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Discussion Starter · #1 ·
Hello guys, I'm new to this forum, and really to all forums. I recently bought a project mxz600 snowmobile with a bad water pump. I pulled it out and the plastic worm gear was stripped. Installed the new one and refilled coolant. Started it up and ran it for about 10 minutes. Looked like the coolant was circulating because there were bubbles and movement in the reservoir. I topped it off and decided to test ride it on a trail. Got about half a mile and it died with a bunch of coolant splirting everywhere underneath. It didn't seem to have compression after, at least the feel of pulling the crank was too even to have normal compression. I took the engine cover off and one cylinder looked good, tho the other piston was stuck all the way up so I couldn't see the other cylinder. I can't crank it now. Oh, and the spark plugs looked burned, rather than fouled, which makes me think it wasn't getting oil injected in either. Any thoughts? I tried to be as thorough as I could with what I know happened. Here are some things I think could be wrong:
1) the oil pump is stuck, which indirectly caused the water pump to stop and the gear to get rated originally. This would also account for overheating and piston rings melting, etc.
2) the thermostat is broken, so that coolant won't flow, stopping up the oil pump as well, which deprived the engine of oil injection.
3) the original owner got rid of oil injection and depends on mixing oil with gas, and I didn't know this - although I put everything together right, it didn't have oil.
4) I didn't install the water pump correctly and it fucked everything up - lol

Am I on the right track?
Thanks for any help!!!
 

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Whenever you change out a water pump or a hose or a thermostat on a snowmobile you have to purge the air from the system. You have to raise the front end up as high as you can get it with the cap off or if it has a lever pressure cap with the lever up and run it at idle. That way the air can slowly release from the system. Failure to do this can cause overheating, hydrolock and so on.
 

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Discussion Starter · #3 ·
Thanks! I totally didn't purge the air. That's probably the problem then. If it's hydrolocked, what should I do? I'm planning on pulling the top end off and replacing the piston rings but maybe that's not necessary.
 

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Sounds like it overheated and now has damage in it. Going to have to take the cylinder off and find out. I am not a Ski-Doo guy BearAk is so maybe he has more insight
 

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Always mix the first tank of fuel after a rebuild. Very strong chance that multiple issues led to the failure, but the #1 issue would be lack of oil. You can try rocking the crank back and forth to break it loose. However, if you saw coolant on the ground after it stopped, chances are it poked a hole in the crankcase somewhere.


Another possibility is that you had a seal that was leaking into the cylinder that is locked up now. Coolant filled it up and it is hydro-locked. If that has reeds, pull the reeds and look inside.

I do think that any way you look at it, you're pulling the motor apart again.
 

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Discussion Starter · #6 ·
Thanks a lot for the thorough reply. I pulled it apart yesterday and the pistons are ruined. The cylinders are minorly damaged. I'm thinking of sending them to get repaired/bored+honed. Would it be better to just buy everything new?
I'm still not sure if it wasn't getting oil. It could have just been it overheating because I didn't purge the air out of coolant system.
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