Old Polaris ATV question

   / Old Polaris ATV question #1  

Oaktree

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I have an early-90s vintage Polaris ATV...350 2 stroke engine. Recently I noticed an oil stain on the ground where I park it. Some investigation showed a small crack in the engine casing, in the area of where the crankshaft would be. Not sure how it happened, I'm guessing I hit something a little too hard while plowing and twisted the frame enough to cause this. Now the likelihood of finding a replacement part like that for a 25 year old ATV is probably between slim and none, and whether it would be worth the expense is questionable. Hate to just junk it though, replacing it isn't really in the budget.

I don't know much about 2 stroke engines, but is this something I can kind of sleaze by with (or maybe in the spring clean it real good and seal the crack with JB Weld or something)? Also, where is the oil coming from? I didn't think 2 strokes had oil in the crank case.

It runs as well as it ever did, so it doesn't appear the crack is affecting compression. Any input would be appreciated.
 
   / Old Polaris ATV question #2  
Clean it up with brake or contact cleaner and put on some high temp silicone on it. Run it til it quits. The oil is from the 2 stroke oil. It is left behind from the combustion to lube the crank. Parts for it will be expensive, difficult to find and labor intensive to split the case.
 
   / Old Polaris ATV question #3  
If it is a Polaris Trail Boss 350 there appears to be lots of parts available on Ebay
 
   / Old Polaris ATV question
  • Thread Starter
#4  
Clean it up with brake or contact cleaner and put on some high temp silicone on it. Run it til it quits. The oil is from the 2 stroke oil. It is left behind from the combustion to lube the crank. Parts for it will be expensive, difficult to find and labor intensive to split the case.

Thanks.
Hi-temp silicone hadn't occurred to me, I'll give it a shot once the weather warms up a bit.
 
   / Old Polaris ATV question #6  
Permatex makes a good one that is copper colored. $6

Depending on the circumstances I'd clean and tough up the case with some 80 grit and JB weld it.,,Silicone has a limited life if it's not secured on both sides..My experience anyway.
 
   / Old Polaris ATV question #7  
Also, where is the oil coming from? I didn't think 2 strokes had oil in the crank
case.

I have never owned or worked on a 2-stroke Polaris (Fuji). But maybe 100s of other
brand 2-strokes.

If you are sure the crack is in the crankcase, then there is probably no oil sump in there.
These ATVs, like 2-stroke motocross bikes DO need to have oil sumps for the tranny
gears, however. Trannies and crankcases are sometimes separate castings, and sometimes
parts of one casting.

There are tons of parts available for these old Polaris', but fixing it properly will require
disassembly, and that will take a lot of time. "Free time", if you DIY.

Also, if the crankcase is cracked, then the engine will not run optimally, if at all. It
needs to be air-tight to properly feed air/fuel into the cylinder.
 
 
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