Author Topic: "New 2008 Douglas Doublefly Four" at the 2008 Bristol Show  (Read 8318 times)

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Offline roy

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Hi all, thought you might like to see the "New 2008 Douglas Doublefly Four" on show at Shepton, not sure when it will be available. Roy.



« Last Edit: 08 Jan 2009 at 03:21 by Dave »

Offline bazza

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"New 2008 Douglas Doublefly Four"
« Reply #1 on: 12 Feb 2008 at 18:48 »
Hi RoyChris,Tell us more about about the new 2008 Douglas Doublefly Four.

Bazza

Offline roy

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"New 2008 Douglas Doublefly Four"
« Reply #2 on: 13 Feb 2008 at 09:46 »
Hi bazza, hopefully the production manager "eddie" will be able to give you the details in the near future. Roy.

Offline eddie

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"New 2008 Douglas Doublefly Four"
« Reply #3 on: 13 Feb 2008 at 18:57 »
For LDMCC members - keep your eye on the New Conrod! - an article has been submitted.
                    Eddie.

Offline eddie

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"New 2008 Douglas Doublefly Four"
« Reply #4 on: 03 Mar 2008 at 17:55 »
Hi All,
         For those who are not members of the LDMCC, here is another photo of the 2007 Doublefly. Basically, it is a Dragonfly with a four cylinder engine produced from two Mk 3 engines. The bike is also fitted with more modern wheels and brakes to cope with the extra power and weight.
                                                                    Eddie.

« Last Edit: 03 Mar 2008 at 19:44 by Dave »

Offline eddie

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"New 2008 Douglas Doublefly Four"
« Reply #5 on: 04 Jan 2009 at 10:49 »
Hi All,
         Here is a long overdue progress report on the Doublefly!
        Since showing the bike at the 2008 Bristol Show, I have put about 350 miles on the clock - not a large mileage, but it has shown up a couple of weaknesses. The most noticeable is the temperamental carburation at low engine speeds. The 'H' configuration of the stacked flat twin engine means that the firing sequence either goes round in a square or a figure of 8 (depending on the phasing of the cranks). This means the engine fires twice on one side, then twice on the other, and also that each carburettor gets 2 sucks then a pause, giving rise to rich mixture on the lower cylinders and weak on the top. I tried running the engine with a balance pipe across the manifolds, but the almost constant suction just pulled the slides against the back of the carbs and they wouldn't close. Even without the balance pipe, above 1500 RPM, the engine is very smooth and torquey and the carburation seems to be OK. The easiest solution to the problem will be to fit carbs with butterfly throttles, and run with the balance pipe reinstated. The carbs I have in mind are the Amal 398's that were fitted to the BSA B40 WD model - they have the same flange fitting as the Concentric and the same fuel banjo fitting - just the cables may need altering. If anyone knows the whereabouts of any of these carbs, I would be most interested.
          The second problem that reared it's ugly head is that of rocker gear lubrication. As the engine is a 'four', there is no change of crankcase volume as the pistons rise and fall, so there is no pumping action to push oil mist up the pushrod tunnels to lubricate the valve gear. This first started to show up after about 200 miles - when the engine suddenly became very squeaky. Removing the rocker covers revealed that the tops of the valve stems were dry, and the rubbing action of the rockers had left a brick red, sort of rusty deposit! (like you get from chain links when they dry up). A couple of shots from the oilcan effected a temporary cure, but a more permanent solution would have to be found. The end result is that I have made an auxiliary oil pump that fits inside the timing cover to supply oil direct to the rockers (see attached photo). This pump, driven from one of the camshafts, draws oil from the front of the sump and, via internal piping, feeds it to either side of the timing chest. Fittings through the side of the timing chest then feed it to external pipwork to the cylinder heads. Internal pipes (not shown in photo) then drip oil onto the rockers. Fitting of this pump will have to wait until later as it entails quite a lot of dismantling  - exhausts, carbs, heads, timing cover and petrol tank and headlight assy!
         Whilst this year's mileage has thrown up a couple of problems, it has also given me chance to evaluate other aspects of the bike. Most of the mileage has been done in short bursts, so I haven't had chance to accurately check the fuel consumption, but it doesn't appear to be much thirstier than the standard Dragonfly. When under way, the extra weight is not really noticeable - much on a par with the standard 'Fly, but when coming to standstill, the higher centre of gravity does become apparent. At first, I felt the brakes were adequate - but as they bedded in, I became more familiar with the bike (and was riding it harder) - so the brakes remained adequate. It wasn't until I got back on my standard 'Fly, that I realised just how good those discs were! The Girling shocks that are fitted have better damping than the early generation units originally fitted to the 'Fly, and seem to cope well with the extra weight. When riding, the most noticeable difference between the Doublefly and standard Dragonfly is the rate at which the revs increase and decrease - necessitating a totally different approach if clean gear changes are to be obtained! At the moment, the bog standard clutch seems to be handling the extra power without any problem. With a top gear ratio of 4.7:1, 70 mph cruising is a pleasure - with the engine not sounding at all busy!
                    That's all for now , folks,
                        Have a Happy New Year,
                                            Regards,
                                                   Eddie.

« Last Edit: 08 Jan 2009 at 03:28 by Dave »

Offline eddie

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Re: "New 2008 Douglas Doublefly Four" at the 2008 Bristol Show
« Reply #6 on: 22 Jul 2012 at 14:28 »
Development continues!!!

Since my previous posting I have been experimenting with all sorts of carburation systems. The butterfly throttled carbs from the WD BSA B40 overcame the problem of the throttles sticking open, but proved almost impossible to tune (especially as a pair), and the power was down by a considerable amount. Whilst out on a Vintage Club run, some bright spark suggested the obvious - 'why not fit 4 carbs of the original type?' It was the obvious solution - until you tried to carry it out! Physically, there was enough room, but the cables from the lower carbs would have to go through the upper carbs! As I was still not sure of the outcome, I was reluctant to devote a lot of time to an experiment that may not give any improvement, but as they say 'in for a penny - in for a pound' - there was only one solution - make 4 carb bodies that are canted over at 10 degrees. This allowed the lower throttle cables to clear the upper carbs, but then required 4 float chambers also canted at 10 degrees. As this was still purely experimental, I decided to fabricate the float chambers to keep the costs down - the main bowls being Araldited into the bases. This set up worked well with the carburation now easily tuneable and a reliable tickover obtained at the first attempt. The only remaining problem was that I needed to be Charles Atlas to wind the twistgrip open against the pull of 4 return springs! I figured that as each carb was only of .75" bore and the twistgrip gave about 1.5" of cable movement, I could use a multiplier box (see attached photo) to increase the cable movement at the twistgrip (along with giving a lighter action). With the new carbs fitted, the 'Doublefly' was now living up to expectations and running well - that is, for about 6 months - then I noticed that there was a sign of fuel leakage around the bottom of the float chambers - yes, the dreaded Ethanol was eating it's way into the Araldite. Easily solved, I thought - just dissolve away the remains of the Araldite and have the float chambers welded together. Again, easier said than done - probable contamination from the Araldite resulted in porous welds - so, back to the workshop and manufacture new float chambers from solid.
     At last, fingers crossed, I think we have overcome all the problems, but I guess only time will tell!

    Regards,
                Eddie.



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« Last Edit: 26 Jul 2012 at 18:38 by Dave »

 

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