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Discussion Starter · #1 ·
I have a 1990 Ski-Doo Safari LX that I got for free from a friend of mine. When I picked it up the engine was not turning, but when I got it home and played with it a bit it started to turn freely. I tried to start it with no success. I tested the engine for compression and found there was none in the left cylinder (sitting on the machine). I have now taken the head off and I found a melted piston [xx(] . The head has melted some and has some foreign material melted into it. The cylinder wall is obviously scored up pretty well. Pictures and the complete story can be found on my website at http://members.truevine.net/[email protected]/skidoopage1.html (sorry about the huge pics). Here come the questions:
1.) What happened (so I can prevent it from happening again once it's fixed)?
2.) Will I need to bore both cylinders to keep balanced? How much should I bore over? Will I need oversized pistons or just oversized rings?
3.) Any chance that I can reuse the head if I clean it up (i.e. sand smooth the melted spots) or will I need a new head?
4.) What else do I need to know to do this? This is the first rebuild I have ever done so I don't know too much.
5.) Any other comments?

Sorry for all the questions, I just don't know much. Any and all comments are appreciated. Thanks so much.
Judson
 

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I had a 90 safari and I also had a cylinder that got scatched up pretty bad. Mine was due to the oiler line breaking and I caught it with only I figure a couple of miles later. Not sure if this could ultimately cause piston to melt or not. This is a fan cooled sled (at least mine was) so it shouldnt be due to overheating unless the fan belt broke. I sold mine but did check on a rebuild and yes you can over bore this quite a bit. You will have to see how bad the cylinder walls are. I know most machine shops will do the boring and cylinder ports for around 35.00 a side. You will have to do both sides. If I remember right the whole top end rebuild including the boring was going to run in the 250.00 range. As far as the head goes, if you can clean it up without scratching anything you should be fine. Is this the 388cc fan?

TXC
 

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Discussion Starter · #3 ·
This is the 447 fan cooled engine. The fan belt is good and the fan spins when cranking. The oil lines appeared to be fine but perhaps the injection system was not getting oil to that cylinder. One thing I noticed was that the good piston had a black film on the top of the piston, while the left one (the bad one) was "clean", this may just be due to the fact that the piston was melted [:I]. Thanks,
Jud
 

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It does sound like that side wasnt getting any oil. I would check for any plugged up lines or fittings and do an oil injection output test before running it with the new top end.
Another thing it could be, but is usually more common with the older sleds, is a bad crank seal. If the seal has gone bad, that side will be leaned out because of the air being sucked in.
Your best bet would be to pull the engine out and replace the seals. Then once you have it rebuilt premix it to make sure it is getting the oil for sure, and then do an oil output test.
Once your sure the injection is working, you should be good to go.
if you want to do it yourself, you'll need a proper clutch puller, and a 3 way puller for the magneto. Get a proper sealant (three-bond or yammabond) to seal the case halves. Your local dealer should be able to get you the seal/gasket set.
Good Luck!
 

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If its running dual carbs, i'd say that the left carb was dirty and you melted down due to a lean condition. Or it could be that the left carb didnt have the right main jet in it. The reason the left cylinder is not covered with carbon is because it was burning so hot it burned it all off. If its a single carb setup, then i would start looking for a bad pto seal or an air leak somewhere. Another possibility would be that the wrong sparkplug heat range was used.
 

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If it was my sled i would replace all seals and gaskets, bore out just one side, new pistons and rings in both, maybe just put oil in the gas and dont use injektion,and i would just sand the head. this i think would work just fine since those engines dont have so much hp..remember to jet the carbs correctly they may be the reason for a lean situation. good luck!!
 

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The melted piston was due to a lean condition. When you run lean, you run hot. When you burn above 1200 degrees, the aluminimum starts to melt. Now, you need to find out why you went lean. This is caused by adidition of more air, or reduction in fuel. Addition of more air can be caused by a faulty carb boot, crcked air box, or a bad crankcase seal. Reduction in fuel can be caused by faulty fuel lines, faulty fuel pump, or dirty or mis-adjusted carbs. On a rebuild, you will need to overbore both cyls, replace both pistons and rings. When you have the cyls bored, talk to them about cleaning up the head. They should be able to hit it enough to clean it, but not take anything off. If they have to shave it slightly, then find about having the other shaved to match. You will need to disassemble the crankcase during the rebuild to check for foreign material and replace the crankcase seals. You will want to look at the crank bearings, as the PTO (Left side sitting the machine) has a tendancy to fail if your clutch is out of balance. When that bearing starts to fail, it allows air to enter the crankcase.
 

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Discussion Starter · #8 ·
Thanks everybody. I will take this to my local shop and see what they think they can do with it. Thanks again,
Jud
 

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yo butter just do the one side and find the air leak or plugged fuel jet. dont let them give you any of that oversell crap of doing both sides. an oversized piston is the same wieght as a stock one. ben there done that![;)]
 

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piston was melted Eh? sounds like gummed up carbs and maybe water in the gas? but then again blewbyyou has good idea the pto side {clutch side}of any engine no matter the make is a good canidate for a leaky crank seal after a major belt blowup.
 

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I had something like that 2yrs back. I lost power and the damn thing would only run on one cylinder.. I went out an tryed starting it 4 a week but it kept running on one cylinder.. changed the plugs messed around.. finally took it in.. My head look almost like that just not as bad.. I still used my same head actually the dealer that did the work said it was fine.. but mine didn't look that bad.. I guess my carb boots had alot of cracks an suxed it alot of air leaned it right out.. but she died on me so i didnt so so much damage plus i only rad it a good 5 feet back to the garage when it started to lose power.. had the whole motor rebuilt after it happened. just in case it was an oil problem.. sleds runs great now.. i tend to lose some power an mes when im in deep snow though.. must be fouling a plug at 4 throttle tryin to move my big butt in deep snow or suxing it snow in the vents cause problems.. Not really sure could be a few things on y it went lean..
 

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Discussion Starter · #12 ·
Wow, way to dig up a grave [:)]. Anyways, thanks for the info, but I already opened the engine up and found bits of piston rings everywhere and other misc crap. I also found that the magneto was broken too. So, I ended up just leaving it in peices and storing it for parts as that is a little beyond what I wanted to try and rebuild. I am now looking for a replacement engine for it, but I also bought another sled which runs (1986 Polaris Sprint 340 F/C), so this sled is on the back-burner waiting for the time when I can find a good deal on a replacement engine.
Judson
 
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