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Old 01-05-2008, 03:17 PM   #1 (permalink)
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Exhaust valve trouble

I have a 2000 polaris 500 XC SP, an d the other day, i started it up to warm it up, and i noticed a rattle, and then about 1 min later, it just went bang and quit.... i tore it apart, and found out that the exhaust valve had actually broken off, and fell inside the engine, causing piston damage, and a whole big deal of dissapointment
is this common, or is this a freakisly remote occurance?. the parts will cost about $500 and im down for two weeks

any advice would be appreciated
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Old 01-05-2008, 03:42 PM   #2 (permalink)
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I've never heard of that happening.
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Old 01-05-2008, 04:07 PM   #3 (permalink)
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well its good to know that it is just a freak occurance, as this is a pricey fix, and the snow here is just beautiful.. yeah the exhaust valve broke off at the spot where it goes from round to flat,and slid down into the engine.thanx
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Old 01-05-2008, 08:13 PM   #4 (permalink)
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That's pretty common on Polaris 800's, less common on the other sizes. On the 800, the original guillotine valves were made of aluminum. When they designed the cylinder to get to 800cc, there was no room for any cooling jacket around the valve, so problems just like you had are common. For a while, they made titanium guillotines, and then stainless steel. That solves the problem. I don't know if they make a stainless for the 500, but if they do and you go stainless, you won't break another one.
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Old 01-06-2008, 11:07 AM   #5 (permalink)
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ccol well i ordered parts already, and im pretty sure it will be a replacement aluminum one, not stainless or titanium, but i will look into it and find out if i can get tit or ss ones.
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Old 01-06-2008, 11:10 AM   #6 (permalink)
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another quick question, what would happen if i just built some plates to cover the exhaust valve holes, and just capped them off, eliminating them alltogether??
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Old 01-06-2008, 02:56 PM   #7 (permalink)
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Porting in a two-stroke is a compromise. You can have a low-rpm ported engine that works really well down in the low RPM range and falls on it's face at high rpm, or a high-rpm ported engine that is crappy down low. Most non-exhaust valve engines are a half-way point; they work ok down low and ok down high, but don't excel at either RPM.

If you defeat the valve, you turn the engine into a high-ported engine. The valve closes the port down at low RPM so it acts like a low-ported engine but as RPM rise, the bellows pushes the valve out of the way to open the ports for optimum performance at high RPM. With the ports wide open, your bottom end will be gone, clutching will be off, probably carb jetting will be off. It could be expensive figuring out those things before you finally get it to run acceptably, and there will not be a whole lot of people anywhere that can give you advice, because not many people have done what you want to do.

Best bet? Fix it, remove the valves occasionally for cleaning and inspection.

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Old 01-06-2008, 04:34 PM   #8 (permalink)
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BC Dan you are one informative dude. great info.
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Old 01-06-2008, 05:19 PM   #9 (permalink)
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Quote:
Originally Posted by harofreak
another quick question, what would happen if i just built some plates to cover the exhaust valve holes, and just capped them off, eliminating them alltogether??
Your engine would have very little power in the low and mid rpm ranges because with exhaust valves they design the porting for high rpm.
If you want to eliminate the hassles of VES, youd be better off to keep an eye out on Ebay for either a non VES 500 XC engine or a crashed 500 XC with a good engine. IMO, the advantages of VES greatly outweight the hassles.
I wouldnt worry about your exhaust valves breaking again. It does happen, but its pretty rare.
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Old 01-06-2008, 08:04 PM   #10 (permalink)
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Like Octane said. If you want a non-VES engine, I'm betting someone with that type of engine will trade you cylinders in a heartbeat because of the advantages of the VES system.
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Old 01-07-2008, 11:42 AM   #11 (permalink)
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right on guys, thanx, my key worry was fixing this same problem again... before the valve broke, it would only rev up to about 7000 for a second or two, (lots of power,) before revving up to 8200(rev limiter? tons of power!!) when it revved out it ran fine, as long as i didnt let off too much, but the throttle response just wasnt there, like it took a second ot two to get max power, then it went awesome. from an idle, it revved up nice, but like from 40-45 mph, and pinned it, there would be that 1-2 second lag before taking off.could this be dirty or plugged valves or a fuel problem?
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Old 01-14-2008, 12:50 PM   #12 (permalink)
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Lightbulb Quite comon .. if!

Hello.

Breaking exhaust valve guillotines can be quite comon if you are running on mineral oil, or some semi-synthetic crap for a good mileage..

Say you use <Brand X> mineral/semi-synthetic for 5000 km, you can be quite sure that you will have to change your guillotines and a piston or two quite soon, or allready have..

The reason is that while running on this type of oil, you are getting a coating of exhaust "debrief"? not sure of the word, but you will get a black coating , that can go up to a few millimeters in thickness , this ofcourse will make your sled perform less, and in the end jam/lock the guillotines, which again may result in a breakoff, or a total fuckup of your engine..

I've seen this happen a lot in norway, especially farmers and reindeer farmers who arent concerned about performance, but good gas mileage and cheap oil.

RUN WITH ORIGINAL SYNTHETIC OIL! VES Gold for Polaris works wonders !

Tip for cleaning guillotines on Polaris:
Screw lose the 2 outermost screws on the valve cap, lift up the guillotines carefully..
Then take a really thin knife/razor and carefully cut off the black dirt off 'em, be careful not to scratch the guillotine itself.. After this, take some carb cleansing fluid and wash them with a sponge with raw surface, when the guillotines are shining, mount 'em back on - now enjoy your ride
Check if there's lots of oil around the guillotinecap when you lift it off, if it's running down the sides of the cylinder when you remove the cap , you should adjust your oil pump slightly lower , a single mm on the marking should do.
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