Low compression rear

[tj21]

2 summers ago the seadoo was running fine for a couple trips, then died after I put new gas in it. I assumed carbs were plugged, but put it away.

I finally got around to cleaning the carbs. I took them completely apart, soaked them in carb cleaner for a night each, washed with water and dried with compressed air. Everything looked good and I think I did a good job.

Then I put some Marvel Mystery Oil in the spark plug holes, as someone suggested on here for neglected engines. After soaking 48 hours, I did a compression check. Both cylinders were 155.

Took the seadoo out, and it would only get up to 30 mph, when it used to go 55+.

I then checked my carb screws, checked the carb filters, and replaced the fuel lines with Napa lines.

Took it out again, and it barely started. I could get maybe 15mph and it would die.

Tested compression again. Front cylinder was 150. Rear was only 45.

Put couple teaspoons of 5w20 in the rear. Test brought compression to 75.

Now what? Do I need to rebuild for certain? What causes this? Bad oil pump?

 

[flip6]

You are probably getting high compression reading because the the oil you are adding is helping the pistons seal.

Remove the head and the barrels and make sure the rear piston and rings are good. Possibly broke a ring on the rear cylinder which was the cause of your original problem.

 

[Dr Honda]

The oil is sealing the rings, and is a false reading. you check compression with a cold engine, throttle open, and dry cyl's.


It's time of a rebuild.

 

[tj21]

Here's pictures of the damage. Can anyone tell me the amount of work involved and expense? I have replaced a car engine by myself, but never rebuilt one, and have little experience with seadoos. I don't even know if its just replacing the pistons, boring out cylinders, or ???

I'm debating whether to fix or sell as-is.

 

[Dr Honda]

That sux.


Pull the jugs off, and have them cut to the next size, and get a top end kit, and put it back together.


It's not hard to do... and you can probably do it for well under $500.

 

[greyrider]

Hey Doc, do those ports look sharp to you or is it just the pic. Arent they supposed to be eased more? or not?
thanks
And good luck with the re-build TJ.
I will be digging into mine soon, busy with getting both xp's dressed up before 951 job. only 25psi in rear cyl.

bobby

 

[seadooya]

the walls of the cylinder, dont look bad. Probably get away with just a hone on that side, and new piston, and be done with it.

 

[Dr Honda]

Hey Doc, do those ports look sharp to you or is it just the pic. Arent they supposed to be eased more? or not?
thanks


bobby

Yes... from the pics, they look sharp, but the chamfer can be small.

 

[flip6]

You've also got to find out what caused this to happen so after the rebuild it don;'t happen again.

while i were there i'd put new kits i the carbs and i'd check two stroke oil delivery from the oil pump.

Might have just been a dodgey piston but best do all you can to ensure you don't get a repeat.

Just rebuilt mine - very easy