Author Topic: 1911 5HP Douglas!  (Read 3153 times)

0 Members and 1 Guest are viewing this topic.

Offline Dirt Track

  • Senior Member
  • ***
  • Join Date: May 2004
  • Posts: 212
  • Location: Hobart,Tasmania
1911 5HP Douglas!
« on: 06 Feb 2012 at 10:51 »
G'day all
I was looking through a 1911 bound volume of Motorcycling and spotted a write up on a 5HP Douglas, it looks like no other Douglas. I think it could be a Williamson prototype?
See photos of the bike here.
Howard.



Larger view



Larger view
« Last Edit: 01 Feb 2019 at 02:12 by Doug »

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1654
  • Location: Hampshire, UK
Re: 1911 5HP Douglas!
« Reply #1 on: 06 Feb 2012 at 13:07 »
Hi Howard,
                 What an interesting box of tricks!!! It looks as if it is an OHV? engine with the inlet and exhaust valves facing each other. Russel Newbury used this layout on some of their diesel engines - the inlet valve, port and seat assembly was bolted into the head and could be removed for grinding in the valves without disturbing the head! With the inlet assembly removed, the exhaust valve could be extracted through the vacated inlet port and then ground in and replaced before refitting the inlet assembly. The valve operation also looks to be by pull rods rather than push rods.
         Is there any chance you could post more photos giving the full text that went with the article so that we can glean a little more information?
       Many thanks,
                      Regards,
                                   Eddie.

Offline Dirt Track

  • Senior Member
  • ***
  • Join Date: May 2004
  • Posts: 212
  • Location: Hobart,Tasmania
Re: 1911 5HP Douglas!
« Reply #2 on: 07 Feb 2012 at 06:27 »
G'day Eddie & all.
Here is the 3 page write-up in typical fashion for the day.
It seems the bike had a 2 3/4HP gearbox, they mention the "excellent Douglas forks"....they look like Druids to me! This bike has quite an interesting frame that would certainly puzzle Douglas enthusiasts nowadays if found on the rubbish tip.
I spotted another write-up on a 2 3/4HP model so will make a separate post on that one.
Howard.



Larger view



Larger view



Larger view
« Last Edit: 01 Feb 2019 at 02:12 by Doug »

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1654
  • Location: Hampshire, UK
Re: 1911 5HP Douglas!
« Reply #3 on: 07 Feb 2012 at 10:55 »
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 2'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.

Offline Chris

  • Master Member
  • ****
  • Join Date: Jun 2004
  • Posts: 507
  • Location: Kent, UK.
Re: 1911 5HP Douglas!
« Reply #4 on: 07 Feb 2012 at 11:30 »
Hi all
   When one first examines the two speed gearbox of the 2.3/4 hp model it is surprising just how tiny it is compared with almost any other motorcycle gearbox. In many articles and brochures Douglas described the gearbox as "indestructible". Advertising claims in those days were expected to be taken with a pinch of salt but the fact that it performed well with a machine of over twice the engine size and much heavier coupled with a sidecar and two adults on board does say a lot about their claim. Needless to say they are not indestructible, the bearings are small and have a limited life and often found to be rotating in their housings, the cast in bronze spectacle frames becoming separated from the body castings, huge amounts of end play on the main shaft, rounded off dogs, worn selector fork bushes, teeth stripped from the layshaft gear etc. Nevertheless it was a triumph of design bearing in mind that it was designed over 100 years ago and many are still functioning well.