SX/SXi/SXi Pro 0 Compression on Cylinder 1

[zpike00eb]

Hello!

Just bought a '93 750SX off a local guy for pretty cheap. It ran 148/148psi day one and ran pretty well, had some starting issues. Took it out for the weekend and it crapped out, wouldn't start. Initially thought it was head gasket related because it was overheating, but as it turns out I had completely lost compression.

Today I replaced all the gaskets on the top end, cleaned out the water jackets the best I could ( trying to hunt down overheating ), and replaced the starter. Did a compression check and found 0-10 (gauge doesn't go that low) PSI in cylinder 1 and 148 in cylinder 2. Engine turns over with no resistance.

So what did I lose, and where do I start? Never really wrenched on standup's before. The cylinder is a grayish color.



Thank you for any tips/advice!

 

[zpike00eb]

So I stripped down the engine... (Took less than 20 minutes with air tools.. These skis are awesome) expecting to find a melted or fractured piston, or missing rings. All I could find was the rings on the affected cylinder were 'pushed in' to the piston itself, while the 148PSI cylinder rings are free floating around the piston. Also found the the 'lower' gasket was like wet cardboard and turned to a slime when taking it off.

The rings came out of the cylinder with resistance, and when stacked on each other I noticed they had very different curvatures for seemingly identical rings.

Here are some more pictures:

 

[Big Kahuna]

What did the sides of the pistons look like, sounds like a seizure, causing the rings to stick

 

[zpike00eb]

Is the source of all this overheating? The front left pisser was mostly exiting steam or smoke towards the end, and both the head and the pipe would sizzle water. Could water in the cylinder cause the rings to be pushed in? or more likely heat?

 

[tor*p*do]

piston wash is nonexistant on the rear piston
I guess lean seizure toasted this motor

 

[Big Kahuna]

you have had a major seizure........ Not sure where to start with your problems. but you said the base gasket was mushy, that would tell me that either gas was getting to it or water or both...... either way you had a blown base gasket causing all kinds of problems, Lean Seizure, Water Ingestion from blown gasket causing all lubrication to be washed off the piston walls......... Time for a complete top end rebuild, check your crank and seals while you are at it. That is an 20 year old ski.

 

[zpike00eb]

Ok, so what am I looking at, new pistons and rings? What else do I need to get it running again.

What caused it to lean out

Ski is all stock.

 

[zpike00eb]

Also the engine still turns easily

 

[tor*p*do]

with the water intrusion, crank is probably toast
you will need to fully disassemble motor and assess
minimum will be new (next size up) pistons, rings, gaskets, seals and cyclinder bored to new pistons
I suspect also new crank is needed and cases may be damaged
you wont know until you crack the cases

 

[ducesrwld]

you are probably looking at spending 600-700 bucks minimum. find a set of pro-x or wiseco pistons on the top end. check the piston tops see if your top end has original pistons in it or if they are already on an oversize. that's the problem with buying an old ski probably has a lot of original parts still. go the extra distance and get the crank rebuilt for a couple hundred or go out and buy a brand new hotrods crank. nothing worse than spending the dough on the topend then having your crank go on you down the road taking out your whole motor. I've got local guys that can help you out if you are looking for some sources to get this thing back up and running.