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Discussion Starter · #1 ·
I have a chance to buy a 1995 Polaris XCR 600 triple - the piston on the left (I think the guy meant the PTO side) is seized. I'm not an expert mechanic with these 2-strokes - but I think I could handle replacing the piston/rings/pin/bearing - and possibly getting the cylinder fixed if needed (are these nicasiled or cast)- but my biggest concern - How do I find out in the first place what burned it down ? I know enough to look for oil around the PTO seal, check and clean carb and carb boot for holes, also chech float level to spec - but that seems like russian rollet when I then run it - how can I be sure when looking at the damage to know what caused it.
 
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You said check for oil around the PTO. Sounds like you are on the right track. The problem is that when the PTO seal leaks, it leaks air in, and not so much as oil out. Air leaking in will cause a lean run on that cylinder. The thing that takes out the PTO seal are Heat from a miss aligned belt or a bad bearing. The other big thing is belt strings. As the belt comes apart the shredded strings end up around the PTO sometimes and get into the seal. My ski-doo repair manual has a very detailed description of what caused a piston to seize. Maybe your dealer could make a copy of his manual for you to read.

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My 95 xcr did the same Last yr, my left "chaincase" side piston got scored after I went through a bunch of powder and sucked it through the air box and into the cyl and the steam cracked the piston..I had all 3 cyl rebuilt and had it bored for $350. So it could of either been jetting/ plugged jet or some other freak cause..? How do they want for the sled?? They aren't worth to much so make sure you are getting a deal on it.. You can get ones like mine for $1500 around here..
 

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Oh one more thing,once you take the head off you should be able to figure out the cause of the seize once you see the piston, to see if it melted or cracked or whatever..hope this helps some..
 

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If indeed the piston melted down we can pretty much sum up everything by a couple rules of thumb

If the piston is scored above the wrist pin it was due to a lean condition, if it is scored below the wrist pin it was due to lack of lubrication. Also if the plug is still in there, you can check the color of the spark plug insulator for possible lean conditions. Also make sure you've got the correct jets in the carb and the needle jet is in the correct position. I'll take your word for it that it is the piston that is screwed up, but I would also be wondering about the pto crank bearing.
 

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Discussion Starter · #6 ·
OK - how could the PTO bearing cause it to seize ? And how would I determine that ? Would you take the jug off and pull back and forth on the crank to see if there is any play to determine ? I guess the one thing I didn't mention that I guess could have been a cause would be lack of coolent to that cylinder. I guess this would also show up as damage below the wrist pin - like lack of lube damage ? What about a leak down test - Are they hard to do - is it a matter of taking the carbs off and the exhaust off - then taking it to a shop to perform - or is there an easy way to do it at home ? Does it require motor to be removed ?
I sometimes wish I could find a shop that would allow me to "volunteer" time you know - be the "eight-ball" boy [8] just so I could learn a lot of this from being around some more experienced people!
 

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The only way to tell if a crank bearing is gone is to take the crank compleetly out of the moter. XCR 600 motors are very prone to crank problems. I cant tell you how many xcr 600 motors the shop I work at has done and 9 times out of 10 the crank bearings are bad. If I rember right that motor is a mono block, you cant just take one cylinder off.
 

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To check your PTO side bearing, just grab the clutch and lift up on it, if it moves slightly (not solid) the bearing is probably shot. That motor is a mono-block. Also those cylinders are iron, not NiCaSil.
 

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Discussion Starter · #9 ·
Here is a link I found on making a leak-down tester - looks like they talk about ATV and cycles - but I don't see why this wouldn't work to test snowmobile engines .
http://www.macdizzy.com/leakdown.htm
 

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Sportster64 here is a good web site for piston diagnostic. http://eric-gorr.com/tech/pistonguide.html Give it a try Riley
 
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