Superjet low compression

[DezKnotz]

So I was out on the ski and it ran great just the other day with no sings of a problem. Today I was checking the psi on another ski so I checked the sj and I had 185 in the front and 110 in the back cylinder. I have a b pipe and a ada head and it's on the original top end on an 09 so I guess it's time. Is it possible I just need rings or do I need a complete top end

 

[SmittySX]

Pop the head off and inspect.

 

[Moto360]

Just my 2cents. Something is wrong. Something happened to make that cylinder loose compression. Head o-ring, cracked dome, worn piston and rings, worn rings, stuck rings from a melted piston, or crank is on its way out and bearing pieces are bouncing around in motor hurting piston and rings

 

[Wizards Powersports]

We have Pro-X 82mm piston kits here (1mm over stock). $99 shipped for two kits (enough to do your top end).

 

[DezKnotz]

Time for a new top end the rear cylinder has a chip missing

 

[KawiKid]

@DezKnotz when you say a chip, do you mean like a chunk missing out of the top of the piston?

 

[DezKnotz]

Yes it was a chunk from the top part just above the ring @KawiKid

 

[erik mx45]

need to find the chunk flush out bottom end of motor for any debris

 

[Tyler Zane]

You really need to take that whole motor down. Inspect the crank, check rod end play, replace crank seals, bore hone cylinder, new piston and ring set... Double, triple check ring gap...

do it all right the first time and you will have a motor for years to come. don't disassemble it and you may have the crank let go next season.

 

[DezKnotz]

 

[DezKnotz]

Is it weird to have what seems to be a surface rust on the crank like that ?

 

[DezKnotz]

That's the chip in the piston

 

[Tyler Zane]

That bit of surface rust could of been from a long time ago. It happens... clean it up and start fogging your engine. Other than that the rod thrust washers look tight but looks only get you so far.

That is one burnt piston! That's not a chip. That happens over time from heat, lean mixture etc. You have no piston wash at all. Leaky crank seals could be a culprit along with dozens of other factors.

Time for a rebuild and tune. I still advise going threw the entire engine like I stated in my first post.

 

[Tyler Zane]

And I'd port the cylinder at the very least. It's not about playing it safe or not, a ported engine can be just as reliable.

 

[cookn]

Yea you are lean for sure causing the edge of the piston to melt, and rust on a crank is never a good sign in my opinion. Usually means water or moisture has sat in there at some point

 

[cookn]

 

[DezKnotz]

What's piston wash ?

 

[Tyler Zane]

Google it

 

[DezKnotz]

If I would be at wot for a good couple seconds the ski would shut off like it's out of gas, then it's would be hard to start and then ran fine again. Would this happen from being lean or is this a jetting issue. If so how do I fix

 

[Kyle Chandler]

Have you checked your carbs internal filter for debris? Also check your fuel sector, make sure its not restricting the flow. Cause you were definitely lean looking at that piston.