Wouldn't that leave some "forensic evidence" Iike scratched block or messed up plug threads?
OOOHHHH wait! Clothes line or soft rope in the cylinder, through the plug hole, and a big long breaker bar on the flywheel nut might do that.
That looks like EXHAUST valve that is bent. I do not think water did that. Even if a small nut or washer got that far, the spring is not strong enough to bend the valve. Something would have to be holding the valve closed while the cam was pushing it up. What does the head look like?
That gave me an idea.
If I MAKE a muffler and send it to you, will you screw it on that trike and let us know about the noise and performance?
I put one on a generator about 20 years ago and it ran fine. The only noise I heard was the piston slapping around.
Was not my generator, I built it for...
Not bearing inside engine. It was still running when the chain came off, right? look at chain tensioner/ Does it have a jackshaft? Is there a big plastic cover on the left side? Remove it and see what happened.