Blowing valve cover gasket 82 xj-650

the bike is an 82 XJ-650 midnight maxim. This whole problem started when I had a stripped spark plug, which I helicoiled. The helicoil got pushed down into the combustion chamber and protruded out into the chamber. when I turned the negine over, the valve hit the helicoil and bent and the piston hit the valve. I then bought a used head with valves that looked good and replaced it. After putting it back together, the valves gapped correctly, I have 150lbs compression in three cylinders, and only 90lbs in the cyllinder that the valve had the problem in. The problem is now, after driving the bike for just a few minutes, the valve cover gasket in the front that seals where there's a gap at the end of the cam shafts where the gasket is thicker, it appears that the front side of the gasket blows out, and the rear part gets sucked in. Not sure if it's compression blow-by or possibly something to do with oil not draining from the valve cover correctly. Any help would be greatly appreciated.

 

I had a similar experience with a spark plug breaking in the head. The valve cover gasket is the same as on my 650 Seca. Did you make sure the mating surfaces were clean and replace the cam end seals?

 

It should be a flat gasket with two half moon seals that are not part of the gasket. Some have the seals incorporated on the gasket. Which do you have?

 

'82 Midnight Max should (if original) have the YICS motor.

The YICS motor uses a rubber gasket with the cam ends built in. It also uses rubber "donuts" to hold the valve cover down. If you're using the old donuts I would suspect these being bad before anything else.