Compression Question

[blueprint83]

I have a 1996 Seadoo GTX with the 787 motor. The top end was redone about 3 or 4 years ago and I just recently did a compression test on the ski and it was 124 psi in the front and 150 in the back. The ski runs great. but is that 26 psi difference anything to worry about. and do the rave valves effect compression tests as well as the charge of the battery.
Thank You,
-Chad

 

[seadoosnipe]

yes...

Yes to all. Compression results should be performed equally on each cylinder.

Open the throttle fully, then spin the motor over 4 or 5 times. Do this about 3 times to ensure your getting a good representation of your cylinders compression.

The difference your getting is not good. But you may have extenuating circumstances. Charge the battery and check that rave valve.:cheers:

 

[Nate Surveyor]

Something to check

IF one cylinder has a bit of extra oil in it, but not the other, it could give you this difference. I have been reading a bunch here, and somebody mentioned leaking injector oil into the motor, while it is not running. If yours had a teaspoon of extra oil in one jug, but not the other....

I'd suggest running it for a little while, shutting it down, and immediately testing, after pulling it out of the water.

N

 

[blueprint83]

I will run the ski and re perform the compression test. The first test was performed on a cold engine that was sitting for about 5 weeks. and the battery was not 100% charged. Thanks for the help.
-Chad

 

[blueprint83]

Re test

I retested the ski with a charged battery and checked the rave valves over. ( I did not remove but last year they were cleaned)

I did 4 tests on each and made an average. this is what I got 136psi in the front cylinder and 157 psi in the rear. a 21 psi difference. what do you guys think. Like I said the ski functions great. and runs strong. I am just throwing this idea out there, but it had a top end rebuild about 4 years ago, that I did not do. Could the difference be because somebody used two different manufactures of pistons in the motor? I haven't noticed a change in performance since it was done. its just weird to have such a large gap in psi.
Thanks,
-Chad