My series 81 spark plug gaskets leak a small amount of compression. Not all of the six but four. I have replaced all plugs and gaskets. One cylinder has had helicoil repair of the spark plug hole, it leaks a small amount also. To check, I put a little soap water and see the bubbles. I’m worried to overtighten and strip threads. Any thoughts?
Ronald. I am having the same problem except, I just blew a spark plug out of the head. In checking the rest of the plugs, I found others where the threads in the aluminum head were badly worn. I think the solution is to have the threads heli-coiled. I will be looking for a company that will do this. I will also need a head gasket if anyone has one. Gasket is McCord #5158, Victor #539 or Fitz #355. Roger Westra
When installing sprak plugs, use the older copper/asbestos type gaskets. Use a new gasket every time. These are available from Olson’s See Parts & Servies Directory. The newer type gaskets require too much torque to get a seal. I use a little high temp anti-sieze compound on the threads, but, not on the bottom two threads. There is a good aircraft type anti-sieze product for this purpose that can be purchased from an aircraft repiar shop at most any airport.
The torque value for 7/8 spark plugs in an aluminum head is 30 ft. lb. Reduce this by 10 percent if the threads are lubricated.