Re: 56 Pat Spark Plugs/points

Posted by JWL On 2009/10/22 11:07:20

You have two or three different spark plugs and extreme care should be exercised in how they are used.

Talking only about the Champion brand, the H type plugs (as well as the J type) have shorter threads than the N type plugs. There is a difference in length between the J and H types, but I do not remember which one is longer. This is also true for Autolite and AC spark plugs, but they have their own identification numbers.

Using an H, J, or N type spark plug depends upon the size of the spark plug hole. Not the diameter, but the length. All of these spark plugs are 14mm. I believe the Packard V-8s used J type in 1955 and N type in 1956, but I am not certain.

Long threaded plugs (N type) in short holes designed for H or J type plugs may result in the piston hitting the spark plug, and certainly there will be carbon build up on the exposed spark plug threads in the combustion chambers. Many times these plugs cannot be removed without destroying the threads in the heads.

Short threaded plugs (H and J types) in long holes for the N type will result in carbon build up in the exposed threads in spark plug holes, and the proper longer threaded spark plugs may not be able to be fitted because of the carbon build up in the hole threads.

Check carefully to see which spark plug type should be used. Then there are other considerations: heat range, projected or non-projected type, and resistor or non-resistor. This does not even get into multiple electrode types, and or course the Platinum spark plugs.

Not simple, but not difficult to figure out.