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Yes Tim, it is 7/16" BSF.  BSF and BS Cycle were the usual threads on Mark series machines.


Douglas Motorcycles - General Discussion / MK Anchorage pin front brake thread
« Last post by tck on 19 Jan 2021 at 14:40  »
The Anchorage pin 37558 in my front brake plate has a poor thread where its secured to the link it will clean up with a die and I need a new nut it looks like a 7/16" BSF thread could some kind sole confirm?
Douglas Motorcycles - General Discussion / Re: Dragonfly prototypes
« Last post by eddie on 19 Jan 2021 at 14:34  »
As I understand it, Douglas provided a donor Mk5 machine to Reynolds Engineering, and commissioned them to update the design - basically, this machine was a 'Dragonfly' with a standard Mark engine and gearbox, and wheels. Further development took place and a couple of photos exist of the bike still with a Mark engine, but fitted with coil ignition and an AC generator. (I have a bottom end for such an engine). By mid 1954, Douglas had produced 6 prototype machines (which at a quick glance looked like the Dragonfly) for display at that year's motorcycle show. At that time, they were badged as the 'Dart' - but Douglas were forced to rename them due to that name already being used by another manufacturer. These 6 machines, whilst looking like the Dragonflies we know, were different in many details from the production machines (frames, engines, gearboxes, exhausts, petrol tank, toolbox,  headlight nascelle all being different). Of those 6 machines (engine/frame numbers 1001 - 1006), I believe 3 still exist (one black and silver, and one stone and green) in the Bristol area. The third machine (colour unknown) is somewhere in mid Wales.
  After the show, and before production commenced, more development took place. Filling the engine with oil was awkward, so the filler plug was moved to make it more accessible. Likewise, the carb main jet was difficult to get at, so the carb was set at a slightly steeper angle - which also entailed a modification to the front of the toolbox. The bottom flange of the cylinder barrels had to be cut back to enable them to be removed and clear the frame tubes (without lifting the engine). Tube layout for the pillion footrests was altered, and the exhaust pipes shortened so that the silencers could be mounted more securely, directly to the footrest tubing. Early production machines still retained the 'Douglas' brakes whereas later machines were fitted with 'British Hub' brakes. There were also early and late type gearboxes. Early machines only had a taillight whereas later ones had the luxury of a stoplight.
   As already stated, Douglas exhibited at the 1954 show, but it was a rushed attempt to get a new model in the public eye. Production machines did not emerge until almost half way through 1955 (my early model being at the dealers late July 1955). It is rumoured that within about 18 months actual production had stopped, and machines were being built from the accumulated stock of spares held in the factory. As is now well known, Pride and Clarke bought the majority of the remaining stock when the factory was taken over by the Westinghouse Brake and Signal Company - hence the number of TYP, TYR, ULL and UJJ registrations on the surviving machines.
   Whilst the Dragonfly is not the swiftest thing on 2 wheels, it is one of the most comfortable. Several of us LDMCC members have had great fun competing on our Dragonflies in the ACU National Rally and getting Special Gold Awards for gaining maximum points - one year, gaining those points entailed riding 130 miles to the start, then covering 540 miles on the rally, then another 240+ miles to get back home - a total of about 900 miles from start to finish in 32 hours. It was great fun pitting our sluggish old 350's against the modern plastic rockets (and still beating them to the next checkpoint!). We were certainly a lot fresher than others riding the modern hardware.
  Had the Dragonfly been blessed with a longer development program, it could have been a much improved machine - us owners have had another 60 years to identify (and cure) most of the problems - sadly Douglas were never given that time!


P.S.   From what I have already said, it looks as if your engine (1007/6) could be from the first production machine.  Also, I have heard of several engines being modified to plain bearings - the biggest problem is the low pressure output from the Douglas oilpump - only about 6 - 9 psi.
Douglas Motorcycles - General Discussion / 600 Aero Valve Lifter
« Last post by Hamwic on 19 Jan 2021 at 14:14  »
Hi All,

My 600 Aero has particularly good compression, and the PO warned me about possible damage to the kickstart mechanism, which is known to have its shortcomings. I note from the Pitmans book covering this model that a valve lifter was available as an optional extra. I am designing a mod to go in the original valve chest covers, but does anyone have a machine, with this extra fitted? I'm guessing this could possibly be also used on the 750?

Should your machine have such a thing, a picture or a sketch of the arrangement would be good to see.

Many thanks
Douglas Motorcycles - General Discussion / Re: Dragonfly engine running in.
« Last post by EW-Ron on 19 Jan 2021 at 00:58  »
This subject has been discussed here before.
You should be aware this is an OIL THREAD (!!), and if you ask 1000 folks you will get 1000 different replies.

It is important to note though that the use of any oil inc modern oils is strictly on the proviso that your crank and cases
and oilways have been THOROUGHLY cleaned out and are scrupulously clean.
If you've seen the gunge and old spiders etc that you can sometimes find, you'll know why this comment is important.
Hi Guys thanks for the reply's i will take your advice on board. can anyone recommend a good oil for me to use.
Cheers Kevin..
Douglas Motorcycles - General Discussion / Dragonfly prototypes
« Last post by AndyMorgan on 18 Jan 2021 at 16:07  »
Since selling a pair of Pistons on eBay I have been corresponding with a dear old chap who has taken on my engine cases and crankshaft for an early Dragonfly  6/1007 to rebuild. This had Mk5 barrels and the crankshaft had plane white metal bearings (judging by their condition it is no wonder this wasn't adopted in production). Anyway, he is in the process of rebuilding a number of Dragonflies and is keen to get any information or parts from the prototype machines. Let me know and I will pass it along.   
Hi Ron,
I just realised it's you. Sorry.
Yes, to join the group I must confirm and then you're free to visit.
I must tell you it's all in Spanish anyway but there's a lot of pics of many MkIIIs and spares for sale.
Keep away from any oil that has friction modifiers, thatís most high grade oils today.
OK to use after the engine is run in.
Definitely short bursts of power to bed in the rings.
hi after a complete magnito / dyno for a t35 , im in nth qld
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