Engine Failure of some sort Rotax 717

[ddanster]

Wanted an opinion of the possible failures that occured before tearing it apart. I took both of my seadoo gs out last weekend. My buddy was riding one and ran perfectly for about an hour. Suddenly the engine cut out on the 1999 seadoo gs and would not start. Plenty of fuel, is oil injected with a little premix. It did sound abnormal when attemping to start it again on the water. I pulled it out of the water and it would crank normally but would not fire what so ever.

About a month ago I did a compression test and it was sitting about 131 PSI on each cyclinder...worn but runnable. I tested after this failure and it was about 120 PSI in each cylinder...rather abrupt drop. Spark is strong and fuel supply is not an issue. I removed the air silencer and sprayed a little starter fluid into the carb..it spits but never fires up. Spark plugs were a bit dry so it was running a bit lean I believe. Perhaps timing went kaboom i dunno.

Think I provide enough info..what do ya think?

 

[CReynoldsMIZ]

Seadoos have a hard time running at all at 120 psi. I would look at rebuilding your top end or getting a new motor if those numbers are right. I'm in KC as well.

 

[LouDoo]

I agree, your engine is tired.

Lou

 

[- BiRkS_]

I agree, your engine is tired.

Lou

Not trying to step on anyone's toes...but if the engine SUDDENLY died, and still has fuel, spark and acceptable compression, I would be looking at timing (rotary valve, flywheel key).

Yes the compression is low, but should have no problem firing up on the trailer. Don't use ether or starting fluid. its highly explosive and has no lubrication. Pour a teaspoon of premix fuel down each spark plug hole and see if it fires (2-3 seconds run time) Then try it through the carbs. If it backfires or spits fuel out of carbs, I would take RV cover off and inspect the rotary valve and its timing. (perhaps a stripped gear, or a bolt fell in there and made a mess inside)

An engine needs 4 major things. Fuel, spark, compression and timing. Start eliminating the easy ones like fuel and spark. Re-check compression. Cold engine, WOT, 3 tests, take the middle reading. Post back with your findings.

 

[ddanster]

Thanks for the info everyone

 

[ddanster]

I managed to find some time to take apart the engine further. I took it apart to where the Rotary valve is exposed. I removed the spark plugs and spun the pto by hand. I noticed while I turned it it seem to get held up and the Rotary valve would stop moving as I continued to turn the PTO then resume turning with the PTO. Looks like that whole connection to the rotary valve is jacked up.

 

[jammin777]

sounds like a sheared rotary shaft gear?

 

[LouDoo]

Yes, I agree, but with 120psi compression, IMO, you would be wasting time and money, time for a rebuild, or a rebuilt engine.

Lou

 

[ddanster]

Yeap new engine time!