I have just bought a 2003 400ex, it has alot of mods on it 160 main jet yoshi pipe wiesco piston open airbox lid and alot more, but i have a big problem. I have a head gasket leak, not much but its slowly leaking and lightly spraying out at some point and time because i have found what looks like over spray of oil on the engine. I have no idea on how much it has been bored out or what compression im running all i know is that it is strong and has alot of power. Does it sound like a head gasket problem or do i need to use torque my head bolts? Do i need to order a certain kind of head gasket. All i know is that it is not stock and it has been bored. any help will go along way. Also if anyone has a repair manual that would help me out alot since im going to try to do this project myself. Or what would be the cost of someone repairing this for me? Thanks

 

same thing happened to my dvx 400. im getting it fixed tommorrow from a local shop. it would take me forever to do this seeing i have to take everything off the quad just to get the plastic off and the plugs and **** is under the gas tank... and i have school... hopefully its not too much cause i couught it early. but mine when i get to a certin rpm is like gasps for air and bogs down... hopefully its just a new gasket and not a whole top end rebuild

 

The only thing is that it is running great no bogging or anything.

 

How much are they charging you to replace the head gasket?

 

idk. were having them take it for a spin and see what it could be... because we have gotten alot of different possible answers... ill let you all know tommorrow or wed what it is and how much... im hoping not alot cause im broke haha

 

chances are if its a head gasket leak your bike will run lean or have no compression. It could be a rocker box leak or the valve caps leaking. The rocker box has a gasket that is real easy to change.

 

I have found the problem. The long bolts that hold the valve cover on are stripped which is causing a leak on the head.

 

I think you need to install helicoils and new bolts to fix that will involve tearing the motor down. There is 4 nuts that are under the valve cover that hold on the head which is only hold on the valve cover.