Compression Variance - 99 SPX

[KCseadoo]

Project Ski - compression variance
Recently bought a project ski - 1999 SPX with the 787 motor. Quit running on the seller and wouldn't start anymore.

Rear - 150 psi visual inspection is fine
Front - 115 psi vertical scoring on the cylinder walls. About 6 vertical lines (should have taken photos)

Operational Question
What happens if the ski is ran with such a large variance?
What additional stresses are placed on the components?

Rebuild Question
1. Sleeve or oversize the cylinder?
2. Sleeve the bad one and leave the good one alone?
3. What causes should I be looking for regarding the source of the scoring? (fuel / oil / seizing)

Overview
Doesn't appear that the seadoo received any maintenance.
1. Jet Pump oil was a black sludge
2. Rave valves were a gooey mess
3. Changing out the fuel lines (however, the lines don't show any deterioration)

The ski starts and runs, but haven't dealt with the compression issue or the cause of the cylinder scoring.

Ultimately i will fix the problem, The question is whether i need to address it immediately this coming week or if i can take it our for a ride. It's still in the garage being gone through right now.

Thanks

 

[jords]

running an engine with that much of a diffrence can cause the engine to run unevenly, it can cause it to overheat also. So do you risk doing more damage for a weekend of fun?


I would replace just the one piston if the other one looks good, and if the walls are scrotched then I would resleeve and match it to your other piston, so when it comes to the next top end kit, you just get matching pistons or a top end kit


and scoring usually means foreign material or a ring falling apart

 

[chuckydoo]

I would without question do a total top end. The base gasket is under both cylinders and when you remove one you need to replace. Also if there is alot of hours on the other cylinder it can go down hill fast. Why waste your time, do both and know what you have.

 

[KCseadoo]

Suggestions on where to have the cylinder honed/bored? I assume there are people specializing in the seadoo heads?

 

[timmyboy76]

any machine shop, will do it.