[olddog]

Describe electrode collapsed a little better.
Is there parts, missing from the plug?
Does the plug look like it has been hit or stuck by something?

There is really nothing to explode technically. Look over the carburetors, for a missing throttle plate or choke plate screw. I tiny piece of metal can just about beat the inside of a cylinder head and piston to death. If a valve head popped off I would expect more damage. It may just be a plug failure, but you have to make certain that ALL of the pieces are out of there!

Do you have a friend that has access to a fiber optic camera? Sure would be nice to see what the inside looks like. If you pull the intake you can look in the intake valve and see a little bit, but not enough to be certain.

PS
Sorry about the redundancy I didn't see Lineslinger's post.
I typed this and clicked save. Took a ride and came back, and it still wasn't saved. Clicked save again.