Serious engine troubles

[hypophthalmus]

I have opened up the engine. Unfortunately it looks quite bad.

The piston is at an angle inside the block with two valve-shaped indents. The valves also seem to be messed up and not fully seated. The rod seems to be in tact, but disconnected from the piston and bent at the same angle.

The worst part is that the back of the piston shattered, leaving tiny fragments of metal all inside the engine. I think this alone makes the idea of any sort of repair questionable.

So I guess the timing chain skipped.... somehow? Insufficient design? Still not sure why the coolant was a bit low, or why it got hot.

The head gasket looks pristine. I haven't checked anything for flatness.

[CROSSBOLT]

There is not ONE WORD in the DT300i owner's manual about checking or retensioning the timing chain! I recall from my Honda days this being included. Anyone remember the interval?

Yep, the timing chain wore and got slack, timing jumped, valves started touching the piston crown and things got worse real fast! That's my guess on the sequence and I'm sticking to it!

Sorry to hear about the destruction. I KNOW you hoped for a different outcome.

Karl

[hypophthalmus]

Here's my understanding from my recent internet research:

The tensioner is supposed to be automatic. If it develops any slack, the tensioner pushes out more to compensate, but it can't retract.

I came across some motorcycle forums where it was high recommended to replace the automatic tensioner with a manual one, although I don't know if such a thing exists for our bikes. Apparently if the RPM is high, they might not be able "to keep up" (not really sure what that means?). I doubt that

Probably your Honda had a manual tensioner?

I'm supposing it could be a defective tensioner, something going on with the chain guides.  I think I read that a stalled camshaft can also do it. Or a worn chain/gears.

I didn't see any clues as to what actually caused it though.

It's the shattered metal fragments that's really disappointing. Even with the amount of damage, repair is approachable. But don't think I could get out every last bit of metal fragments. And they might have damaged other components at this point already.

I'm not seeing any engines for sale where it wouldn't have to ship from Italy or I wouldn't have to drive to California for. I'm not sure if I should wait and hope that someone has one. Or try to part it out and save up for a new bike.

[hypophthalmus]

Been thinking more about this.

I disassembled the tensioner, and it looks fine to me.

The quality of the oil seems odd. I know I said it seemed normal in the beginning, but I meant it didn't look like it had coolant in it. But has a strange kind of burnt smell and looks unusually dark and possibly thick. Checking how full it was, at first I got nothing. After an odd delay, it went significantly over the gauge (although I'm pretty sure I didn't overfill it).