As others have mentioned, the engine may not be toasted. Verification is necessary.
Before you move to step where you are removing the engine, verify that the engine isn't damaged by putting in a new belt and hand rotating the engine (without the spark plugs).
If you can't, then chances are a valve is broken and jamming a piston - or worse. Damaged pistons will require engine removal.
I've seen a broken valve in a single cylinder dirtbike and valves can embed themselves in both pistons and heads!
If you can rotate the engine, then do a compression test on the cylinders. If one or more are very low or no compression, pull the offending head.
Someone also suggested a borescope to look down and visually look for damage to the piston (Even if the compression is good).
I wouldn't jump to pulling an engine right away is all I'm suggesting.
Before you move to step where you are removing the engine, verify that the engine isn't damaged by putting in a new belt and hand rotating the engine (without the spark plugs).
If you can't, then chances are a valve is broken and jamming a piston - or worse. Damaged pistons will require engine removal.
I've seen a broken valve in a single cylinder dirtbike and valves can embed themselves in both pistons and heads!
If you can rotate the engine, then do a compression test on the cylinders. If one or more are very low or no compression, pull the offending head.
Someone also suggested a borescope to look down and visually look for damage to the piston (Even if the compression is good).
I wouldn't jump to pulling an engine right away is all I'm suggesting.