Piston failure and debris in the crankcase.

[waltersbg]

The 787 engine in my 1997 GTX stopped turning over a while back. I initially suspected the battery, which turned out to be good. Then I hoped it was the battery cables, which turned out to be good. Then I hoped it was the starter, which turned out to be good. Finally I realized that the engine simply could not turn over. Something was preventing the drive shaft from turning and it was not debris in the impeller. Here is a YouTube video showing the problem:

https://www.youtube.com/watch?v=7HlkzUwkGFY

I finally faced the fact that I needed to take the engine apart to find the cause of the problem. I'm very inexperienced in any kind of engine work but with the help of the Shop Manual and plenty of time I finally got to the point that the cylinders were removed. What I saw was not good. Not good at all:



Here's a closeup of the broken piston:



So, there you go. That piston has broken and the "missing" pieces are down in the crankcase and preventing things from turning.

My question for the group is what is the most likely cause of this? Obviously a lack of lubrication? Could that have come from one carb being plugged? Is there a clue in the difference in color between the two pistons? The right one is dark and sooty. The left one is clean/white. Could the left one have been running lean or perhaps getting no fuel/oil at all?

Thanks,
Mike

 

[Dr Honda]

1) The rings were shot, and the pistons were already trying to seize. (lightly sticking them)

2) Looks like, at one time... the engine had some nasty rust in it from sitting. (I can see the port print on the pistons)


3) Between the two... that allowed a lot of heat, and piston slap. In turn... you cracked off the skirt.

 

[waltersbg]

Thank You, Dr., for the quick reply.

I did just about everything wrong that could be done wrong with this (my first jet ski) and so I'm willing to take all the blame for this failure. But I hope to figure out what parts failed so that I can prevent it from happening after I repair/replace the engine core.

First of all, since I believed this jet ski had always been used with non-ethanol fuel, I did not replace the grey fuel lines when I bought this used (and continued to use non-ethanol fuel). Secondly, my version of "winterizing" was to start the engine once per month during the off season. Thirdly, when I started the engine once per month I did so out of the water. I only let it run for about 45 seconds when doing this and I thought this would be OK. Lastly, although it is debatable whether this was really a bad thing to do or not, I stuck with the oil injection instead of changing to premix.

So, with all those things combined, there was plenty of opportunity for heat and/or rust and/or clogged carburetors and/or failed lubrication. Now I'm just trying to figure out what to repair/replace (in addition to doing things differently in the future).

How did you know the rings failed? Was that just based on the end result or can you see it in the pictures? Unless the ring was clearly cracked or broken, I'm not sure I would know a failed ring from a good ring.

Is the difference in color between the two pistons an indicator of anything?

I'm not exactly clear on where water is designed to go in the engine and where it might be by happenstance and/or condensation. I didn't expect there to be water in the cylinders (and therefore didn't expect rust). I do see the glimmer of what looks like a little bit of water in the bottom of the crankcase and I wasn't sure if that spilled there from the cylinder head when I took everything apart or if that water is another indication of some failure.

I'm not sure what kind of damage might be been done inside the crankcase. The strange thing is that the engine actually started one time after it first had trouble turning over. I thought the problem was the battery when it first failed to crank, so I charged the battery and was able to start it. I'm thinking that it must have run with the piston skirt already shattered. Yikes.

Would more pictures of anything help?

Honestly, I'm not sure I want to put the money into this to fix it. We use this jet ski inside a "Shuttle Craft" boat hull and that means we use it a lot like a boat. If we try to head up river in our local lake in the 5MPH zone or if we sit and idle for a couple of minute while a water skier gets ready behind us, we foul the plugs. We really like having both the "boat" and the jet ski that we can take out and bomb around in, but I think a 4-stroke jet ski would be better in many ways. Unfortunately, the fiberglass rails that hold the jet ski in the hull are custom to particular jet ski body styles and I have the rails that pretty much work with the 1997-1998 or 1999 Seadoos GTX style. The company that made these boat hulls is long out of business and to get new fiberglass rails for a newer 4-stroke jet ski, if possible at all, is exceedingly expensive as the owner of the molds (last I heard) is in Australia. So, I'm thinking of just selling the whole setup rather than putting the money in to fixing this old jet ski.

Thanks,
Mike