Some investigations into 2 3/4hp Gearbox vs Engine Serial Numbers
Firstly, a big thankyou to the LDMCC, Len Boydell and the previous Machine Registrars (since the inception of the Douglas Machine Register in 1971) and all the members who have contributed their machine information. Without their efforts my ability to do this research would have been near impossible!
I gave a short introduction to the following work here;
https://www.douglasmotorcycles.net/index.php?topic=9218.0Looking at the 2014 Machine Register I could see that there were some obvious trends in the gearbox vs the frame and engine serial numbers for the 2 ¾ hp machines, but sometimes it was not clear. The records seemingly matching well for some years but not so well for others.
What also became evident from looking at the data, is the number of machines that have been mixed and matched over the years and also possibly incorrect data due to typo’s / serial numbers incorrectly read and recorded. Also, there are a number of machines in the Register where the gearbox serial number has not been recorded.
I plotted a chart of frame serial numbers against engine serial numbers and found that they roughly matched on a fairly obvious trendline (or correlation line as “Cardan” describes it), e.g. the frame numbers are generally in the range of the engine numbers year by year over the manufacturing period of the 2 3/4hp machines. This finding appears to correlate reasonably well with what is documented in the immensely useful The Identifying Old Douglas Motorcycles, thread (Part 1:1907-26 Models 2-3/4hp, 3-1/2 and 4hp
https://www.douglasmotorcycles.net/index.php?topic=488.0) by Doug Cross and Doug Kephart.
Unfortunately, there is no gearbox serial number information given for the 2 3/4hp machines in the versions I looked at (Veteran 3.6 and earlier – since about 2012 or so).
I had a thought that there may be enough information in the 2014 Machine Register to be able to extract some clues about gearbox serial numbers using data that fitted obvious correlation lines. I presume that other people may well have gone down this same path, but a quick search has not revealed any data published on the forum – please let me know if you have any knowledge of previous work as I would be interested to hear about it.
The information I used for this work has been used with permission from the Registrar of the LDMCC. I have no control at all over the accuracy of this information in the LDMCC Machine Register and the following is only my interpretation of that data. Therefore, the following may only give a rough indication of the relationship between gearbox and engine serial numbers for the 2 ¾ hp machines and I cannot accept any responsibility for any errors that may occur through the use of this information for identifying or dating motorcycles or parts thereof. This work is definitely “work in progress” and there is much more research to be done.