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Douglas Motorcycles - General Discussion / Re: 1931 t6 carb
« Last post by DSIM on 12 Jan 2019 at 22:47  »
Sorry you disagree Leon.
Once the float pushes the needle into the seat and if it shuts off the petrol there can be no more increase in force pushing the float up. The float will not lift until it displaces enough liquid to float it. Once it floats as the petrol level rises the float rises until it stops the flow of incoming petrol. Yes lowering the float will shut off the petrol earlier but the float only weighs a few grams and the addition of washers increases its weight  to which I see you agree.  Dependent on the weight of the washers it may be counterproductive. I did say take the washers out and try first, but setting the level will require knowing where the level is. Amal agree that the level in this type of carb is critical.
Douglas Motorcycles - General Discussion / Re: 1931 t6 carb
« Last post by cardan on 12 Jan 2019 at 22:02  »
Sorry, but I don't agree. The float floats and that's it, and how high it floats is determined by the point at which the needle is pulled (bottom fuel feed) or pushed (top feed) firmly on its seat. At this point the float still has lots of buoyancy and would float higher were it not for the constraint of the needle.

So washers on top are NOT to do with weighting the float down. Washers can, however, be located between the top of the float and the clip on the float needle. This will cause the needle to hit the seat (and shut off the fuel supply) at a lower fuel level - changing the number can help you to find the correct fuel level. Little red fibre washers are good because they won't weight the float down. If the fuel doesn't shut off with a few washers in place (between the top of the float and the needle clip), you'll need to work on your needle and seat. A light lap with Brasso will work unless it is badly worn.

Pity you're not around the corner as I have nothing planned for this afternoon...


Douglas Motorcycles - General Discussion / Re: 1931 t6 carb
« Last post by DSIM on 12 Jan 2019 at 19:52  »
Apologies for an omission in my last message I should have been clearer that the needle I referred to in the last sentence is the needle jet needle. also that I had the same problem with leakage.

The two washers on top of the float make it heavier, which means the petrol level will need to be higher to lift the float. You should start by taking the washers off the float but also make sure the float is very clean, and see if that cures the problem.

I worked out the level in the float chamber by floating the float and needle assembly in petrol, in a suitable glass jar. Then noting the petrol level on the float and marking it.  With the float and needle installed in the float chamber top, in the valve closed position, I measured from the mark on the float to the flange on the float chamber top. This measurement transferred to the float chamber/ carb body gives the petrol level. You can then confirm that this level is correct or make some adjustments to get it right.

The other thing worth noting is that the SG of petrol in the 1930's was probably higher than petrol today (0.72 - 0 .775  for BP Unleaded petrol which includes the ethanol) I would guess that, despite the ethanol, modern fuel has more light ends as the refining process is much more controlled,  however the principle of the float having to displace its own weight to float hasn't altered. That means today the petrol will probably be higher up the float before it lifts it and closes the valve making the possibility of leaking through the main jet higher..
Douglas Motorcycles - General Discussion / Re: 1931 t6 carb
« Last post by derek morgan on 12 Jan 2019 at 11:00  »
many thanks for your reply dsim( sorry I do do not know your name but have you as a buddy now) this is exactly the knowledge I was hoping to receive and will show your reply to mate who should be able to help me out. I rode the bike a few times in the spring and carb seemed fine but the last couple of times the carb leaked without using tickler and she takes ages to start after. as you say over the years carb has been played around with as there are two washers on top of float already . have contacted dick to see if club has any spares for t6 carb and am awaiting reply, again many thanks for your time and interest regards derek
Douglas Motorcycles - General Discussion / Re: 1931 t6 carb
« Last post by graeme on 12 Jan 2019 at 06:51  »
Absolutely spot on - I had to go through the exact same procedure to stop fuel leaking on my S6. I ended up putting a washer on top of the float under the spring clip to lower it.
Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by graeme on 12 Jan 2019 at 06:48  »
Fascinating thread for sure.
Douglas, in thinking about your dilemma in building up the second engine with all the difficulties in refurbishing a crank where the bob weights have come loose, an alternative is to use a modified BMW R60 crank - I know this because this was done in one of the DT engines I own. The work wasn't done by me I might add, but a chap in Australia made several of these cranks in the 1980s
Cheers, Graeme
Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by Doug on 11 Jan 2019 at 17:52  »

The pushrods should only have single springs, one each pushrod. There are two types. The earlier version has a barrel shaped spring and the later a conical spring.

As mentioned these are the same part number as the 350EW valve spring and presumably reflected a change in the supplies for the EW over time. I don’t know exactly when the style changed over but in my mind I arbitrarily place them as ‘tall airbox’ and ‘short airbox’ era. All I know is the one predates the other because the barrel style has the assembly nickel plated and the conical style had the hardware chromed. The later could have been re-plated, but I know the provenance from the early-mid fifties onward and know it has been untouched since then. The LDMCC prewar spares has the 350EW valve springs, but when used as the auxiliary pushrod springs on the DT they rarely need replacing.

On my 1934 OW1, which was a later iteration of the DT engine, I have the exhaust vale lift mechanism but never attached a cable to it. That has about 6.25:1 or 6:5:1 compression and it is not a problem to kickstart; even given the ridiculously high and awkward position of the kickstart lever because the gearbox is up under the saddle.

I have not seen rocker spindle grease reservoirs with that cast tit on them; a new one on me. Some of the TT bikes, and later by individuals copying the TT bikes, had auxiliary oiling to the valve guides. This was by drilling hollow the stud that holds the tappet retaining plate (seen above), and through into the crankcase. Then a banjo and some oil fitting and small copper tubes carried oil mist to the tops side of the cylinder heads and the tubes were pressed into hole drilled through the head and guide. Maybe this was some alternate idea as a source of lubrication supply.  Having said that, the machining of the off-center hole, slot, and cross hole (for a cotter pin?) is really unusual and has be baffled as to purpose.

One other thing you can ‘test’ if you have the crankshaft out is to twirl the conrod around the crankpins. It is natural that they will hunt from side but there should be no tendency for them to thread sideways and bear firmly against the center web or the counterweight. Such helical inclination is a certain indicator of a wracked big end cage.   

Light pitting from rust on the crankpin is acceptable. It is certainly not ideal, but beggars cannot be choosers. Worse is if the surfaces of the crankpin or rod have started to spall or brinell. You can take an oilstone an relive ever so slightly around ‘pothole’ to take the pressure off the edges (assuming the roller will span the defect) but it is always at high risk of more chunks breaking loose and circulating through the rollers and the rest of the engine. If it has started to brinell, there are already ruptures throughout the crankpin between the hard surface skin and the softer underlying core. The heat treatment process Douglas used was rather brutal (water quench on such a large part!) and a side effect was a very abrupt transition between case and core. Don’t lose any sleep over it, they all probably are riddled with cracks! A more gradual transition would have made a stronger interface.

Taper on the crankpins is unusual and was probably a manufacturing fault that has been there since day one. Wear is inevitably elliptical, with of course the worst being in plane with the crank throws due to the inertial and loading of the piston/conrods. As mentioned in the crankshaft post, about all you can do is lap the pins lightly. Grinding them undersize (if you could find anyone to do it) inhibits reassembly.

Given the expected miss-match of counterweights, they all need to be ‘fettled’ to whatever crankshaft the eventually end up residing on. Just as the factory would have done when they originally built them.         

Parts identification.
A)  Bastardized pushrod spring retainer plate.
B)  Part of the clutch release mechanism of the Douglas Flywheel clutch.
C)  Douglas flywheel clutch spring plate.
D)  Some of the Douglas side valve models used cast iron valve guides of this shape, but so did a lot of other things. Not DT unless the flange diameter has been reduced.
E) Looks like it might be the magneto gear from a 350EW. If the face recess has an internal thread just inboard of the teeth, than almost certainly so and for the model with the cone clutch to drive a dyno.
F) Some of the Douglas lightweight side valves had the oil pump worm integral with the engine pinion, like this.
G) Looks like the port flange removed from a DT exhaust system.

By the way, the cast aluminum engine clamps on the table seen in your previous post are the type used on Douglas side valve engines. The originals are a pair of steel bars that spanned the width of the frame. These were plated, though on later road going bikes they were painted black. Despite being steel they are usually bent! The original bolts (three shown) used Thackey type shake proof washers and were drilled for safety wire.

Douglas Motorcycles and Parts Wanted / DT/SW5 Herad Gasket rings
« Last post by Buzzie on 11 Jan 2019 at 15:32  »
has anyone got or know any spare copper headgasket rings for a 500cc Dirt Track / SW Engine?

I need them for a rebuild project that I have underway. It is being discussed on here in this thread

Any leads gratefully received!


Douglas Motorcycles - General Discussion / Re: DT/SW5 Engines
« Last post by carl denton on 11 Jan 2019 at 12:42  »
got to say this is one of the best project if have read on the forum for a long time look forwarded to see how it turns out , it will be of a big help to me as I have got a complete bike to put back together . it was taken apart by a person I did not know over 30 years ago .

yours carl.
Douglas Motorcycles - General Discussion / Re: 1931 t6 carb
« Last post by DSIM on 11 Jan 2019 at 11:00  »
I take it that the carb fitted is the 5/116/S the one with the slide horizontal,   if so the level in the float chamber is critical to starting and running on the pilot jet  The level needs to be JUST BELOW the main jet, too high and it leaks, too low and there are problems pulling fuel through the main jet to start. The pilot jet will only come into play once the engine is running and the throttle is closed. It is possible over the years that various attempts to control leakage by grinding in the needle and seat have reduced the length of the needle and hence the float has to be higher to shut off the petrol which means the petrol level is above the main jet orifice and results in the leak.
Most parts for the carb are readily available with the exception of the needle which is a special because it is shorter but  according to amal drawings can be made by modifying a 5/065 needle. 
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