Improvements relating to Motor-cycle Frames.Patents of Note
02Patent No.: 508,403
Application: Feb. 17, 1938
Complete: Dec. 22, 1938
Accepted: Jun. 30, 1939
George Frederic Halliday- who did so much work on the postwar models- and Aero Engines Ltd are given as inventor for this frame.
That the frame is particularly well adapted to transverse engine arrangements. is the only hint to a power plant configuration. There is no mention in the claim for a push-out rear spindle, though the rear lugs (23) obviously are to accommodate a wheel bearing in the frame as was done on the shaft drive Endeavour and as an option on chain drive big twins of 1935.
Rear forks fittings for use with any kind of wheel bearing may be employed... is all they have to say about it.
...or spring frame attachment may be incorporated therewith if desired. was an added least they rigidly limit themselves.
Except for those rear lugs and minor details, the frame shares many similarities to the concept drawing done by Reg Bryan shown immediately above, and appearing in Eric Brockway’s Book
The Illustrated History of Douglas Motorcycles, page 71. The date given for drawing is May 1, 1939 and so would be of the right time period. The square block engine mounting lugs indicated by (27) bear a strong resemblance. Similar too are the front down tubes broadly sweeping to horizontal. Also what is visible of head stock looks the same. One difference is the seat tube is duplex rather than simplex.
In general the headstock seems to be as used on the postwar models; the
double barrel shotgun top frame tube (11, 12) apparently predates the postwar T35/Mark 1 by a significant amount. The first patents directly related to the prototype post war models (torsion bar suspension) do not appear in Patent Office submissions till 1943.
At first it might be mistaken for the DV60 Ministry of Defense prototypes, but they came much later in 1947. They too had convention rear axle lugs (though described as quickly detachable wheels), with additional differences in twin but splayed top frame tubes, engine mounting via welded on clips (like the T35/Mark series), and a telescopic sprung seat post.
© 2007 D. Kephart, Glen Mills, PA, USA
