Hitchcocks Forum

hi do i use a long or short reach spark plug on my continental gt . in most cases you use long on alloy heads and short on iron. but i have been told to use a short is this correct.
regards mole

Just measure the threads in the head. The electrodes should just protrude past the threads and into the combustion chamber.

The length of the plug thread will be determined by the thickness of the cylinder head at the point where the threaded hole occurs. My 1963 1964 genuine Enfield handbook states for the Continental Lodge 3HN, Champion L5 (previously L10S) or KLG F100. You may need a modern equivalent as some of these numbers are now obsolete. there are many spark plug conversion tables on the interwebbynet. The plug number will determine its "reach. So just look in you handbook or manual and get the right plug, then all will be clear and solved. HTH.

Hi thanks for your help. now sorted it.Did't think about checking the cylinder head spark plug thread length.
regards mole

I got caught out with this once. I have an old two wheel tractor with a Lombardini 10hp motor. I could never get the thing to run correctly and played around with mixture, timing, new plug (with the same type as I had no manual) Finally checked the head and, sure enough some clot had put in a short plug when the engine should have had a long one. I found a site somewhere on the net which gave me the correct plug grade for the engine and all was well. I'm amazed it ran as well as it did with the spark situated 1/2" up the plug hole.