Pitting on the Head on my Rotax 657? Still trying to figure out Hydro Lock....

[randomguy]

Hey guys:

Got my PTO gear off tonight. Did a complete tear down and clean up on my engine after getting the crank out. Yes the mag side rod is good and bent.

I'm still thinking that I'm going to order a rebuilt crank and reassemble it myself, but I'm still trying to figure out what happened in the first place to bend the arm.

What intrigues me now is the pitting on the underside of the head. What do you guys think about this? The engine wouldn't turn over because the rod was bent and locking up within the crank itself, so I know there were shavings on the bottom side of the rings. But the walls aren't scored at all, and the cylinders and rings look good.

This engine has already been rebuilt. Think these are just old wounds? They seem pretty well smooth, there's nothing embedded in them, and there weren't any shavings or anything in the chamber when I disassembled. Thoughts?

 

[Dr Honda]

The head looks like old damage. It should be fine.

Now... bending a rod in one of these engines, without a "Melt-down" is not any easy thing to do. BUT... if the crank was the original crank, and there was a top-end failure before... the rod could have been bent from that. (But not enough to keep it from running) Once the engine was put back together... the rod continued to bend, until the new failure happened.

 

[randomguy]

Interesting thought. Are there any markings put on the cranks when they're rebuilt? The pistons are marked with the 050 marking that seems pretty standard, but it could have just been a top end rebuild. Again, I don't really care, I just want to make sure that if this happened because of something I did that I don't do it again, obviously.

Seems like the conventional theory has to do with freezing, but how would water have gotten in the combustion chamber in the first place? I can't find any cracks or leak paths. I don't think it cranked over enough times to have gotten the required amount of unignited fuel in there to have become locked up that way. So the slowly-bending-over-time theory seems to make sense, except that I drove it right on the trailer in September and no worky in June.

So it seems like I should fill the water jacket with antifreeze next winter. Should I just run this into the flush port on the head? Do you need to find a way to propel it, or just let gravity run it in?

The head looks like old damage. It should be fine.

Now... bending a rod in one of these engines, without a "Melt-down" is not any easy thing to do. BUT... if the crank was the original crank, and there was a top-end failure before... the rod could have been bent from that. (But not enough to keep it from running) Once the engine was put back together... the rod continued to bend, until the new failure happened.