97 seadoo gtx low compression

[claysimo]

So I bought another old ski 2 weeks ago and have been trying to get it running great. 97 seadoo gtx. It needed a starter wear ring and carbon seal to get rolling OK. Top speed is 48 on my GPS. A bit slow for what it should be with new ring so I checked compression today. Looks like both cylinders are around 120 compression.. also just wanted to mention that it has a rebuilt sbt 787.

Its got ok power out of the hole but feels a little sluggish. Will run 48 for hours though no issues. I'm posting to see if this is typical for these engines with age or if I'm in need of a rebuild soon? This would be my first engine to take apart so I would need some help from the forum if so.. where is a good place to buy rebuild kits and do I most likely just need a top end rebuild or what? Could I do that without pulling the engine out of the ski? Should I try resealing the head and putting a new gasket on there first?
Really not sure where to start any help would be much appreciated

 

[GGuillot]

Looks like both cylinders are around 120 compression.. also just wanted to mention that it has a rebuilt sbt 787.

If that's accurate that's low and time for a rebuild. There's a few places I know of to do a top end bore and piston fit for you. Cautiously I'd recommend Fullbore which I've used, but they've developed a bad reputation for turn around and communicating. There's SBT which is a good turn around, or you can look on ebay there's people on there doing core swaps with you sending your cylinders back to them.

You can pull the cylinders without removing the engine, but I wouldn't. Pros of leaving the engine in, you don't create a mess and a need to realign the engine with the alignment tool when you reinstall. Cons, you run the risk of needle bearings falling in the case and reeking havoc if you don't get them all out. And you won't find any other possible underlining issues, like noisy bearings, etc.

Pros removing the engine, which I recommend and I've done on my 97' GTX and 96' GSX, you break the engine down and ck all the bearings, crankshaft, balance shaft, new seals, and so forth you eliminate potential issues later doing it over. Plus those cylinders laying at a 45 degree can be a fight to get over the piston rings, easier with the engine upright on the workbench. Cons, you'll need the alignment tool later.

 

[mikidymac]

I'd pull it...something not mentioned on here,,,Our shop does not have the alignment tool,,,actually we do,,,we bought an aftermarket one,,,and the holes for the pump would not match up,,,waste of money,,,we have a colleague,,,he has one,,,and so,,,we will try to book him....to come in when he is free,,,
So,,,and I may get chastised on here,,I just index the 2 ,,,13mm securing bolts,,I scribe them,,,and I take closeup pics as well,,,,,,my theory being,,,that if the drive shaft and pto coupler splines have proper normal wear,,,then the motor was aligned properly before me,,,therefore,,,I keep it in the same position,,,,forgive me guys,,,no problems to date.

In theory that works but I have seen quite a few skis that the engine has never been touched have the alignment pretty far off.
I don't know if the hulls sag and flex over time causing the alignment to be off or if they left the factory this way. Another good reason the check alignment.

I know what you mean on the plate not aligning the bolts as my SBT one gets stuck pretty bad sometimes.

 

[etemplet]

I know some people don't check alignment after they pull the jet pump. I do. How this poor bastard ran is beyond me. I really enjoy the adventure in getting these skis to work properly.

I'd use a different and accurate compression testor on the engine. 48mph isn't all that slow. I've tested about 6 GTXs, even the RFIs. None went more than 50mph on the GPS. I"m taking a 97 GTX out this afternoon. Compression is 145psi. We'll see how fast it goes. Providing everything is working properly. Good Luck !

 

[claysimo]

Before i pull it. I'm going to test the compression on my 96 xp which I know had 150 on both heads with a different tester. And test it again on this gtx to be sure.

I changed the carbon ring out and ran it again today and it had more pick up and would go 49mph.. Started and ran smoothly.. I guess once I verify compression tester isn't busted I'll just suck it up and do it the rebuild if it's that low. My xp hauls so much arse I know this gtx doesn't weigh that much more and should be a bit quicker

 

[claysimo]

So I retested compression with another compression tester and it appears the tester i rented from auto zone was bad.. I got a reading of 142 on the mag side and 135 on the pto. This isn't that bad is it? Does it still need a rebuild? Don't want to do it unless I need to

 

[claysimo]

I know some people don't check alignment after they pull the jet pump. I do. How this poor bastard ran is beyond me. I really enjoy the adventure in getting these skis to work properly.

I'd use a different and accurate compression testor on the engine. 48mph isn't all that slow. I've tested about 6 GTXs, even the RFIs. None went more than 50mph on the GPS. I"m taking a 97 GTX out this afternoon. Compression is 145psi. We'll see how fast it goes. Providing everything is working properly. Good Luck !

View attachment 50858

That's tough luck there! I had my impeller shaft break off in the impeller about a month back. I feel that pain.

 

[jhjesse]

So I retested compression with another compression tester and it appears the tester i rented from auto zone was bad.. I got a reading of 142 on the mag side and 135 on the pto. This isn't that bad is it? Does it still need a rebuild? Don't want to do it unless I need to

Those numbers are pretty good for a SBT motor. I have had a couple over the years and that is about as good as you will get.