96XP 787 Engine Failure

[JeremyD615]

Well I had a rough day on the water yesterday... I got the Speedster and both XP’s out on the lake, and about halfway through the day the 96XP seemed to give up the ghost... My brother was riding it at the time, and he said it started bogging a bit before it started making a metallic clanging noise. Sure enough, I hit the start button and it sounded like a can full of marbles, although it did start and run...

After we towed the ski back and got it on the trailer, I fired it up again outside of the water and it took some throttle, but it did start and even idle for a few seconds. From the sound of it, I thought for sure that I was going to see all kinds of carnage when I pulled the head off, but when I pulled it this morning I was surprised to see that it appears to all be in one piece.

The motor turns freely by hand, the plugs were on the rich side, but there was no mechanical damage to them, and if I crank the starter with the head off, it sounds pretty normal. Internally, the motor definitely has some wear on it, but the pistons are tight and don’t have any obvious damage. The cylinder walls are far from perfect, but I don’t see any scarring or scratches.

Here’s the mag piston and cylinder.


And here’s the PTO side.


And here is a link to a video of it cranking with everything removed.

Anybody have any ideas? I think I’m going to have to pull the motor, as it definitely sounds trashed when it’s all put together. I just would have thought there would be carnage everywhere, and I’m not seeing it or hearing it until I put the head back on it.

 

[racerxxx]

Look in the back near the pto as sitting on the ski. To the left there the back bolt on the pipe. Can you see inside the crankcase? Wondering in the counter balance shaft rear bearing gave up the ghost. Original bottom end?

 

[JeremyD615]

I believe it’s the original bottom end, but this ski was a restoration that started out in pretty rough shape, so there’s no telling what’s been done over the years. It looks like it’s original though. I can’t see in the crankcase at this point, but I’m probably going to just pull the cylinders off so that I can dig into it.

 

[JeremyD615]

Well I pulled the top end and got enough stuff out of the way to see the back side of the case, and I found a crack in the block at the balance shaft cavity. There’s some water in the crank case as well, so I’m thinking that it was somehow ingesting water and it got into the balance shaft cavity. I’m not real sure how that’s possible, but something definitely let loose to cause the crack and the horrendous sound it was making, and there’s a fair amount of water sitting in the bottom of the case. There’s got to be a correlation between the two... I did have to tow the ski about half a mile to get it back to shore, but we pulled it slow enough that it took a good 15-20 minutes to go that half mile, so I don’t think the water came from the tow...

The strange part is that the pistons don’t look steam cleaned, and the motor still turns smooth by hand... Either way, I’m going to have to find a good used motor or at least buy a salvageable case to use as a core. I’d just like to figure out where the failure was before I put a new motor in it...

 

[mikidymac]

Balancer shafts are known to blow out cases.

Nick and Jess at Westside Powersports can set you up with nice used cases.
SBT sells Balance shafts if you don't want to rebuild it yourself and OEM cranks are $375 direct from Seadoo.

421000076
REBUILD-CRANKSHAFT 787 96
This part replaces 290887313.
MSRP: $438.99
Dealer Price: $373.14

 

[JeremyD615]

I appreciate that. I’ve got to clean some space off on my workbench before I yank the bottom end out of the ski. I’ll give Nick or Jess a call as soon as I figure out what all I actually need...