1995 Speedster top end nightmare

[Kyle92]

Hey so new to the seadoo world, worked on a lot of 2strokes but not in a seadoo.

Bought a speedster with one cylinder reading zero compression, opened and rings were melted to the piston. Did a new top end kit and within first hour noticed some minor heat in the same cylinder that was damaged. Removed the head today and found out the cylinder is damaged once again. Im not worried about rebuilding again but obviously I have to figure this out because i thought I'd have some time to figure it out once it was running.

First two pictures are from before rebuild

Second two pictures are from after rebuild

 

[mikidymac]

Dirty fuel system and carbs running lean. Pretty common around here.

 

[Kyle92]

Thanks for reply that's what I'm thinking , should of been smarter than trying to run it again. Learn and live

 

[Dr Honda]

It could have been a bunch of stuff. As above... plugged carb. But it could have been a crank seal leak... timing that was high.... a "Squash Band" that was out of spec... high cyl clearance... or a ring gap that was wrong.

Also... what oil were you running? AND, did you verify that the oil injection was working? (filter plugged, injection nozzle plugged, check valve plugged, or broken hose)

When rebuilding a 2-stroke... there's a bunch of stuff that needs verified.

 

[Kyle92]

Thanks for all the places to start looking, I'm more than likely going to take the engine out and go over all fuel and oil components. I really need to start getting my self familiar with exactly how this boat works.

 

[mikidymac]

It could have been a bunch of stuff. As above... plugged carb. But it could have been a crank seal leak... timing that was high.... a "Squash Band" that was out of spec... high cyl clearance... or a ring gap that was wrong.

Also... what oil were you running? AND, did you verify that the oil injection was working? (filter plugged, injection nozzle plugged, check valve plugged, or broken hose)

When rebuilding a 2-stroke... there's a bunch of stuff that needs verified.

Squash Band?
Like this?

You mean squish clearance Dr.? LOL.

 

[Dr Honda]

Exactly !!!! LOL.

The squash clearance is the distance under the squash band. The squash band is the secondary lip in the combustion chamber. Proper clearance quenches/cools the edge of the piston crown. Too much clearance allows heat/burning fuel on the exposed top ring. Too tight, and you create a secondary compression heat source.

 

[mikidymac]

Exactly !!!! LOL.

The squash clearance is the distance under the squash band. The squash band is the secondary lip in the combustion chamber. Proper clearance quenches/cools the edge of the piston crown. Too much clearance allows heat/burning fuel on the exposed top ring. Too tight, and you create a secondary compression heat source.

I know what it is, I was just giving you a hard time because I have only ever heard it called Squish, even in the manual it's squish. You are the only one I have ever heard it called Squash so I was just giving you the business.

 

[Kyle92]

I never did check the squish or squash which ever were calling it hahaha, the top end when I first opened it did have a piece of the piston cracked right on the crown but luckily found the piece in my exhaust.

 

[Kyle92]

This is the spark plugs one from each engine. Some tell tail signs of running lean but from the sounds of what happens with a bad squiash gap seems like that could cause exsesive heat and make the plugs look this way.

 

[mikidymac]

That top plug doesn't look good.

 

[Kyle92]

The one on the left is from the engine that's running good, the one on the right is the engine that has one cylinder over heating and destroying piston/ cylinder