Topic: 1974 CB500 Possible Frozen Engine

[lakeboi]

Lastly...

[TwoTired]

Look for marks on the cylinder wall, too.

Find the bits of piston where that hole is that are likely in the bottom end somewhere. Hope for a single piece laying in the bottom pan or hanging on to the inside of the piston.

Best case:
New Std size piston and rings.
Hone cylinder
Replace entire head with used cylinder head assembly
New gaskets/seals
Reassemble and run.

Worst case:
Metal bits from hole in piston, valve bits etc. lurking in lower end jam into gears, or something.  Trashing lower end.
Cylinder wall scratched or cracked.
Unavailable std size pistons/ rings.

Other Options:
Swap entire top of motor from a donor engine. (cam. cam cover & bits optional.)  Still need gaskets/ seals)
Swap entire motor. (find a 550, along with the clutch cable and clutch cable engine mount, methinks.)

Bummer...

[merc2dogs]

 That's what I was afraid you'd find in there.
 double check the cylender walls make sure there's no damage to them, 
 If you want to keep the original head, you can normally have new seats installed, and depending on the depth of the gouges in the head either sand them smooth, or have them filled with weld.
 new piston and valve should set you straight after that.
 If you have to buy a new piston, may as well go for all 4 pistons and rebore it to the next oversize.

 Otherwise pick up a known good head and piston and install them

whichever way you go be sure to clean out the oil pan and change filter and oil

  Of course if you can pick up a wrecked bike cheap you could always swap engines, unless you live in a state that keeps track of them.

   Personaly, I'd take the first route with new pistons/gaskets/bearings, it will almost be a new bike.

ken