98 GTS - Lost compression on one cylinder today - verify top end rebuild???

[vallentinerocks]

Took the Skis out for the first test run today. My XP wouldnt start and never got off the trailer.. The GTS started up fine and ran great for about an 45 mins.

Ran good and strong until last run, and while riding the ski shut off on me, thank god i was only 60 feet from boat ramp when it died. At first engine would not turn over on first few attempts, like it was locked up. after a few more pushes of the start button, it turned over but would not fire up again. I limped back to the boat ramp.

Got it back on the trailer and out of water and immediately checked compression. One cylinder was normal compression, the other one would barely give me a reading ( like 5psi). Both plugs were dry when pulled and inspected.

What exactly did I lose in the failed cylinder?? Rings, piston,etc... and what happened?? the piston is still operating, and you can feel air out of the spark plug hole when cranking, but like I said the compression is close to nothing. Besides the obvious, is there anything else that can wipe out compression in one cylinder only??? please advise. thanks.

 

[LouDoo]

Just guessing sounds like the rings, since the motor isn't seized you might get lucky and only have to replace the rings. I would go ahead and pull the head and take a look.

Lou

 

[vallentinerocks]

ok.... when i inspect the cylinder and if its just rings, what exactly will i see to verify its rings, and then can i just change rings without additional parts or machining?? the other cylinder compression is about 122psi so was figuring a top end rebuild for both sides for better compression, so should i do a complete top end rebuild instead even if its just one set of worn rings on the other side??

not sure what kind of compression readings i might get with new set of rings only, and will it mismatch with the 122 on the other cylinder. btw, the ski was running great, seems like it was reaching max speed.... had no starting or idles issues and not really any hesitation. good response. it was a good 45 minutes on the water

 

[Dr Honda]

if you are way down at 5 psi... there's going to be a big hole in the top of the piston. Plan on sending both jugs out to be bored, and 2 new pistons to be installed. (Assuming your crank, and crank seals are good)

 

[vallentinerocks]

opened it up today to see pistons. the top ring is damaged and about an inch and half of the top edge of the piston too. doesnt appear to be any damage to the cylinder wall, atleast nothing the bore wont smooth out. theres still water in around the cylinder walls as i could not blow out the water from yesterdays run, so it shouldve have been cooled fine. no water was present inside the cylinder and spark plugs were fine. hopefully a top end piston rebuild will take care of it. it was running great.

 

[brock1]

If the motor was locket at first you are most likely going to have cylinder damage. When a motor locks like that it is usually the rings got to hot and were stuck to the walls after you get the jugs off you will probubly see scratches on the walls.plan on a rebuild

 

[vallentinerocks]

yep, looks like the top ring is where it started... gonna do a top end rebuild. the section of wall inside has minimal damage and can be resurfaced smooth and even with the bore it appears.