787 seized up - looking for possible reasons 1996 Challenger twin rotax

[jimd]

Just rebuilt the cards on both engines and everything was working fine.
This engine was rebuilt last year 2010 by a reputable dealer but seized again 2011 - looking for reasons why this would happen. Here is the problem trail.
Used the boat for hours last week skiing & tubing. At end of the day starboard engine stopped. Look at engine and the exhaust hose had a hole in it. I look further and the water regulator valve on the exhaust resonator has blown off the top. I limp in on one engine after clamping the water intake. I replace the hose and regulator valve with a new valve. Runs great on trailer and runs great in no wake zone. I get to 3/4 throttle and the engine RPM's go to zero and will not start. I limp in to the dock let it cool and will still not crank - so I guess I have a seized engine again!!

Any suggestions as to the cause? Thinking this engine is got the plague?

 

[BEA5T5IDE]

does the engine move when cranked or is it lokd up???

 

[bigJake]

Just rebuilt the cards on both engines and everything was working fine.
This engine was rebuilt last year 2010 by a reputable dealer but seized again 2011 - looking for reasons why this would happen. Here is the problem trail.
Used the boat for hours last week skiing & tubing. At end of the day starboard engine stopped. Look at engine and the exhaust hose had a hole in it. I look further and the water regulator valve on the exhaust resonator has blown off the top. I limp in on one engine after clamping the water intake. I replace the hose and regulator valve with a new valve. Runs great on trailer and runs great in no wake zone. I get to 3/4 throttle and the engine RPM's go to zero and will not start. I limp in to the dock let it cool and will still not crank - so I guess I have a seized engine again!!

Any suggestions as to the cause? QUOTE]

well if I had to guess as to cause I'd go with what you said "This engine was rebuilt last year 2010 by a reputable dealer". If the engine was rebuilt last year because it seized, it sounds like they got it running again but didn't bother to find or fix the root cause. But that's just my guess. I'd start with why did the water regulator melt down. sounds like something might be clogged in the cooling system

 

[jimd]

I pulled the engine apart and one of the bearing on the crank shaft is shot. Seems that the oil resevoir had a hugh crack in it so probably the lower end was starving for oil or the oil was compromised. Since the 1800 is a twin engine machine, I feel fortunate I only lost one engine.
Wish me luck with older engine! I just finished replacing the blown engine wiht a new Rotax 787. I had my second test run this weekend just in time for the season end. I am all ready to go for next summer.

 

[Seadoobuddy]

Good luck! !
From where did you get the new 787?