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Douglas Motorcycles - General Discussion / Re: Aero 600 Engine re-assembly
« Last post by Aero on 03 May 2019 at 18:52  »
Eric, is there any chance of showing me a pic of what the assembly looks like in front of your timing pinion gear on your crankshaft please?
It seems there should be a spring that loads the generator pinion gear which is missing on my engine & I have no idea what it should look like.

The tappets on mine were definitely the wrong way around & fit just fine in their wrong positions.
This is a pic of the correct orientation, followed by incorrect
Glad if I can help.
As for the tappets, when I disassembled the engine, I was not sure the way the tappets were going but I found out they can fit only one way. (everything being removed from the engine). I tried them both ways and there is a way where they can not slide freely. From what I remember one side is flat and one is round so it can fit just one way.

Let me know if you need anything help. My engine is unfortunately for me still open so I can fortunately for you still make pictures.
Douglas Motorcycles - General Discussion / CW Fork Spindles
« Last post by jasper1912 on 03 May 2019 at 01:42  »
I am in the final throes of dismantling my 1925 CW project with the steering head/forks etc. All reasonably good so far but I seem to have hit a snag with the fork spindles (apart from the challenge of actually prising some of them apart). All the larger threads on the RHS are excellent but most of the smaller threads on the LHS are very poor having been butchered at some stage of their life. Are there any recognised techniques for building up and re-threading or is it a remake situation?

Has anyone ever done a run of new spindles or, indeed, can anyone help me with good used replacements?

Thanks for reading,

Douglas Motorcycles - General Discussion / Re: Aero 600 Engine re-assembly
« Last post by Aero on 02 May 2019 at 21:32  »
Couldn't quite tap the top guide out, as the edge of the barrel was just covering it by a gnats whisker, so took the opportunity to whip the barrels off as I was unsure of the condition anyway.
Inside were fresh +60 pistons, but the rear one had a stuck top ring in it. Pretty certain it was due to slight water ingress as I know the bike had previously stood outside under a tarp for a while & the inside of the cylinderhead was a bit rusty on that pot too.
I can see a weld repair to the crankcases but it looks decent quality. The crank must have been out for that & who knows what catastrophe caused that to crack in the first place so I'm going with Dougs hunch that a later crank was likely substituted in the past.
Hi all,
I am looking for a detachable footbrake mounting for a 1917 attached. Do you have a spare in your shed? Any information will be useful.

Regards Martin
Douglas Motorcycles and Parts Wanted / Fork Spindles for 1920 Douglas
« Last post by lovejoy on 02 May 2019 at 19:03  »
I am looking for a set of Fork spindles for my 1920 Douglas. Does anyone have any spares or is someone making new ones. Any information will be a great help.

Look forward to hearing from you.

Regards Martin
Douglas Motorcycles - General Discussion / Re: Aero 600 Engine re-assembly
« Last post by Doug on 02 May 2019 at 18:03  »

The window in the base of the cylinder should be big enough to knock the tappet guides out without disturbing the cylinders. Nor do you need to completely remove them; just enough that you can wiggle them at a slight angle and slip the tappet free.

Come to think of it, I have seen the existence of a 1936-37 Aero spares book, though I do not have a copy. That would suggest that the 1936-37 models were essentially the same (but no guarantee without seeing the contents). If so, then the change to the oil pump drive must have happened in 1938. Perhaps someone replaced a bad 1936 crank with a good used 1938 unit. No reason I can think of the entire assembly would not interchange. They would need the 1938 timing cover as well, though. Yet I think it was determined from Eric's machine that the change did happen in '37. Not very conclusive, but the moral is there is a high degree of parts interchangeability and you don't know how many times it has been apart and rebuilt in the last eighty plus years.

Douglas popularity was falling off rapidly in the mid- to late thirties. There are far less 1937 Aero 600s than there are '36; and the '38 model is downright rare.


[fix typos. 02May19  Doug]
Douglas Motorcycles - General Discussion / Re: Aero 600 Engine re-assembly
« Last post by Aero on 02 May 2019 at 17:31  »
many thanks for taking the time to share your knowledge. I can see from your picture now that the outer tappets are in the wrong places, and unfortunately after taking the cams out I can see that the inner tappets are also swapped around, which I assume means removing the front cylinder to remove their guides, as they can't be removed otherwise?
By the way my engine is a 36 & same as design as Erics, but near the end of that year, as its a 6/M. I noticed his is a 6L so I guess theres a chance they may have changed to our longer crank nose length & associated parts near the end of 36. My frame is also a 36 as it bears the AE prefix and not the same prefix as the engine as on the 37 models onward.

I'll have to quiz Eric on how the generator gear is tensioned, as it looks like the spring you listed may fit around the spacer that is fitted between the timing gear & coned hub, perhaps pushing that washer into contact with the generator gear so it is forced into the cone.


Douglas Motorcycles - General Discussion / Re: Aero 600 Engine re-assembly
« Last post by Doug on 02 May 2019 at 15:56  »

From the looks of you generator drive arrangement, it would seem you have the 1937-38 type engine. This had the timing side main shaft extend right out to a plain bronze bush in the timing chest. The 1936 models had the main shaft stop short; the oil pump worm idled on its own stud in the timing chest, driven by a face dog (which was also the crank shaft nut). I have a 1936, and it can be seen here:

Forum member Eric S is working on a 1937-38 type; lots of pictures:

I have not seen a handbook for the 1936-38 Aero models, but I do have a 1938 (non-illustrated) spares list. It lists the following:
18307  Timing pinion
18931  Coned hub for generator pinion
18929  Sleeve between coned hub and generator pinion
18944  Spring for generator pinion
18930  Washer for spring
18213  Oil pump work
18309  Key for generator pinion and worm (presumably they mean the cone)
18310  Key for timing pinion
18099   Lock nut
18211  Locking washer.

Presumably the spring is a wave washer, given the restricted space available. Douglas had been using such on the 250/350cc engines to keep the engine rotary breather valve disk against its face, as can be seen here:

I suppose the change from the 1936 to the 1937-38 engine was to reintroduce some sort of slip clutch between the dyno and its drive, as they use to have on earlier models that were driven off the magneto gear. Using a bronze cone to drive is very similar to the friction tapping heads used by machinist in things like radial arm drill presses. Though the proportions do not look very generous.

As for the timing problem, the tappets are installed the wrong way, as you may have already noticed from the image earlier in this post. The faces of the tappet should be vertical. This kept the timing events truly at 180 degrees, even though the tappets are at an angle. Lacking a handbook, I don't have the timing figures for the Aero, but I would be very surprised if they differed much from the 600 EW, which shared the same layout. Figures seen here:


Douglas Motorcycles and Parts Wanted / Re: t6 grips
« Last post by derek morgan on 02 May 2019 at 11:57  »
many thanks Richard and eddie for your reply, had one chrome ring left on handlebar which was solid and came up with the idea of hacksawing the end off of chrome cork screw , hooking the plastic insert out and looks good regards Derek morgan
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