taping rusted spark plug threads on 1940 JD-B

Thomas MacNaught · May 4, 2011

the threads on block need to be rechased-what size and type tap is used for this?

ErnieD · May 4, 2011

Take an old spark plug and slot the threads with a hack saw. You now have a thread chaser. Put some grease in the slot to catch the debris.

greenmech · May 4, 2011

7/8 -18 it's a special fine thread. Ron Mn

Bob Bancroft · May 4, 2011

I have no experience with a JD B. They're not 18MM ??

Bob Bancroft · May 4, 2011

OK, I just learned something. Talked with one of my elder mechanic authorities and found out there were 7/8" spark plugs!

Anonymous-0 · May 4, 2011

Go to any auto parts store and they will have a double ended tap just for spark plugs. chris