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Discussion Starter #1
I just got my first ATV so I'm a newbie! I used to run Jeeps but with gas prices an ATV makes more sense.

I bought a 2000 Polaris Sportsman 500. It ran fine when I took it for a spin around the guy’s driveway. When I got it home I greased it all up good and took it for a light duty drive. After about 5 minutes coolant started over flowing from the coolant overflow bottle. It continued for a minute or two after I shut off the machine. I couldn’t tell if it was boiling or bubbles. The coolant is not overfilled. I touched the side of the motor and it was hot but not burn my fingers hot. The temp light did not come one. It's not the fan because it is wired to run all the time. I put my hand in front of the rad with the fan on and I felt a breeze but I think there should be more. It is probably enough to keep it cool though. I opened the rad cap when it was cool and fired up the motor. I can see that the coolant is flowing so it’s not the water pump. As I watched I did notice there are bubbles – with some really large bubbles. This makes me think either it’s airlocked or it’s a headgasket. It looks like the motor was recently out - it’s shiny and the rest of the bike is muddy. What do y’all think?
 

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Welcome to the board!:cowboy:
 

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It does beg a number of questions, like why is the fan wired to run all the time? You say your started it with the radiator cap off once it had cooled and could see coolant flowing. Is there a thermostat in the engine? Is there evidence of coolant in the oil? If you refill the radiator does the engine act like it's hydrolocked (coolant in the cylinder)? Does the exhaust have any smoke or color to it? Have you pulled the plug to examine it? It does sound like a serious problem and I think it's within your rights to ask the PO if he's aware of anything or can explain the clean engine and muddy frame. - MarkC
 

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Discussion Starter #4
I was wrong about the coolant flowing. I rechcecked and it was vibrating enough to trick me into thinking it was flowing.

I see no evidence of coolant in the oil. It never acts like it's hydrolocking. I don't see a colour in the exhaust. I have not got the plug out yet. I asked the previous owner and he hung up on me. He refuses contact.

So I was running it more with the cap off and it continues to bubble. I am certain it's leaking at the head gasket now. I'm going to rip it apart this weekend. Any advice before I take it apart?

Now I've only put about 30 minutes of run time since I got the machine. Mostly idling while trying to find out what's wrong. It recently started a light knock that seems to be coming from the bottom of the motor. I know the idle is not set right. Could this be detonation? Out of timing a bit? I want to just replace the head gasket and set the timing right now but if it's still knocking I'll need to take it apart again. Can I remove the crank case from the cylinder without removing the head from the cylinder?

Thanks!
 

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I know it's "buyer beware" in the real world, but you wish people wouldn't deliberately try and screw you like that. I could never sell something to someone without disclosing what I knew. Yeah, I know I wouldn't make any money, but I'd be able to sleep at night.

I'd go with doing the head first and see what you find. Hopefully nothing is cracked. Make sure the thermostat is good too. Do you have access to a service manual? Perhaps someone here has a PDF they'll offer up. I doubt the knock is detonation or timing. I assume you've checked the oil tank and it at least has sufficient oil. Hopefully, you'll get the head back on and things will settle down. I've not torn down a big single that far, so I can't answer your question about the cylinder and crankcase separation. Good luck. - MarkC
 

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pull the head and try a gasket first, leave the plastic off till you see if that fixes it, if the crank is knocking yoil have to pull the motor ans split the cases to repair, lets hope thats not it
 

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Discussion Starter #7
Why would it not have knocked when I test drove it. That was about 30 minutes of run time ago. Some anti-knock additive maybe?
 

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If it aint flowing I would look at a vapor lock or bubble before the water pump. If you have a bleed screw on the head then open that when filling it. My 400 gave me tons of issues over a bubble. When you run it with the cap on if the return ishot and the intake line aint then it aint flowing. I finaly took a water hose to the intake side and just forced it to flow.

A bad cap will push fluid before over heating as well.

Alot of times you can put it in nuet, take off the rad cap, then wrap the gas. As the compression raises it will preasurize the coolant lines and force it to spit with a bad head gasket. But not always. Some times a preasure test wont even show a bad gasket.

Good luck
 

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Discussion Starter #9
So is there a bleed screw on the head and if so where on the head? I really find it hard to believe that it could be air-locked after running it now for 15-20 minutes with the cap off and constant bubbling. There couldn't have been that much air in the system could there? These are really large bubbles and they continue a minute or two after the machine is shut off.
 

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Well I aint sure if you have a bleeder on a 500. The 400 do. I also dont know how bad they are on vapor locking. But on the 400 I overheated it 4 diffrent times due to the same vapor lock. Bleeder open, let it run forever with the capoff etc... And the 400 is notorious for doing just that.

I only mentioned this because a head gasket dont stop flow. It over pressurizes a system which would push flow not stop it typicly.
 

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Discussion Starter #11
The flow hasn't stopped. It flows fine once it has warmed up and the thermostat is open. It is bubbling constantly though.
 

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Then probly the cap or head gasket like you were thinking. I must have misread sorry about that.
 

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Discussion Starter #13
I did a cooling system pressure test after it was warmed up but the engine was off. I left the system with pressure for a few minutes and I could hear something in the motor. After a few minutes I fired it up to see a bunch of white smoke. Head gasket it is.

Other problems I have noticed. It's super hard to switch between gears. I almost have to punch the shifter. The front wheel bearing on the right side is so bad the tire drags on the tie rod. The seller told me the wheel bearings are perfect. When I turn the handle bars I see that the rivets down on the fram beside the tie rods are loose. I'll drill them out and install bolts.

So basically I need for this machine:
-Carb rebuilt
-All wheel bearings including the one in the front strut
-headgasket
-pull cord mechanism fixed
-tie rods
-all suspention bushings on the a-arms
-brakes
-belt
-speedo sensor
-temperature sensor
-front strut upper pivot balls
-all oils

He told me the only thing wrong with it was brakes.
 

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Thats what you have to watch out for when buying used mach, most are never used but some are trashed and replacment parts are silly expensive. Good luck with it, make sure you take a good look at the axles and 4WD operation also..
 

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Discussion Starter #15
CV Boots are all great. 4x4 works great. I did notice where the u-joint flange slips onto the splined shaft in the front that it it held on with a pin. There is a lot of play between the flange and the splined shaft. Is this normal?
 

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Discussion Starter #16
I got the head off and the head wasn't flat. I'd say the previous owner tried to machine the head himself with an endmill and had no idea what he was doing. I put it on a lapping table at work and I have it nice and smooth now. Hopefully I'll have it running tonight. Hopefully the compression isn't to high now. I have no idea how much he took off.
 
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