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Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by Doug on 14 Jan 2019 at 00:09  »

The original DT solid flywheel had the sprocket threaded to the flywheel with a left-hand thread, and then locked with a right-hand thread ring nut. I sent you a drawing of that in 2010 I think.

There was a late version with a bolt on flywheel to a separate hub, but I think that too used the same screw on sprocket.


Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by Doug on 13 Jan 2019 at 23:52  »

As mentioned, on the exhaust valves of the DT they originally used three springs. #4994 is the 350EW spring that I previously mentioned and it was used as the innermost spring. So technically #10012 should have been labeled the 'intermediate' or middle spring. But it is the inner spring on the inlet valve.

I don't think the valve timing on the exhausts was anymore radical than the inlet, so the purpose of the third spring on the exhaust was (besides wearing out the exhaust lobe quicker!) likely due to the realization that the heat was going to make the exhaust springs degrade in spring rate more quickly. LDMCC members can buy new DT valve springs via the Club. They should also have the EW springs, if you want to go triplex on the exhaust. The road bikes seemed to get by with just the duplex set.

Douglas had another way to combat heat transfer to the valve spring. Underneath the very large flange of the valve guide is a thin insulating mica washer. How effective it actually was, I am not so sure. With the enclosed valve gear models (1932-35) there was a air break between the roof of the port and the floor of the valve spring pocket that probably was more effective. Unfortunately the design also introduced a few new flaws! 

"Superlock Washer" was the term then for what we call a Thackery washer, or double coil washer. Two of the engine mounting bolts I posted a picture of earlier have their super lock washer. The other has a modern single coil lock washer. These are getting hard to find now, as only a few smaller sizes used on fifties and sixties British sports car carburetors seem to be still in production. In the larger sizes you have to keep an eye out for second hand hardware.

Engine breather. This is a small fitting of aluminum and brass that screws into the drive side wall. It vents oil mist onto the primary chain. If the chain breaks, it usually is broken off. The following picture is of a 1934-35 crankcase, but it used the exact same breather. There is a light spring and a sheet metal disk inside that serve as the one-way valve.

Douglas Motorcycles and Parts Wanted / S6 front forks 1930
« Last post by alan reid on 13 Jan 2019 at 19:43  »
Hi I am still looking for S6 front forks,
I have a sound pair of CW or TS front fork legs i am willing to trade, or a sound 1930s petrol tank.
What do you need?
Alan Reid.
I had a look on my bike today, and while it was obscured by the rest of the switch, it looked like there was a crimp ring terminal on the switch and I think it was on position 9. Mine was one of the awful blue insulated crimp variety, but I'll probably replace it with a proper brass ring terminal at some point. Would that be what you're looking for?

Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by Buzzie on 13 Jan 2019 at 16:14  »

Thanks for your latest post. Some more of my worries addressed!

Those crankshaft assembly tests you mention will be very useful. I will certainly check those things,  along with the suggestions you have already mentioned, when I “crack” the crankcase on the first engine. I'm just plucking up the courage. :-)

I have now re visited my parts list check list, and am very pleased to see how many items I have now positively identified with your help. I have still a few things unexplained though.

Cylinder Group

There are two part numbers (4994 and 10012) for the same description - “inner valve springs inlet and exhaust” My cylinder heads both have double valve springs on all four valves.

#7168 is a “superlock washer” on the rocker spindles front and rear. Would this be a spring washer or something more sophisticated?

I'm assuming that #8792  “oil trough front and rear” are the rocker grease reservoirs that feed the wicks in the rockers.


#912 and #766 ball and spring respectively for Non Return Valve. I don't recall seeing that mentioned anywhere in our discussion or elsewhere, or anything like them in any of my crankshafts

Crankcase Breather Group

This group is a complete mystery to me. Obviously pressure would build up in the crankcase, but I can't think where a breather would mount on the crankcase nor have I seen any parts in my collection that could be part of a breather assembly.

Exhaust Lift Mechanism Group

I've decided to do without this Group!

Thanks also for identifying some of the parts in my Mystery Collection. I won't be needing a working Douglas clutch as Buzzie used the clutch in the Norton Gearbox assembly. I just need to find a way of locking the flywheel to the drive sprocket. I will however find the exhaust flange very useful, as I have an exhaust system to fabricate.

 I was wondering about the engine mounting claws. Engine 1 came without any means of clamping it to the frame. I had read something somewhere about engine mounting claws, and when I saw some on ebay I bought them. Engine 2 came with some steel mounting bars, similar to the ones you pictured, which I should be able to use on whichever engine is installed in Buzzie.

Hopefully someone with one of the side valve engines will be able to make use of those foreigners in my collection!

Best wishes
Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by Buzzie on 13 Jan 2019 at 13:14  »
Hi Graeme

Im glad you are finding the thread interesting. Im planning to keep it going so that people can follow the story and learn form it as they build and operate their DT engines.

That's really interesting about your engine, and its BMW crank.  Using that crank could be a way to go, because I am concerned about the reliability of engine no 2 with one of the cranks I have fitted. The two I have left are both a bit grotty, and as Doug has explained my options for refurbishing them to a good standard are somewhat limited.

 I wonder if you have any information about the conversion? What modifications were needed to the crank and to the crankcase? I wonder if he used the BMW conrods or retained the Douglas ones?

I have had a quick look on the internet about these cranks. The good news is that one wouldn't be too hard to find. However I notice the stroke is less than the DT engine stroke (73mm vs 82mm). I reckon this would mean a capacity of just over 440cc for the engine. It did occur to me that the builder might of used 600 or even 750 cc cylinder barrels to bring up the capacity.

Best wishes
Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by Buzzie on 13 Jan 2019 at 12:42  »
Hi Carl

Glad you are enjoying the thread. Doug and Eddie have posted some great stuff and I'm beginning to feel that I might actually get engine no 1 running!!!

Would be fantastic to hear and see some pics something about your project, and the parts you have, what you need to find and what work needs to be carried out  :)

Best wishes

Douglas Motorcycles - General Discussion / Re: 1931 t6 carb
« Last post by DSIM on 13 Jan 2019 at 11:29  »
Ok I guess I'm wrong and Archimedes got it wrongs as well. The float floats by virtue of displacing an amount of petrol that is equal to its mass. That is a fixed level on the float which can be altered by differences in density of the fuel or the mass of the float, (also by the volume of the float a dent perhaps). If the needle valve leaks the petrol level will of course go higher. But the float does not and cannot float higher in the chamber because it has seated into the valve. The large seat on the needle will if in good order give a good shut off with little force. If it was made of a flexible material increasing the force may well improve the sealing but these are brass to brass.  The reason for a needle valve is that the needle presents a small area to the incoming fuel so the level in the petrol tank on a motorcycle has little effect on the level in the float chamber.
 I don't find washers for adjusting fuel level in the Amal list of spares.  Its a reasonable bodge though as long as they don't increase the mass of the float by much.
Douglas Motorcycles - General Discussion / Re: 1931 t6 carb
« Last post by derek morgan on 13 Jan 2019 at 11:22  »
thanks very much to all for all your interest and knowledge, very much appreciated, will keep you updated. regards derek
Douglas Motorcycles - General Discussion / Re: 1931 t6 carb
« Last post by graeme on 13 Jan 2019 at 01:54  »
I agree with Leon
The float will actually float a lot higher in the fuel if the needle didn't shut off the supply; it needs to, to be able to shut it off with any weight on the needle. Like Leon also suggested, I used a fibre washer under the clip to set the level so that the fuel was at the correct level just below the needle jet
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