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Blew the top end on my Polaris 550 yesterday.


BillM

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Well the 6-8inches of slush and at least a foot of powder on Lake Joe were too much for my sled yesterday. Was almost back to the truck when I felt the sled lose power.. I had my dad on the back + our Clam Nanook so there was no way I was going to stop.. Ran it on 1cyl for about 100 meters or so and once we got back to the truck.. Wouldn't restart (although it tried) so I knew I had a dead cyl.

 

Got it home and pulled the head + cyl and yup, cylinder closet to the exhaust was completely destroyed.. Blew one half off the piston skirt (I've never seen that before).. Other cylinder looks fine. No metal or anything in the crankcase.. Other then ordering a new piston/gasket kit is there anything else I should be looking at? I know the 03-06 550 fan cooled engines had major problems, but I can't find anything on my '01.. I've tried to search for additional cooling mods I can make to the sled in order for it to run cooler but haven't had much luck. What about header wrap for the exhaust? Perhaps some ducting from the front to cool the engine down a bit more? I've heard about the 550 running lean in the mid range which leads to the engine popping, but again I can't find anything specific to my year, just the 03-06 engines.. Should I maybe run the tank at 100:1 instead of straight gas in order to get around this issue? Again, just looking for some advice, thanks boys!

 

I had to keep the poor thing pinned to stay up on top of the slush, with all that extra weight it just couldn't take it.. I'm just glad it didn't happen out in the middle of the lake, we would have been in really bad shape if we had to walk back the 4+kms to the truck in those conditions.

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I have no advice about the sled, but how was the fishin on Joe? I haven't been up there for years. Headed up for a few days the first week of march.

 

GL with the sled. Its always that cyl that burns up. Not. A lot you can do really. Maybe make two lighter trips? Should be too bad to repair, as long as no junk got in the crankcase.

 

S.

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adding more oil just leans it out more, checking and cleaning of the carb should be a first priority, got pics ?

imo most of theseissues are related to crap fuel don't take much water to blow a fan engine when it's being worked hard.

advice, try www.ontarioconditions.com post some pics and your problem or pm wildbill on that site

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I have no advice about the sled, but how was the fishin on Joe? I haven't been up there for years. Headed up for a few days the first week of march.

 

GL with the sled. Its always that cyl that burns up. Not. A lot you can do really. Maybe make two lighter trips? Should be too bad to repair, as long as no junk got in the crankcase.

 

S.

 

I can't see any visible damage to the crank, so hopefully a new piston + re-hone does the job.. Fishing was good, put 18-20 on the ice, nothing big but a fun day with the oldman..

 

I didn't even think of the sled overheating, 2 trips would have probably been a good idea.

 

ecmilley, appreciate the advice I'll look into that site.

Edited by BillM
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Richen up the mid range will help with the cooling of the engine. Do not add oil as said oil is a lubricant not a coolant. The fuel going into as it flashes has the cooling effect you want. Find all of the pieces before you rebuild there is nothing worse than lunching a new rebuild because you got impatient.

 

 

Art

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Bill check check and recheck before u reassemble, happened to one of our machines, thought we could just replace the piston, looked straight forward, after reassembly found a hairline crack which even a mechanic had not noticed, went on and on, ..............at the end of the day we would have been better off to put a new engine in, hopefully it is just the piston and not bearings bent crank etc.

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Appreciate the advice guys.. I rotated the crank and there's no pieces in the bottom end. From the looks of the mashed up piston most of that skirt is melted to the top/sides of it.. (I'll grab some pics so you'll see what I'm talking about).. I checked the intake/exhaust ports for any damage and there is none. Neighbour also came over to take a look at things (He's a snowmobile guy) and gave it a once over. Said a re-hone and piston and I should be good to go. He's also mentioned something to my oldman about filling the bottom end with oil to get any pieces out we can't see, Once I talk to him in person, I'll figure out what he's actually talking about.

 

I'd love to blow some $$$ on a new sled, but I use this thing maybe 15-20 times a year for icefishing and that's it. I'm not ready to sink $$$ into a sled to let it sit there and collect dust, lol.

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So long as you have it apart, replace the crank bearings and crank seals. Does'nt cost too much more. Check the bottom of the crankcase. This happened to me 2 years ago. I couldnt find the pieces from the piston. Took the whole motor out, and there they were in the belly pan. Bottom of the crankcase there was a loonie size hole i would never have seen unless the motor came out. Certain years of Polaris sleds are known for bad cranks/bearings. Especially the triples. Another word of advise........Don't rebuild the engine on the kitchen table!! The wife does not like that!! (learned the hard way)

Edited by steelhedrmatt
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Possible causes could be, crank seal leaking on that side causing that cylinder to run leaner, or carb issues (if it's not an efi sled) If it's has dual carbs, you could have an air leak at the carb boot on that cylinder or reduced fuel flow due to dirt or icing in that carb. Also check your main jet size to make sure it's the correct size for the elevation and temp range your operating in. If you're mainly running fuel with 10% ethanol, it's usually advisable to increase your main jet size.

 

Also, when you order new pistons, stick with a cast piston like the Polaris OEM or SPI brand. Avoid using a forged type like Wiseco. The forged type are less forgiving if you don't warm up your sled really well before driving it.

Edited by Old Man
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Just curious Bill, how old was the gas, just a thought. Gas has only a 30 day shelf life. Maybe that was the cause??

Mechanic at Bay City told me that old gas will melt your pistons.

 

Gas was 3 days old. I'm not really worried about why it blew up.... . I ran that thing probably 5kms, WOT in 8inches of slush and 1ft of powder doing maybe 30km/h... It overheated I'm 100% certain. I had to make a homemade piston pin puller yesterday to get the piston pin out.. It was in there pretty good.. Got it out however without any problems..

 

Old Man: Thanks for the advice on the replacement piston, I was actually going to order a Wiseco or Vertex (This is what I've used in the past with my 2-stroke dirtbikes).. But I'll stick with OEM or SPI in this case.

 

I'm assuming the numbers imprinted ontop of the piston are related to it's size? (ie standard, .30 over, .50 over) I'm fairly certain it is, I'll have to cross reference that number before I order a new one.

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