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Discussion Starter #1
I blew up my MXZ 800 two weeks ago and of course it's out of warrenty. The engine lost power and a cloud of smoke came out from under the hood. The spark plug opposite the PTO had aluminum all over it, I was almost if not totally out of fuel. The dealer seems to think it got a couple gulps of air leaning the engine to the point where got so hot it seized, there was plastic melted on the head, thats what the smoke was. I have three questions: Is this possible? Can I just rebuild the top end, pistons, jugs, etc, or do I have replace more? How hard is a top end rebuild, I've rebuild a few dirt bike engines before? Thanks
 

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A top end rebuild isn't that difficult. But If your piston has a hole in it, or is missing pieces, I'd be concerned about debris getting down into the crank case. If thats the fact, you'd have to pull the entire engine, split the case and clean it all out.

If the piston is ok, and just your rings failed, a plain top end rebuild would be sufficent.
 

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Molten metal on the plug...should require a full tear-down. Lucky it is March when this happened, but it is NEVER a good time.

Warranty...I would not think it would cover a gas-out meltdown. But the whole process is not too bad. Also because it is a newer sled, you won't have as many "crusted" bolts and such to deal with.

Let us know what you are going to, and eventually do.

Good Luck,

DNO
 

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Does that mean that if you run your sled to the point that you run out of gas and it stalls that it is bad for it?
 

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Run out of gas = BAD.
 

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Discussion Starter #6
DN036,

Can you expand on your statement? I want to make sure I don't have one of these episodes again!
 

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JohnBoy:

The single most important thing to do for your sled on a regular basis is to make sure the fuel gets to the carbs and cylinders without interruption, ever!

If you get crap in a jet, or gunk up a filter, or even run out of fuel, you will run that cylinder on less fuel than it is suposed to. The fuel cools the cylinder. When you don't have enough fuel, it runs hotter, faster too, but too hot. It will seem to run stronger right before it melts down on you. That's why it is important to know how to check your plugs and stay in touch with your sled.

If you notice somthing different in the way it is running, check the plugs. They will give you most of the end-fuel story. White is too lean, black is too rich, tan is good. There are variations, but this is a good starting point.

Power drain your gas tank every year. Don't just drain it, pump it out, get out all the yuckies. If you rebuild or clean the carbs, you gotta do the whole fuel system. It is a pain in the butt, but you'll be happier if you don't burn up a can. When you disturb the carbs you can jar loose some gunk that can melt you down.

Your plug color will tell you how the thing is firing, and if you need to you can start the set-up running rich and back her down until it works like you want or need it to.

(o;

DNO.
 

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If you run a 2 stroke engine out of gas it creates a very lean condition. Lots of air very little fuel. Everyone has probably heard the engine scream before dying while running a chainsaw, weedwacker, snowblower or other engine our of gas. This is very hard on a high performance snowmobile engine, because the fuel not only keeps the engine running it helps cool it.
 

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if you follow the fuel line from the pump which carb gets its gas first? the farthest one away will run out of gas first. dont kid yourself you may have had a run of the mill meltdown and the mag side allways runs a little hotter something to ponder[xx(]
 

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[br]

It will seem to run stronger right before it melts down on you. That's why it is important to know how to check your plugs and stay in touch with your sled.




Totally right, they run like a bat outta #ell before they blow up, its happened to me 2 times but not in sleds, in odyssey's. So I usually get worried if my sled is a lot faster than yesterday. As for the rebuilding, I would do bottom and top end, one of the times I blew up my 84 250 odyssey, I had a hole the size of a quater in the piston, there was bits if metal everywhere. So if there are bits of metal on your spark plugs, then you need to totally rebuild your motor, you don't want to rebuild the motor and then some loose metal thats still in the motor blows your motor again,

Patrick
 

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Thanks for the info, guys - quality website here!!
I'm going to drag it into the garage tonight to get started. This might seem like a dumb question, but where is a good place to start and what are some of the common mistakes people make when doing a rebuild. I would like to mark / measure as much as possible to find out what caused the meltdown and also make sure it gets put back together correctly, any help would be appreciated.
 

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I had a piston meltdown on my GT 500 a couple of years ago due to leaning with dirt in my jets. When i took it down i had melted the side of the piston at the exhaust port and the ring stuck. All it took was a piston and ring and some acid to clean a little of the piston of the nikasil cylinder and i was back in business for another 5000km. Worked like new and still going with a new owner. The first place to start is to drain your antifreeze, you may be lucky enough to not have to do the bottom end and you do not want to fill it up with antifreeze. If you do not have any pieces from your piston in the base it will be safe to do the top end only. Mark your carbs for PTO side/MAG side because the jetting is different in each carb to compensate for heat. Good Luck.
 

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does your 800 have dpm. W/flatsides? running out of fuel will harm your engine more if it is fully hot or you run WOT. save yourself the pain and remove the motor and top end (for a peek) but have a shop do the rebuild..R/R-ing the motor yourself will save you shop labor $$
 
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