I have scoured the internet and am coming up with very little on this, other than people have had it happen.
I have a Frankenstein trike, Tri Z front end, 225dx frame, and timberwolf 250 engine and rear swing arm.
When I got it last weekend I could hear the timing chain a bit but nothing too loud. All of a sudden it started dying out. It would restart and then die. I didn't want to fry the starter so I started pulling the recoil and all of a sudden it pulled real easy and then seized. What a lovely feeling. Took the top part of the engine and of course, timing chain wasn't on the gear up there. Tore out (gently) the bottom part until I got to the jumbled up chain, as I expected I'd find it.
My thought was that the tensioner failed and the chain jumped off. I was pull starting when this happened, so I'm hopeful nothing in the engine was damaged. What was damaged for sure though was the seat the front chain guide sits in, it was ripped off and laying down in with the chain.
I have a new chain coming, a manual tensioner, and of course a new gasket for the case. Trying to figure out how to fix things so that I can get the front guide to stay put in there.
OR, and here comes the dumb question, with the rear guide and a manual tensioner, can I get away without the front guide?
I've heard two more solid fixes, have the case welded (requires ripping the whole thing apart and bringing it in to a welder) or I read one post that someone mentioned tapping a screw in there but they gave no other info/instructions.
Pic shows the rear guide just sort of laying on the gear, it's fine, and I removed the front guide. You can see the "candy cane" shaped spot that front guide is supposed to sit in, and it's totally gone.