Screwed up. Help needed for topend rebuild.

[Yamaki]

So my friend made the classic mistake of working on a bike with no sparkplug in (xs500). A small screw from the killswitch ended up falling down the hole without anyone noticing.

Took the top of it yesterday to find this:

Piston took some battle damage as well.

Are these parts salvagable? Can we grind off the damaged parts on piston and topend? The bore doesnt have any scouring or marks.

Also the valves are leaking so they gotta go out, maybe they got bent. Tested with some volatile fluid in the combustion chamber (with the top off the bike) and compression test before dissasembly.

This is my first real topend rebuild so any help and pointers would be much appreciated

 

[Yamaki]

Oh well ill just try it myself then lol

Got the valves out using a diy spring compressor, the valve seats looks dirty and carbonized so we're going to clean it up and lap them.

Hopefully this will do the trick, valves slide freely in the valve guide and i dont have any v-blocks so unless i find another way of testing for trueness, we'll sand/grind off the protruding damage on piston and chamber and put it back together. Fingers crossed.

Still looking for useful tips and pointers if anyone has something clever to add.