[JM 35 Sedan]

Old Henry put that special plug in there for a good reason, and it just amazes me that most of the knowledgeable folks here on these engines and those who are in business rebuilding these engines have no clue why that extended diameter is on that special plug. I can remember posting this same question over 10 years ago here on the Fordbarn when Shelly ran this, and no one could tell me for sure back then. I'd put my money on what Big Job is saying.