What year ? Did they convert from the two valve covers To one valve cover?
10-18-21, according to MTFCA Encyclopedia
Bottom Line Up Front: The conversion ran from Nov 1, 1921 until 3 Apr 1922. Just over 5 months and it near the end of 1921 and the earl part of 1922.
It is seldom ever a single date for any change that was implemented on a Model T Ford. Ford continued to use up older parts. Branches often had the old parts while Highland Park had the newer parts etc. And in the case of the one piece valve cover -- Ford continued to use the two piece valve cover core boxes while converting to the one valve cover core boxes.
In the case of the change over from the two door valve cover engine to the single door valve cover engine we know the first normal production of the single door valve cover engine is documented as starting on Nov 1, 1921 (ref the engine logs which are transcribed in Bruce McCalley's "Model T Ford" book on page 526). And there was overlap with the two door valve cover engines with the last two door valve cover engine produced at the Highland Ford Plant on Apr 3, 1922 (ref: http://www.mtfca.com/encyclo/doc21.htm see Nov 1, 1921 entry as well as page 526 of Bruce's book on the Apr 3, 1922 engine log book). Note a two valve cover engine may have been produced at one of the branch plants after Apr 3, 1922 but not at the main plant. So it was just over 5 months when both styles of engines were produced at the main USA plant. [Note Canadian and English production change over dates may have been different.]
Terry, good reference on the 10-18-21 date. I'm 90% sure you got that from http://www.mtfca.com/encyclo/E.htm#eng2 where it says:
10-18-21 T400D1 [engine block] New design (one valve cover) to be run at a rate of 100 per day.
But you may have missed the note at the top of those engine changes states, "The following dates are those of Ford engineering drawings and do not necessarily indicate the date of the actual change in the part. The change could have been before or after this date." In this case we know they began machining and assembling the one piece valve door engines (complete with transmissions) on 1 Nov, 1921. Approximately 13 days after the date on the factory drawing. Which I believe is actually relatively quick for a change of that magnitude.
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