Transmission datecode/design check

[Speeding Big Twin]

Craig, on a 121 35 trans case the earliest date code I’ve seen is from April 38. I wouldn’t be surprised however to find a BT trans case with a March 38 date code because they have been found on some parts such as BT trans lids and Knuckle crankcases.

Notice the position of the lone 2. That position seems to help indicate an early case because when date codes appeared they were placed about where that 2 is and the 2 moved further to the right. Sometimes instead of a lone 2 you’ll find 1.

With five mounting points your case could be as early as mid-37 but I’d need a photo of the R-H side, with the starter cover removed, to see if there is an oil transfer slot or a hole. When the fifth mounting point was introduced, the oil slot was still present. The hole came later.

Regarding cases with casting number 34703 64, some have no date code but some do have them. I have examples of 10 63 (Oct 1963) and 12-63 (Dec 1963) on 34703 64 cases.
Eric

[easykick]

Hello,
I will try to post several photos of three different transmission cases.
Thanks
Mark

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[easykick]

I missed one of the transmissions, I will try to load to it later.

[easykick]

Another transmission

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[1950Panhead]

9 0 is September 1950
E 9 is May 1949
L 4 is November or December 1944

[Speeding Big Twin]

Re the markings on the back of one of the cases, my best guess is they were done by an inspector. A lot of different characters were used there over the years. One of yours looks like an upside down F and I’ve seen it done like that several times before.

I agree 9 0 indicates casting in September 1950.

L 4 indicates casting in December 1944. Sometimes there’s confusion about aluminium date codes (DCs) because the letter I was said to have been skipped at times so it wouldn’t be mistaken for the number 1. This meant by the time they got to December the letter M was being used and this was said to have first occurred in 1948. But it’s more involved than that. For example on some Big Twin aluminium parts cast in 1948 sometimes I and M were both used. And the letter I is found in aluminium DCs on some Flathead parts cast as late as September 1953.

When E and 9 are in an aluminium DC they could indicate casting in May 39 or May 49. Notice the E and 9 are spaced and sometimes there’s a clue in the spacing, or non-spacing, of characters but it doesn’t always work because there were exceptions.
On the R-H side is the insert for the mounting bolt bronze or steel? Bronze would help suggest May 39 while steel would help suggest May 49 because the change from bronze to steel seems to have occurred in late-43 or early-44. However, sometimes there are exceptions to this for one reason or another.
Can you please post a photo of the left side of the E 9 case and also a photo of the top of it. Thanks. And there’s more info via the link below to my DC thread.
Eric



Date codes and other info for some, not all, BT trans cases

[easykick]

Hello,
Here is a better photo of the E9 case, it looks to me like it is a bronze insert on the fifth mounting hole, I hope the picture shows up as so. I will have to get left view and top view sometime later today .
Thanks so much for the information.

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[easykick]

Here are the extra views of the transmission you requested.

[Speeding Big Twin]

Thanks for confirming the insert is bronze. As I mentioned above it helps suggest May 39 as opposed to May 49.

In your photo below notice the bosses at upper left are rounded and they too help indicate May 39 and not May 49. If they were flat then we would have had to investigate further because while a May 49 case would have had those bosses cast flat at the foundry, even a May 39 case could have flat bosses if someone altered them from their original rounded condition.

Another thing I wanted to check was whether or not the vent nipple had a boss and it looks like it does. I’ve seen a boss on May 39 cases before but not yet for April 39. However I don’t know what day it started so it was worth checking your case because if it didn't have a boss then its absence would have suggested May 39 as opposed to May 49.

Anyway, because the bosses at upper left are rounded they help indicate that on this occasion date code E 9 indicates May 39 casting.

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Markings at the back of the case look like an upside down F above S and 40. The 40 is consistent with a case cast in 1939 as opposed to 1949. I’ve even seen that same combo (F, S and 40) before and it was on cases cast in June and September 1939.
Eric