97 Seadoo XP 787 compression

[danzimal]

I just bought a 1997 XP (and my first Seadoo)
It is really clean and the seller said it had no problems.
Unfortunately, the battery was dead so I took it without seeing it run.
I know; stupid is, stupid does.

Anyways, after I charged the battery and fogged the cylinders and got it to crank, I checked the compression.
The front compression is maybe 10 PSI, the back is 150 PSI (crap).

The piston is moving, and it doesn't look like its a gasket.
Any idea's as to why this would happen?

 

[lexer440]

Re: 97 Seadoo XP 787 compression

Lift the heads off and take a look at pistons, cylinders, heads and gasket condition. if the motor turns over smoothly and crank appears ok you maybe looking at top end rebuild. Post pictures if you can and people here will help you right direction.

 

[dannyual767]

Re: 97 Seadoo XP 787 compression

It's the oldest and most committed mistake in the used PWC buying game. For anyone else reading this......Never, ever, ever buy a used PWC without checking the compression first!

The only way you could buy one without checking the compression is if the price was so low ($200-$300) that you pretty much knew that the engine was junk and a rebuild was in order.

danzimal, I sure hope that you didn't pay all that much for that ski. As has already been mentioned, at the very least, you're looking at a top end job. The cylinder is low on compression probably because it was starved for oil or ran lean due to a carb problem. Both very common. Or it could've been water ingestion due to a bad exhaust gasket.

Take the engine apart and have a look to ascertain the damage. Plan on a full rebuild of both carbs as well. You must find the cause of the problem before you fix the engine. If you don't, you're looking at trashing your next engine the same way this one was trashed!

Check out this link for a smokin' price on a top end kit: http://www.pwctoday.com/showthread.php?t=381999

I'm currently using those same WSM pistons in one of my 1996 SD XPs. They work great.

 

[danzimal]

Re: 97 Seadoo XP 787 compression

yeah, I'm in a pickle.
I think I can manage a top-end and even carb rebuilds, but not much beyond that (as in a complete engine rework).
I might be better off replacing the engine from some someone like fullbore for +/- $999.
you think?
Dagnabit.

 

[dannyual767]

Re: 97 Seadoo XP 787 compression

Before you go making plans, it would be wise to find the extent of the damage to the current engine. In other words, take it apart and see. It was very easy for me to remove the 787 out of my '96XP. I don't know how hard it is to remove from a '97. You may not need to remove the engine from the hull but it sure makes it easier to work on.

As I already posted, you've got to determine what caused the trashing of the front cylinder. Is the ski still oil injected or has it been converted to premix?

Assuming nothing is wrong with the bottom end, you're only looking at a top end job and carb rebuilds. You've said that you think that you can handle that. I had never really done any real jet ski wrenching prior to this year with this '96 XP. It had two freeze crack cylinders. I'm very mechanical and do all of my own wrenching on everything that I own so this was new territory but not difficult at all. Way easier than rebuilding car engines which I'm quite familiar with.

Find out the extent of your damage and determine what caused it before you do anything else.

 

[danzimal]

Re: 97 Seadoo XP 787 compression

I'm not sure when I can get to it, but I will definitely post some pictures seeking guidance.
thanks!!!

 

[shagy959]

Re: 97 Seadoo XP 787 compression

when you do the rebuild even if the bottom end is good replace the outside crank seals ive seen it a ton of time that was a reason that took out the motor also make sure the oil lines are good alot of times one will split or fall off easy sign oil in bottom of hull

 

[danzimal]

Re: 97 Seadoo XP 787 compression

I finally got around to pulling the head off my XP.
I don't know much, but this doesn't look good.
I looks like the front cylinder is scoured and there are a couple of loose chunks of something on the top of the head.



It may look a little junky probably because I fogged the cylinders before I even tried to crank.
What do you think?

 

[lexer440]

Re: 97 Seadoo XP 787 compression

I would rebuild it completely including the crank, the crank may seem fine now but I would not expect it to last long as the bearings and seals have probably been compromised.

You will need to remove it from the hull, put the heads back on to take the flywheel and PTO wheel off. drop a short length of rope in through spark plug hole, (thats why we put heads back on), this will prevent engine from turning while you undo those.

For the PTO wheel you will either have to buy a spline socket or take it to a dealer that will charge a few bucks to remove it.

 

[Old Screwball]

Re: 97 Seadoo XP 787 compression

When I blew up my GTX Limited (the first time) it was because of a clogged filter to the rear cylendar, it ran lean and eventually burned a hole in the piston. I opted for a long block. New motor was $1800. Lasted 2 years before blow up #2. Actuating rod from throttle to oil pump broke, Doo was running full throttle with idle mix oil. Made it all the way to Lake Havasu and 1/2 way back (55 miles) before it let go. Did a quickie rebuild and traded in both GTX Limiteds for a pair of 4 cycle GTI-SE 155hp.

 

[86 century]

Re: 97 Seadoo XP 787 compression

That cylinder has gone lean leading it to melt the piston.
all the dents are from pieces bouncing around between the piston and head.

The 787 eng family has a problem with the center crank shaft seals going out so beware of used long blocks.