One cylinder with 0 compression

[Xavrie]

I did a compression test and got 150 on one cylinder and 0 on the other. What should my next step be?

 

[Coastiejoe]

Pull the head,,

 

[Bills86e]

Pull the RV cover & Head.
Could be shot Piston or RV gear/plate.

 

[Xavrie]

Ok... Pulled it... Looks like I have a damaged piston.

 

[Xavrie]

 

[Coastiejoe]

Yep. Depending on how many hours are on the crank, time for a top end.

 

[Xavrie]

Would the piston still move even if it's bad? Does this look like a bad poison?

 

[Coastiejoe]

Yes, it is attached to the crank. So if the crank is moving the piston will move One exception, connecting rod or piston broke. That's the only way it wouldn't move.

 

[Xavrie]

Ok so your opinion would be new top end?

 

[Coastiejoe]

How many hours are on the crank? If it is 300 ish, then a full rebuild or re-engine. If 150 ish, then a top end would likely be fine.

I would try to determine WHY you had the failure. If you don't solve that, you'll be fixing your new repair.

 

[Xavrie]

So.. This started because the jet ski was bogging down in water and would not go higher than 3k RPM. I replaced all below:
Gray fuel lines
Fuel filter
Fuel selector
Cleaned out carbs
Still bogging down. I checked the RAVE Valves I noticed the one valve that was stuck which now explains why piston was shot.I pulled it out and and replaced the entire RAVE Valve. Still didn't work. I decided to did the compression test and here is where we are now.

I'm really not sure how many hours this has but this is a 20 year old jet ski.

 

[laug6615]

Hey, I'm really interested in seeing what everyone's opinion is on this guys situation. I have a 94 GTS that I just discovered that has low compression and trying to determine whats cost effective, top end rebuild, full rebuild, engine replacement or just cut my losses. So everyone that can please post up what you think.

 

[Coastiejoe]

Anything 20 years old and unknown hours, you at the minimum have to pull the crank and check clearances and bearing. If it is nearing 300, total rebuild and replacement.

 

[mikidymac]

IF you are going to keep the ski for at least few years I woud to the to and bottom end. IF you are unsure and only think you will keep it and everything else looks good then just the top end.

 

[rshaw]

I had the same thing happen too me, wouldn't go above 3000rpm and ended up blowing the piston only too fix it and have it happen again to the same cylinder. I did everything you did the first time it happened too. This time I figured it was an oil issue so I blocked off the oil injection and I'm going pre-mix. It's something to consider if your doing work on it.

 

[mikidymac]

99.9% of the time it is not the oil injection. If you only lost one cylinder and the little oil line didn't break then it probably wasn't the oil system. 9 times out of 10 on these ski's it is a fuel issue causing one cylinder to run lean.

 

[SabrToothSqrl]

20 year old bearings, crank, etc?

I'd send the engine to a rebuild shop, get a no-fault warranty, and run it another 20 years.

 

[rshaw]

99.9% of the time it is not the oil injection. If you only lost one cylinder and the little oil line didn't break then it probably wasn't the oil system. 9 times out of 10 on these ski's it is a fuel issue causing one cylinder to run lean.

I see; sorry then! I read in a few places it could be oil so it wasn't a big deal for me to just block it off and eliminate that that could be it. Would you suggest a carb adjustment then or should I be looking elsewhere in the system?