WHAT CAUSES THIS? Polaris 500

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big_bill

New member
What causes the piston to melt in the middle of the top? Cylinder wall not bad, should clean up. This is from a 2002 Polaris 500 Classic Touring around 8500 miles. Changed plugs (BR8Es NGKs)and cleaned carbs, rode 112 miles last Saturday then Sunday got 6 miles and stopped. ????????????????? Any help much appreciated.
Big Bill
 

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trailshredder

Member
big_bill said:
What causes the piston to melt in the middle of the top? Cylinder wall not bad, should clean up. This is from a 2002 Polaris 500 Classic Touring around 8500 miles. Changed plugs (BR8Es NGKs)and cleaned carbs, rode 112 miles last Saturday then Sunday got 6 miles and stopped. ????????????????? Any help much appreciated.
Big Bill
Click to expand...

Lean conditions...could be dirty carbs (main jet partially plugged). Too much air to fuel.
 
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dschultz

New member
More likely the pilot jet than main. Remove the side that burned down and hold it to the light and I would bet its pluged. Did it happen around midrange?
 
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big_bill

New member
My son was riding it and he tends to ride at a steady pace. I just cleaned the carbs, pulled jets, used carb cleaner, always look at the jets at the light. Were all clean. Will be checking carbs, maybe go up a size in pilot jets. Heard that with todays fuel, ethonal and additives, its wise to go to a bigger jet. Always burned premium, mostly BP as I like BP as their premium is clear. Some premiums are a yellow color due to additives, but BP always seem clear. I also posted my Poo 600 1999 touring that also melted down this year, son was also riding that. Its still apart in the garage, guess I'll get that back together this week too, as I am on vacation till March 7th. Thanks for all the feedback.
Big Bill
 
srt20

srt20

Active member
Steady throttle burns down more sleds than anything else. Tell your kid to hammer on it more. Vary the throttle.
 
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trailshredder

Member
dschultz said:
More likely the pilot jet than main. Remove the side that burned down and hold it to the light and I would bet its pluged. Did it happen around midrange?
Click to expand...

Pilot jet is for idle only. Usually when a seal goes out you will see a lean burn down on the exhaust side of the piston. So with a hole in the top of the piston I would concentrate on the carb side. We have also seen this happen because a small ball of ice partially blocks the main. After long snow dust trail rides. Not a lot but it can happen. You said carbs were cleaned....were they put in carb dip???? Spray cleaner doesn't cut it if the carbs are real bad.
 
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booondocker

New member
srt20 said:
Steady throttle burns down more sleds than anything else. Tell your kid to hammer on it more. Vary the throttle.
Click to expand...

Actually, if a carb is not clean, or more accurately there is a lean condition going on, you can sort of supliment to a richer condition by feathering the throttle, which as you migh figure isn't much good for gas mileage, but it can over-come some of the lean condtions. A steady throttle on a well running sled should NEVER cause a melt down by itself.

Manufacturers would be stuck with far more warranty work if steady throttles were discouraged. To get the best mileage, you must use a steady throttle.

As long as you have a well tuned sled, without any of the conditions that can cause a lean burning issue, you should never be worried about a burn down by running at a steady speed.
 
srt20

srt20

Active member
booondocker said:
Actually, if a carb is not clean, or more accurately there is a lean condition going on, you can sort of supliment to a richer condition by feathering the throttle, which as you migh figure isn't much good for gas mileage, but it can over-come some of the lean condtions. A steady throttle on a well running sled should NEVER cause a melt down by itself.

Manufacturers would be stuck with far more warranty work if steady throttles were discouraged. To get the best mileage, you must use a steady throttle.

As long as you have a well tuned sled, without any of the conditions that can cause a lean burning issue, you should never be worried about a burn down by running at a steady speed.
Click to expand...

You must not ride Polaris? Steady throttle burns down sleds, because the manu. make the sleds so lean in the mid-range to meet emissions. Yes I agree, you should be able to hold a steady throttle, but unless you lower the clip on the needles, or get a fuel controller on CFI sleds, you most likely burn a Polaris down holding steady throttle.

You can put a rubber band around a Polaris throttle on Lake Goegbic, they are pig rich on the top end, where EPA doesnt care as much, because who rides WOT all day?

EPA is the issue. But Polaris had to rebuild every 09 800 motor, and have at least 3 different fuel maps.

I know we are talking about a carb'd sled, but this has been going on for a long time, and EPA is the reason for this mess.
 
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snootbiscuit

New member
yep that snow dust and ice in carb scenario is very real! snow goes thru every motor to some degree, on carbs it gets sucked into the vent in venturi. it then sits overnite in bowl, freezes and bam you have the same as a piece of dirt plugging a jet! need to remove carb and take bowl off so u can inspect fuel in that bowl! AND: the pilot is mainly for lower end, but all circuits are flowing at higher speeds, so if its plugged, it could def. lean it out !
 
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Duffy

New member
Timing burns down the center or the wrong spark plug. I don't care if the marks line up, check the timing with a timing light.
 
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doo_dr

New member
Right on the money pr1

polarisrider1 said:
Leaned out. Could be many reasons.
Click to expand...

Hate to beat a dead horse but if you didn't pressure test the motor it could be anything ,and all, of the things listed. Besides pressure testing on a burn down piston motor, I always leave the sled in the cold and pull the carbs. I have seen ice crystals cover all, or part, of the main jet. You do not get to see that on a warm carb and it will answer alot of questions real fast.
 
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raceinsnow

New member
"Pilot jet is for idle only."

The pilot jet is being used from idle to 1/3 throtle and when cruising around at about 4,000to 5,000 rpm and around 20 to 30 mph you are using the pilot jet.
 
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doo_dr

New member
If you look at the ranges that each component covers you will see the mid range has the largest(longest) area of crossover components. The interesting part is that a 2 stroke is trying to "get on the pipe" in this range. Easy guys. Getting on the pipe is the physics that a two stroke will perform best with a portion of the combustion happening out side of the motor while also having a degree of timed back pressure. Think of it a pipe organ at church!!! Anyways this is the range that usually does get the most Holy pistons because the motor wants to get to its optimum running condition and that range is not it. How many remember the dealer telling you to not run WOT for the first tank of fuel and to vary the throttle alot while running 1/2-3/4 throttle. I bet if you think real hard about your driving style compared to the clutching of a stock sled you will find that you seldom ride at a constant 1/2- 3/4 throttle. Don't mix EFI's up with this discussion or it will go way off on a tangent!
 
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