Exhaust Gasket Need Changing?

shane, I cant speak from experience because I have never owned or worked on a YZ 490 but I can tell you that from working on my past and current bikes, in most cases the exhaust port gasket is a copper crusher gasket which is designed to mold to the pipe and flange of the exhaust port when it heats up. Once it heats up for the first time it takes its shape and forms a tight seal between the pipe and exhaust port. For that reason it is recommended to replace the copper crusher gasket any time you remove the pipe because once you do, you break that seal and it wont be as good as it was when first installed. The ones I have purchased in the past were about $5, but the bikes I was buying them for at the time were not as old as your 82 so parts for your bike may be more expensive due to the difficulty of getting them. Again I wouldnt know. I would replace the rubber o-rings around the circumference of the pipe, as well as the pipe springs, and the gasket all at once. It is worth replacing, especially if it hasnt ever been changed out.

Good reply. I add just a little bit of high temp silcone to the 0-rings on my bikes.

A leak WILL effect performance........like mentioned, use high temp silicone on o-ring/end of pipe area for good seal.