[Mbraun33]

Hey guys I own a 2002 polaris sportsman 500 that i bought used about a year ago and ive mostly been working on it and not riding a whole lot. Ever since ive had it i always noticed it didnt hold coolant and i suspected i might be in for a head gasket or water pump issue or both but the bike seemed to run fine, i had no external leaks and it never overheated. Just recently after putting it through some hard work i had coolant which has never even come past the minimum line on my overflow that was completely pressurized and shooting out the top of the overflow resevoir cap. I immediately stopped put it in my garage and started taking it apart as i figured it was the head gasket so i have the head out at a shop right now to be planed. I noticed when i took the head off a ton of coolant sitting outside of the cylinder walls. Im assuming this is normal in order to remove heat from the piston rings but im not terribly experienced and not sure. If you guys tell me there should not be coolant there i will be more confident that the head gasket was my problem for sure because i havent really noticed coolant in my oil or the exhaust putting out white smoke so im a little bit baffled. Is there a chance it could be a water pump issue? I havent noticed anything at the weep hole and i dont see how a leak or bad seal could cause it to completely pressurize. Im just not sure what would have caused the head gasket to go on me since ive never overheated this bike with a clogged rad or anything. Any insight from some experienced people would be awesome. Im scared to go ahead and put this all back together and have to rip it up because i should have done something different. Thanks a bunch.

 

[polman500]

It would have been better to do some testing of the cooling system before taking it apart but that is a moot point now.
Can you see any erosion on the old head gasket from the combustion chamber to the water jacket? In my experience it usually occurs at the coolant opening in the gasket on the left front of the cylinder at about the 11 o'clock position looking down from the top as seen in the picture below.
That's usually where I've seen them fail putting combustion pressure from the cylinder into the cooling system.
And yes, there will be coolant all around the perimeter of the cylinder in the water jacket when you take the head off if you didn't drain the coolant from the engine prior to disassembly. If that's the case you should drain it now before trying to put the head and gasket back on. You can do that by removing the flange bolt and sealing washer #'s 5 and 6 on the water pump cover.

 

[latebird]

I've seen many a bad head gasket on the 500 with no visual indication of a failed gasket - leaks compression into the cooling system without leaking coolant into the combustion chamber.

 

[polman500]

I've seen many a bad head gasket on the 500 with no visual indication of a failed gasket - leaks compression into the cooling system without leaking coolant into the combustion chamber.

I agree latebird. I guess it probably depends on how long its been run that way. The ones I've seen will usually have a telltale witness mark where the compression gasses escaped the combustion chamber and pushed past the gasket into water jacket. They will also sometimes have a "water mark" on the cylinder wall at the leak sight where a little coolant seeps back into the cylinder after the engine sits and cools down and residual pressure still inside the cooling system pushes back the other way. Probably not in every case, but I've seen it in some of them.

 

[latebird]

Absolutely correct, but there are some with no visual indication. Strangest one I ran into was a Yamaha WR250R on off road bike. Guy ran it out of oil and needed a new head and cylinder. He opted for a new head from Yamaha but got a big bore kit from Thumper Racing. Big bore kit included a special head gasket from Cometic. The head gasket leaked coolant (Engine Ice) through the gasket material. Cometic said they never heard of the problem. I replaced the gasket and sent the first gasket to Cometic - they had never heard of it happening but ran some tests on it and sent a complementary replacement gasket because it had a defect and while coolant was not entering the combustion chamber it was penetrating the composite material between the liquid passages and the outside of the engine - replacement gasket did not exhibit the same problem.

 

[Mbraun33]

It would have been better to do some testing of the cooling system before taking it apart but that is a moot point now.
Can you see any erosion on the old head gasket from the combustion chamber to the water jacket? In my experience it usually occurs at the coolant opening in the gasket on the left front of the cylinder at about the 11 o'clock position looking down from the top as seen in the picture below.
That's usually where I've seen them fail putting combustion pressure from the cylinder into the cooling system.
And yes, there will be coolant all around the perimeter of the cylinder in the water jacket when you take the head off if you didn't drain the coolant from the engine prior to disassembly. If that's the case you should drain it now before trying to put the head and gasket back on. You can do that by removing the flange bolt and sealing washer #'s 5 and 6 on the water pump cover.
View attachment 147968

View attachment 147964

Thanks for the info. There was some bubbling left on the old head gasket in that spot which led me to believe that it was leaking there but the guy at the machine shop said visuals like that are normal however hes not familiar with these bikes. Im just going to assume that this machine had overheated before i bought it and warped the head. Do you agree? Would it be a safe bet to go ahead and replace the thermostat and rad cap while im this far just in case?

 

[latebird]

I don't agree with a warped head - never seen an aluminum head warp