SX/SXi/SXi Pro All things that could lead to bad compression??

[xDOMBIZZLEx]

So my friend just bought a 98 sxi pro and it ran when we went to look at it. Once we got it home and got it in the water after riding for only 2-4 minutes it died out and wouldnt start so we tow it in and did a compression test. 135-140 in front cylinder and 55 in the back one. Could this be a piston and ring or is this worse than i thought. The guy who bought is already pissed and majorly discouraged with his first ski. need to get this going. any input helps.

thanks guys,
Dom

 

[Mark44]

Yes and yes tear it down and take a look.

Mark44

 

[Fleabags]

Did you check compression before you bought it? May have had weak compression in that cylinder already.
Pull the head and you'll know very quickly if this is a cheap or expensive fix. Whatever you do, make sure you determine why it happened before you repair it. I have seen too many guys invest money in repairs only to have another melt down.

 

[Matt_E]

If it's down to 55psi, that side probably seized.
He may have got lucky and just stuck a ring, but I doubt it.
Pull the head and check the bore.

 

[xDOMBIZZLEx]

gonna get into it tonight. im praying that it just needs a piston and ring. the kid who had it before knew hardly anything about skis. any imperfections i should be looking for on the cyl. walls ring or piston that could help me decipher the problem.

Thanks

 

[Matt_E]

It will be pretty obvious if the bore is scored or not.

Btw, it will need two pistons & rings - not just one.

 

[xDOMBIZZLEx]

it will need one on the side that is at 135-140 psi too??

 

[Matt_E]

You should not be running different size pistons in each side. If one side needs to be bored, both sides are done.

 

[xDOMBIZZLEx]

ohh you meant if the cylendar wall was scored then it needs two. i thought you meant if its just a piston and/or ring it needed two new ones.

 

[Matt_E]

Chances are, it needs to be bored.
Pull the head to find out.

 

[xDOMBIZZLEx]

what could cause that if it started when we went to look at it and when we got it home

 

[Matt_E]

Hard to say.
The gas could have been old and too low in octane anymore. Was the ski running at full throttle when it stopped?
Detonation from the old gas may have done it in that case.
The carburetor(s) may have been dirty and caused a lean seizure.
If the water was cold and your friend just opened it up without warming up the motor first, it may have experienced a cold seizure.
Did your buddy perhaps forget to premix the gas with oil?

 

[sxi steve]

Stock ski compression is 150-150.

FYI- I have sitting on my shelf, perfectly good, used piston assemblies I removed from my sxi-pro and replaced them with wiseco. If ya need to purchase let me know.

 

[Matt_E]

He may need to bore up and use oversized pistons. Are your used pistons stock size?

 

[sxi steve]

Yes.

 

[xDOMBIZZLEx]

It was cold out and it idled for just a few minutes but yea the gas we took out of it looked nasty. definitely had oil in it but like i said the kid who had it before was a sandwich short of picnic. Steve i will let you know if he needs to buy those. My buddy andrew with the Rickter said he has rode with you a time or two, you should come out on lake orion sometime.. but i appreciate the input and will post as soon as i take the heads off and take a look.

 

[xDOMBIZZLEx]

oh and yes the ski died when he opened it up but was just getting to breaking plane he wasnt like wide open across the lake or anything

 

[xDOMBIZZLEx]

just pulled the heads and that cylinder is definitely scored not terrible but i know a little score can go a long way. the issue is he doesnt have the money to be dumping into this. im thinking the cheapest route would be to find a set of used cylinders on here and maybe get those stock pistons of steve..

 

[Matt_E]

Looks like detonation or a lean seizure. Figure $200 for pistons and $100 for machine work, plus gaskets.
The carbs must be gone through and cleaned/rebuilt.

 

[xDOMBIZZLEx]

would it be cheaper to have the machine work done and get oversized pistons or just find used cylinders and get those pistons off sxi steve. if it were my machine id go bigger but he doesnt have the money to do all that.