Thanks Howard,
From the write up and the fact the bike has no identifying marks, I guess this was a development machine used for testing. It is interesting to note that engine has spark plugs in the underside of the combustion chambers (alongside the barrels) and unlike the 2¾'s, had twin cams to operate the pull rods. With these deviations from contemporary Douglas design and the lack of identifying marks, could this engine be laying unrecognised in someone's collection of spares? The reason I ask is that, in my spares, I have 2 sets of crankcases for later models that do not fall comfortably into the accepted slots for Douglas machines, so presumably are prototypes that never went into production.
Eric Brockway's book illustrates a Reg Bryant design for a road bike dated May 1939, which has heads and barrels to the same design as the generator engine. I was discussing this with another LDMCC member when he suddenly announced "I think I've got those crankcases - do you want them?" The result is that I am now trying to build a replica to that design. What is interesting about the cases is that they are obviously akin to the Mark series cases but have many detail differences - but there are no identifying marks, not even an engine number! The only mark that I have found is a "1" stamped inside the timing chest (probably, then, the original prototype?)
Moving on a few years, during the development of the Dragonfly, Renolds Tubes/Ernie Earles were given the remit to update the Mark design. The first prototype had all the Mark 5 mechanics mounted in the new cycle parts. Later versions showed a similar motor but with the mag replaced by coil ignition (along with an annotation that the engine was a wooden mock up - but was it?) The 2nd set of crankcases that I have are obviously related to the Mark series but the front half is extensively modified to take a distributor (possibly with auto advance), a built in oil filter (like the Dragonfly), and oil fed through the timing chest to the nose of the crank (again, as on the Dragonfly).
The common factor about these cases is that they don't carry any marks, so, to the layman, probably can't be identified. This now begs the question "How many other 'slightly odd' motors are laying, in isolation, unidentified, in member's collections?"
If there is sufficient response, I am prepared to set up a register of these 'oddities' so that we can better identify the design sequence of our machines. Legend has it that the generator engine spawned the postwar motorcycle engine but that 1939 design predates the 1942 generator engine, so does that now blow that theory out of the (muddied) water?
Regards,
Eddie.
