Amongst a load of parts I recently acquired there is a tram handle, there were 2 things that I didnt realise before.
1. The handle is cast steel because the repro ones seem to be brass
2. It is secured to the shaft with a taper pin which I had never noticed before, is that correct ?


Many Thanks
Marcus

Thanks for that information. The cylinder bore is 60mm so I'm assuming it's a 350cc engine. Plus it goes very well so I think it must be?

They look like 350cc (or 250cc) 1936-37 Aero heads and barrels. The 1934 model Y (250cc) was the first lightweight with flanged exhaust ports, then it and the 350cc in 1935. But according to the catalog illustration, those had a pronounced crowned (convex) shape to the cylinder head fins. The Aeros were nearly flat, and surplus 250-350cc Aero engines are I think more plentiful. I have two 1935 250cc engines and their heads are much like the Aero models, despite the catalog illustration.

-Doug

Is the gearbox still available please? And where abouts are you for collection?

My A31 engine has, apparently, been fitted with later barrels and heads. Can anyone identify which model engine they come from please?
Could they be from a B31?
This engine was said to be rebuilt by Henry Body about 25 years ago.

The front brake for the RA is smaller and of less surface area than at the rear to befit the prevailing practice to avoid having the front tire skid on the loose road surfaces of the time. All that was available in original components to directly measure was a brake arm, the parallel link and its eccentric pin. Curiously, the link had been intentionally bent on an pronounced arc, though a study of period photos showed it was supposed to be straight. The brake arm formed the second link of the parallel motion and provided the correct hole center distance. As for machining new ones, it was fairly conventional work.



Long front brake arm blank, step milled to thickness. The concave ends to the steps is a result of using a face mill, and will be obliterated by subsequent milling.


The blank mounted on its corresponding step fixture. The hold down screws are standard button head hex screws with the head turned back to a cone for more clearance while milling.


First though, a profile cut. I do not seem to have taken a picture of the rough and surfacing steps of the elliptical sections between the bosses.


The fully machined arm, still in the straight condition. As the arm is symmetrical, it simply needed to be flipped over on the fixture to surface the second side.


The bending fixture. Heat is applied and the arm coaxed around the first bend with a hammer and soft aluminum drift. Then the block for the tip of the arm is bolted down to the fixture bed plate and the reverse bend executed. I found that I could not heat and hammer the arm hard up against fixturing to get the correct form. The fixture had to be cut back more so as to go past the point needed to allow for workpiece spring back. This fixture got it close, with some fine tuning at he bench vise to make the offset parallel.


A pair of finished arms with some of the hollow pins the RA used.


After making a batch of six brake arms and doing a trial assembly, a major blunder was discovered. The brake arm copied could not possibly be correct for an RA and a little forethought on my part would have revealed it was too long to line up with the brake cable running down the rear of the fork girder. The correct arm turned out to be (surprise) the same as used on the OB and CW models; though those used a dummy belt rim brake of different diameter. Eccentric pins and studs also appear to be shared between models. The sample I mistook for a RA front brake arm turned out to be a CW rear brake arm. I had machine the longer arm in the straight condition, then bent to the requisite joggle. Not only was that a bit of a pain in the arse, but I had doubt I would be able to pull it off on the shorter arm with its more aggressive bends. So, second time around I machined the arms with the joggle in-situ.



Roughing the steps on the first side from a block. The little triangles along the vise jaws are a form of inserted teeth for gripping the work securely by a very small shoulder. I bit of fancy tooling I was trying out at the time.


Roughing the second side and drilling and reaming the holes.


One blank at each stage for comparison.


Which in turn is bolted to its own custom fixture.


Profile cut.


Rough and finish surfacing cut.


First side done.


Comparison of the long (incorrect) and short brake levers.


Second side needs its own fixture.


Rough and finish surfacing cut.


Before and after, second side.


After heat treatment. Material is 17-4PH stainless steel.


Next were the pivot stud to make. Thread gauges had to be made and shipped globally to the interested parties to test in their girder fork lugs. Half those surveyed used a pitch diameter 0.006" over standard, and one had a pitch diameter 0.003" over standard, the remainder being standard pitch diameter. Why the variation I do not know. The 0.006" certainly seemed excessive for general manufacturing tolerances, and this is the only case I have encountered on a Douglas where there were various 'oversized' threads.


RA front brake anchorage lug with homemade thread gauge inserted.


Some heat treated posts and their nuts & washers. Note back end of post is drilled hollow to save weight.


Group photo.

The front brake arm forms one part of the parallel link mechanism, and a small link forms the second link. This too was milled from solid, in this case using a convenient size of round bar for material. One side was faced just to have a flat surface to work from, and then counterbored in depth to the face of the bosses. The opposing side could have the bosses faced with a face mill cut. Between the bosses needed to be relived as well, and pocketed in. Once profiled, it would no longer be a pocket.


The blank mounted on the fixture. The surfaces for the bosses top and bottom are already cut.


Profiled, and the step between the bosses cut. The step in the fixture to support the work level can now be seen.


Incremental steps. Top and bottom surfaces of the 'blank' and a finished milled link below. The second side of the link requires no further machining as the step down between the bosses was already cut with the pocket seen on the right.


The last step was to turn down the waist of the larger hub, to save a fraction of an ounce. The setup is not shown, but was simply mounting the lever on an arbor in the lathe and reaching in with a hook shaped tool, avoiding collision with the whirling arm of course!

To be continued...

-Doug

QuoteId kill to have a cnc at my disposal, but ill have to keep hacking away at it all manually.

Well you can do a lot with a hacksaw and file. Most of the sculpted shapes here were forgings filed and sanded by hand and eye; likely by an apprentice. They did not need to be a precise surface milled to within 0.001 of an inch. The CNC mill is a convenient tool to do this sort of thing, but admittedly overkill and it could be done without. I still had to sand these by hand with mold & die polishing stones in lieu of additional time machining at a higher fidelity. At some point of diminishing returns it is quicker to stop milling and fettle it by hand.

Do the club spares not have some?

If you have some for sale or can point me in the right direction, I would be very grateful!