute minimal material.

What sanding compound/ emery cloth grade can I use and how can I protect the piston and cylinder wall from contamination by sanding compound and dust, since they won't be coming out?

I have used a file when been in this situation before,
There are cutouts in the cylinder for valve clearance as standard,the rings don't get anywhere near this point, now when I say file i use a very small round or half round (needle)file then finish with emery.

Thanks! Will post dyno charts when I'm done.