GTX LTD bad compression

[andy.262]

I have a 99 GTX LTD that was running OK until it all of a sudden stalled. Now it will barely start, and will only run for like half a second before stalling again, and it sounds like there's some kind of rattling happening. Compression is 120 in front and 150 in back, so obviously that's a problem. I just can't really figure out why. RAVE valves are not damaged at all. I took off the head expecting to find damage to the cylinder or piston, but to my novice eye nothing seems wrong. Then again, I don't really know what I'm looking for so what do you guys think?

Pics in order: head, back cylinder, front cylinder

 

[etemplet]

DISREGARD MESSAGE I thought this was a DI engine. Oops !!

I'd check the fuel pressure and air pressure. First I'd check the small hoses coming from the air compressor that go to the rave solenoid and make sure all that is ok. Make sure the rave solenoid is holding and working.

Sounds to me more like a fuel issue than compression. Cylinders look pretty good. I'd check compression again but you already have the head off. Good Luck !!

 

[andy.262]

I checked compression a few time, since I didn't want to believe what it was telling me lol. Even verified my compression gauge reads correctly on my other ski which I know has good compression.

Would a bad RAVE solenoid cause bad compression? I replaced it a while ago, but I couldn't find the SeaDoo part so I replaced it with the equivalent Ski-Doo part (which was also used)

 

[etemplet]

No reason for the raves to be damaged. Your pistons are 1mm over which is about the last size I use. You can go bigger of course it just costs more. Measure the cylinder bores since you have access. I don't see a reason why compression would be low other than normal wear. As for the 150psi reading that seems very strange.

 

[andy.262]

150psi is the target for a "healthy" engine, no?

 

[etemplet]

I checked compression a few time, since I didn't want to believe what it was telling me lol. Even verified my compression gauge reads correctly on my other ski which I know has good compression.

Would a bad RAVE solenoid cause bad compression? I replaced it a while ago, but I couldn't find the SeaDoo part so I replaced it with the equivalent Ski-Doo part (which was also used)

I was thinking you have a DI but it doesn't look like one so you have a carb ski correct?? I have DI on the brain right now cuz I'm restoring one and helping a guy troubleshoot his DI.

 

[andy.262]

correct, its a 951 carb ski (99 GTX LTD)

 

[etemplet]

150psi is the target for a "healthy" engine, no?

Oddly enough I've never checked compression on a new 951 engine, even the ones I have built because I have no reason to. LOL Lots of people here say 135psi is new compression on a 951. Maybe I'll check the one I just installed. Ha ha.

 

[andy.262]

it seems weird to me that it would be a fuel issue - I just had the carbs rebuilt by a mechanic I trust (he used the correct genuine Mikuni parts, even refused to do the job without them) and the engine itself is brand new from SBT last season. Plus the issue started very suddenly, it was on the water and running fine until it suddenly stalled, when I turned it back on there was/is a loud rattling noise that wasn't there before and the engine dies after half a second of idling. It will start but barely. If it was a fuel issue it wouldn't have happened so suddenly, right?

 

[etemplet]

OK Brain reset engaged. Did you check for something in the impeller just to rule out weird stuff.
On the engine, check for looseness on the piston on the low pressure cylinder. Turn the engine over by hand and make sure the pistons come all the way to the top. Then see if the low pressure cylinder piston moves down right away when you turn the engine very slowly. Push on that piston and hope it doesn't move down when you do. Could be a wrist pin on connecting rod bearing causing the low compression and the engine noise.

 

[etemplet]

Good thing is you have a SBT engine and it is likely under warranty. I''d contact them and ask what to do. I think you are correct in saying it isn't the carbs. Engine noise is never good. I'm not gonna rag on SBT cuz a lot of people do. I just pulled a 5 hour run time SBT engine from a 951 that had a broken piston. So be safe and contact them. Low compression is their problem.

 

[andy.262]

Yeah unfortunately this engine is the result of warranty-ing the previous SBT engine that failed, and the warranty is now expired. I will never go SBT again, I'm doing my own rebuilds from now on, the 787 I rebuild 4 years ago is still going strong.

I put this ski up for sale as soon as it broke, I'm just so sick of working on it and I don't even really like that hull style that much, I really prefer the smaller X4 hulls. I'm mostly just trying to diagnose the issue so I can put it in the listing and hopefully get more bites if people know what they will have to fix.

Impeller is clear. I will try checking for piston looseness after work today and report back

 

[etemplet]

Bummer. It does help if the ski was well cared for and looks nice. Your electrics are working so that is a BIG plus, carbs redone which is very good as well. Top money to be would be $1000 in my estimation. Good Luck !!

 

[etemplet]

Yeah unfortunately this engine is the result of warranty-ing the previous SBT engine that failed, and the warranty is now expired. I will never go SBT again, I'm doing my own rebuilds from now on, the 787 I rebuild 4 years ago is still going strong.

I put this ski up for sale as soon as it broke, I'm just so sick of working on it and I don't even really like that hull style that much, I really prefer the smaller X4 hulls. I'm mostly just trying to diagnose the issue so I can put it in the listing and hopefully get more bites if people know what they will have to fix.

Impeller is clear. I will try checking for piston looseness after work today and report back

That is my favorite 3-seater hull style. LOL I like the smaller skis too but I restored a 2000 RX and.... I like THAT one for sure. It's got some grunt!. I only did a top end on the 951 in installed in the RX. It has about 6 hours on it as I don't ride much. The engine came out of a 1999 GTX that felt pretty good when I checked everything so I just did the top end. It's my ski so if it blows up no big deal. LOL I would have had to spend the money anyway.

 

[mikidymac]

Something is off.
Perfect compression for a carbed 951 is 130psi.
No matter but a difference of 30 psi is a big problem.
Those pistons look lean and it is hard to tell but the cylinder walls don't look great.

SBT

 

[andy.262]

Turns out one of the small oil lines that runs from the oil pump to the intake detached itself at the oil pump. Very frustrating that something so simple destroyed my brand new $1500 engine - and I guess it wasn't SBT's fault after all

 

[etemplet]

I'm not familiar with SBT but I've read they have "no fault" warranties. If you had more material in the cylinder bore you could just do a new top end. You can get the larger pistons though but it will be more expensive. I'd clean the bottom end and do a new top end.... easy peasy.

On the oil lines.... they are the life of the engine for sure. Not all are equal even when they say Tygon. I had new an oil line disentegrate on a DI. Thankfully it was the line to the compressor and I was able to rebuild that in place. Now I test ALL the oil lines, place them in laquer thinner for 15 minutes and I burn the material as well. I'm gonna find a good source and stick with them.

 

[mikidymac]

I'm not familiar with SBT but I've read they have "no fault" warranties. If you had more material in the cylinder bore you could just do a new top end. You can get the larger pistons though but it will be more expensive. I'd clean the bottom end and do a new top end.... easy peasy.

On the oil lines.... they are the life of the engine for sure. Not all are equal even when they say Tygon. I had new an oil line disentegrate on a DI. Thankfully it was the line to the compressor and I was able to rebuild that in place. Now I test ALL the oil lines, place them in laquer thinner for 15 minutes and I burn the material as well. I'm gonna find a good source and stick with them.

It is pretty inexpensive directly from Seadoo and should last another 20 years.

 

[etemplet]

It is pretty inexpensive directly from Seadoo and should last another 20 years.

What about that stuff OSD sells? I never order from Seadoo because of their shipping charges and when you look at the oil line it doesn't tell you the length so it is only for one ski I assume. I don't have a problem ordering from Seadoo though if I could just see what I'm getting. I'd like to have 10' of each size in my stock pile, especially the 8mm and 12mm.

 

[mikidymac]

Never tired the OSD stuff.
At one time Seadoo sold it by the foot so I orderd like 5' but they sent me 5 packages so about 20' and I have barely made a dent in it.

 

[burtshaver2021]

What about that stuff OSD sells? I never order from Seadoo because of their shipping charges and when you look at the oil line it doesn't tell you the length so it is only for one ski I assume. I don't have a problem ordering from Seadoo though if I could just see what I'm getting. I'd like to have 10' of each size in my stock pile, especially the 8mm and 12mm.

I ordered this small oil line from our local BRP dealership for one of my snowmobiles, it’s the same line for the seadoo’s Part number 219704404. It was 1500 mm long which is 5 feet and I paid 20.99 Canadian plus tax for it which would be about 0.50 in US funds. I’ve never ordered the 8mm and 12mm, for whatever reason those sizes always seem fine but I think I will order some anyways just to have. The oil lines are one thing I like to buy OEM.

 

[WhiskeyD]

OSD hose is good stuff. I've used all sizes they sell with good results. Also have used ebay/amazon fake tygon and they cracked within a season or two so definitely make sure its genuine Tygon if going through ebay/amazon.