In Reply to: 39' engine and fender details posted by Brett (NY) on November 21, 2016 at 15:18:10:
Actually, I think this post is fine right here on the HISTORY forum as you ask some very important technical questions. WELCH (freeze) Plugs were added early on, but like with so many other changes made on the fly with the early 9N, Expansion (freeze/Welch) Plugs are one of those that slipped thru the cracks in parts books and failed to be documented when the change was made. Ditto with the two-ribbed fender rivets. Some have 17 rivets, some have 19. The very first 9N Master Parts Catalog, dated March 15, 1940, lists the Expansion Plugs as p/n 74120-S. When they were added is unknown to me but there is one fella who may know the answers to both of these questions, at least offer an educated guess as to the dates. 9N guru Jason Grooms, who owns at least one 9N and 2N in his collection from every Model Year and is the most knowledgeable person I am privileged to have befriended, may see this and chime in. He frequents the club boards here but rarely posts anymore. He is the one who pointed out to me the different number of rivets on two-ribbed fenders...meantime I will talk to him and see if I can get the scoop and report back. Stay tuned...