400 Scrambler keeps blowing head gaskets
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!