Low compression 1 cylinder

[Kathy]

I have one motor(starboard) with a single cylinder that has half compression of all others. 120 on all other cyclinders 60 on just the one. Any thoughts for what I need to chase down? I was planning on stage one from group k over the winter but should I with the "bad" cylinder.
Boat overall performs pretty well aside from being a gas hog.
Any guidance is appreciated. Thank you

 

[Bruce]

@speedlng, I believe you have rebuilt one of these. Can you help?

Have you verified that there is oil flow to that engine? It sounds like it is on the way out and lack of oil flow is a common cause.

 

[Kathy]

@speedlng, I believe you have rebuilt one of these. Can you help?

Have you verified that there is oil flow to that engine? It sounds like it is on the way out and lack of oil flow is a common cause.

@speedlng, I believe you have rebuilt one of these. Can you help?

Have you verified that there is oil flow to that engine? It sounds like it is on the way out and lack of oil flow is a common cause.

checked on oil everything seems to be okay there.. Maybe bad wires. Seemed a bit wet on the plugs...

 

[itsdgm]

Sorry to hear about your issues @Kathy. Low compression on a cylinder is an indication of a bigger issue. It's possible that you caught it in time and just need to have some top end motor work done. It's impossible to say without being there. However, I'm sure other guys with more two stroke experience will chime in shortly.

Btw, what prompted you to run a compression test if the boat was running strong? Just curious. Also, do you have pics of what the plugs looked like?

 

[Kathy]

The motor runs a bit rough compared to port side. Also, just wanted to make sure everything was sound only because it doesn't seem previous owner(s) put a lot of time into taking care of the boat the way it should.
No pics of the wet plugs will load up more pics tomorrow. Also the weep holes one the side of the boat seem smokey one more than the other.

 

[Mainah]

@Kathy I agree with @itsdgm compression being 10 psi low is a sign of upcoming internal component engine failure. Super low like you have stated is a sign that motor could fail on you at anytime which obviously is not good when out on the water. Hopefully a top
end rebuild is all that is needed. Also 120 is on the lower side of what is expected for those engines as well.

My last two boats were two stroke jet boats and I rebuilt engines on both of them. I am never going back to two stroke.

 

[JC6275]

@Kathy , It seems you have a engine on the way out, You possibly can get by with a top end rebuild. The weep holes should be "weeping" water not smoke, If you dont have water coming out of the holes when running at more than idle speed you may have a clog. Best thing to do is run weed eater line through both to clean them out.

 

[Kathy]

@Kathy , It seems you have a engine on the way out, You possibly can get by with a top end rebuild. The weep holes should be "weeping" water not smoke, If you dont have water coming out of the holes when running at more than idle speed you may have a clog. Best thing to do is run weed eater line through both to clean them out.

Smoke+water

 

[Kathy]

@Kathy I agree with @itsdgm compression being 10 psi low is a sign of upcoming internal component engine failure. Super low like you have stated is a sign that motor could fail on you at anytime which obviously is not good when out on the water. Hopefully a top
end rebuild is all that is needed. Also 120 is on the lower side of what is expected for those engines as well.

My last two boats were two stroke jet boats and I rebuilt engines on both of them. I am never going back to two stroke.

What's the compression supposed to be? I thought 120 seemed pretty good.

 

[Kathy]

Majorly bummed right now - Just got this thing out to finally enjoy it and the thought of having to pull it back out to spend that much money it and not enjoy the rest of summer.. Major let down.. I was hoping to hold off on any major work until the winter.

 

[JC6275]

120 is not bad, the one with 60 is a problem. Tells me the rings are going quick. Best case senerio pull the head re ring that motor. Put it back together run all season, rebuild both this winter. If you continue to run as is a catastrophic failure will be coming sometime. Could be tomorrow or could make it till winter.

 

[Bruce]

Majorly bummed right now - Just got this thing out to finally enjoy it and the thought of having to pull it back out to spend that much money it and not enjoy the rest of summer.. Major let down.. I was hoping to hold off on any major work until the winter.

It is good that you caught this now. Hopefully it is an easy fix compared to rebuilding the engine.

Do you have the factory oil injection system in place? If so I think that is a good thing but you need to make sure all the hoses are in good condition and that oil is being delivered to all of the carbs. If the rings on that piston failed due to lack of oil then the new set will as well.

 

[Mainah]

I stand corrected 120psi is good for a ls2000. I have only worked on the 717 and 787 seadoo engines and they both had higher compression but seadoo is notorious for maxing out power from a given displacement. I can say across the board that a 10 psi difference is not good and a 60 psi difference is going to have a failure in no time.

Yes it sucks to have this happen during the best part of the season but doing nothing or doing a temporary fix and having it fail on the water can make for a less than good day. Perhaps just one piston or rings is all that needs done. @Bruce has a good point with the oil injection as well.

Regardless the next step is pulling off the jugs to see what is amiss and figuring out what caused it. From there you can address it. The good news is that there are plenty of places that sell parts for these relatively cheap and lots of people who know how to rebuild them if that isn't something that is up your alley.

Good luck.

 

[Kathy]

It is good that you caught this now. Hopefully it is an easy fix compared to rebuilding the engine.

Do you have the factory oil injection system in place? If so I think that is a good thing but you need to make sure all the hoses are in good condition and that oil is being delivered to all of the carbs. If the rings on that piston failed due to lack of oil then the new set will as well.

I believe Oil is getting into everything as it should but I will double check.. Sadly the plan is to start pulling the top end off and see what the heck is going on, but I'd rather do that then have to replace the motor. - major bummer

 

[itsdgm]

Good luck @Kathy and keep us posted. We're all pulling for you. Hopefully it's a quick and cheap turn around.

 

[Kathy]

Looking like a rebuild I think.. Wiggle in #2 and scoring. Now it's a matter of whether to pull the whole thing or do a partial rebuild. Who would be the best to do this work if I were to send it out? Closer is better..
I called GroupK - guy was pretty great to talk with and make recommendations for what may have caused the failure. He's suggesting sending the head, cylinder, carb bank and manifold if I send parts to them.. otherwise could try the honing to get those grooves out - but still more forensics on the culprit that caused the problem to start with should be done. who knows what the lower end condition is at this point.. UGH... Guess she's down for the count this summer.. boooooo!
Here's some pics -

 

[Bruce]

Some like them, some hate them but SBT will swap the engine for a rebuilt one for $945 plus shipping http://www.shopsbt.com/jetski/yamaha-engine-1200-non-pv-gp-xl-suv-exciter-97-05.html

But if oil supply or something else external to the engine was the problem it will reoccur.

 

[itsdgm]

IMHO rebuild the carbs and inspect/replace the oil lines with whatever route you go on repairing/replacing that engine.

A dirty carb can cause a lean condition and a bad oil line can reduce lubrication. Either one could've caused this issue and will cause the new repair to do he same if not fixed first.

Hopefully you can get this fixed ASAP so that you can get back out there on the water soon.

 

[4x15mph]

Sorry about the bad news but fortunately on a 2 stroke this is relatively inexpensive. Hard to diagnose from here but you do need to fix the culprit. I think many of the bad stories about SBT is because of people just swapping an engine without fixing the problem and the fact that SBT is a common route for these situations. That said, I would go with their premium option. If you don't care about down time, I would consider some other rebuild options including DIY.

I would recommend pulling apart your cooling (exhaust chamber) as well as the carbs and oil line inspection.

 

[Kathy]

Sorry about the bad news but fortunately on a 2 stroke this is relatively inexpensive. Hard to diagnose from here but you do need to fix the culprit. I think many of the bad stories about SBT is because of people just swapping an engine without fixing the problem and the fact that SBT is a common route for these situations. That said, I would go with their premium option. If you don't care about down time, I would consider some other rebuild options including DIY.

I would recommend pulling apart your cooling (exhaust chamber) as well as the carbs and oil line inspection.

I'd like to go the least expensive route even if that means pulling the motor and doing some dirty work - I'm having a hard time finding good pricing for justifying the DYI vs Pull and core the motor for a rebuild. I'm looking for possible donor motors as well - not sure if an XLT1200 or the GP1200 or ?? will work best. I found a ski that might be a good candidate, but unsure if it will work as a "temp" solution so I can yank swap and rebuild the stock motor. If you all can't tell I'm really wanting to stay on the water... GroupK says they're pretty slammed right now so I wouldn't get any sort of a quick turnaround.
I'm already over $$ value on the boat now - not that it has stopped me before for moding over the value - but who doesn't like to go faster really...