400 Scrambler keeps blowing head gaskets - Polaris ATV Forum
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post #1 of 4 (permalink) Old 04-13-2010, 07:43 PM Thread Starter
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400 Scrambler keeps blowing head gaskets

Hey all,

My dad just bought a 96 400 2-stroke scrambler 4x4 for my sister to ride, and it is running into some head gasket problems.

He found that the exhaust smelled sweet, and it was pressurizing the cooling system, so he replaced the head gasket. This didn't fix the problem.

He then replaced the gasket again with a copper spray-coating on all surfaces, and this fixed the coolant getting into the cylinder. However, it seems that combustion gas is still getting into the cooling system. If you run the machine for roughly 1 hour, it will blow off the vent line at the neck of the radiator from high pressure.

We are now at the point of getting the head mic'd and machined as necessary. At this point, it has a new head gasket, new radiator cap, and appropriate polaris coolant.

Any helpful hints or ideas on what could be causing this? Are we most likely looking at a head issue?

Any input would be greatly appreciated!
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post #2 of 4 (permalink) Old 04-14-2010, 01:57 PM
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a warped head or top deck sounds logical ,but are you bleeding the cooling system of air using the bleeder bolt in the head. i take it the fan is working properly.
i'm surprised that it will run an hour before getting hot,usually 15-20 minutes ,if there is air getting in the system,and the hot light comes on .
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post #3 of 4 (permalink) Old 04-14-2010, 09:47 PM Thread Starter
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We are using the bleeder bolt (found that useful info on this board!). We are going to get the head and top deck checked, and then figure out if after market parts or simple machining will pan out best.

Thanks for the reply!
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post #4 of 4 (permalink) Old 04-15-2010, 08:30 PM
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the water pump seal may be bad. just something else you may need to check. if the water pump seal goes bad it will turn the little 400 engine case into a compressor and something will give.
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