Smashed Electrode

[Unregistered]

What would cause the electrode in a properly gapped spark plug (RJ12 gapped at .035) in cylinder #1 to be smashed/compressed to approximately .005?

[Don Moyer]

The intake valves are constantly moving up and down directly below the spark plugs in each cylinder, so I guess we have to allow for the possibility that an intake valve could somehow travel too high and reach the electrode of one of the spark plugs. Possibilities include:

1) The valve spring could have broken in cylinder number 1 which would allow the valve to "float" higher than usual.

2) The valve stem could have broken, which again would allow the top of the valve to fly up and hit the plug.

A compression check should confirm such a failure unless the valve is functioning well enough at starter RPM to give a reasonable check. If you get a good compression check, you may be able to bend a small hook on the end of a coat hanger sized wire and pull up on the intake valve through the spark plug hole in cylinder number one. Without pulling hard enough to cause any damage to the underside of the valve, you should be able to determine if the valve seems loose.

Don