What could have done this?

You can feel the grooves

All the bearings have about 250 miles on them. They all look like this (main and rod). Except the top halves which look like...

this. O.K. bad picture, but no copper.

Here is my cam. If you look close you can see a chip out of the left side of the lobe.

Here is the cam bearing. They all look as good as this one.

Here is the rear main bearing. You can see the 2 notches worn into it by...

these. The little nubs sticking out.

And now for the worst...Notice anything missing?

How about this.

What the hell could have done all this?

 

Damn!!, looks like the material from that dropped piston skirt got into your bearings. It will tear them up real easy, as your motor is proof.

 

I couldn't agree more. Although I'm not sure what caused the piston failure, the only time Ive ever had a piston shatter was in my brothers old Honda dirtbike.

I hope you get her running soon!

 

Those notches in the rear main bearing are there from the factory. The crank didn't grind them. They help guide the oil that is leaving the bearings to leave in those places. It looks like a chunk of "something" got loose in there, but I can't tell if the broken piston skirt is the cause or one of the effects.

The crank and bearings look like they have seen metal shavings of some type. This once happened to me, I used a "Ball hone" to clean up the cylinders and didn't get the bores clean. The metal "ate" the crank in about 25 minutes of run time. If there is less metal (than I had) it would take longer to do the same thing. What was done to the motor when it was rebuilt? (honing, rings, bore, new pistons, etc?).