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Douglas Motorcycles - General Discussion / Re: Douglas Aero 1937
« Last post by Doug on Today at 02:33 »

The grooves are deeper and narrower than what the factory used. Someone has modified the center web to work with the 1936-38 oiling system and the spray tree. At least the rod bearings will get oil.

Because the 1936-38 engine uses a spray tree, it does not need to introduce the oil via the end of the crankshaft. That is why the shaft does not need to extend all the way to the timing cover. Nor does the 1936-38 crankshaft require internal oil ways. This probably explains the strange, offset bush in the timing cover. It was part of the modification to install the 1935 crankshaft in a 1936 engine.

The crankshaft stops at the engine pinion nut. The nut has a pair of drive dogs for the oil pump worm. The oil pump worn spins freely on a dowel pin pressed into the timing cover, coaxial with the crankshaft, of course. A picture looking into the timing chest and a view of the inside face of the cover.

Now having said that, I do recall from a prior post that there was some differences noted between the 1936-37 and 1938 engines. Specifically, the 1938 engine the worn has a key. In my engine, no key is required. So perhaps they did extend the timing shaft back to the timing chest, though I am not sure why they would bother. They had a lot of other engines with the 'short' shaft and they never seem to have been a problem. I have a 1938 spares list, but while I have seen the 1936-37 spares list, I do not have a copy of it.

As I mentioned, typically there is no shims or bearing spacers on the timing side of the crankshaft, but again, perhaps this was a requirement of using a different crankshaft in the crankcases.

You probably will not find tab washers the right size. It is a small bolt diameter with a large hex head; an unusual combination. Most likely you will need to make them.

The aluminum cages in the photo I used are the roller bearing cages for the connecting rods.

Douglas Motorcycles - General Discussion / Re: Douglas Aero 1937
« Last post by Eric S on Yesterday at 18:03 »

The center web has well the oil grooves machined.

As for the play in the middle bearing, It looks like the shaft bears on the aluminium frame, look at the marks on the shaft. So that's where it pivots around.
Bearings measured with a caliper at 24.9mm, shaft measured at 25mm. So considering mesuring internals with a caliper is not accurate it is a good fit.
So it should not pivot???

THe pictures shows the shaft entering the bearing but not in place yet.
Shaft is much longer than on your picture. However how would the short 1936 shaft would fill the difference in length?

I have not removed the nuts yet but I don't think I have lock washers? Where can I get them?

What are those aluminium cages on your picture?
Douglas Motorcycles - General Discussion / Re: Douglas Aero 1937
« Last post by Doug on Yesterday at 16:41 »

Sounds like the oil pump and the spray tree/bar is o.k. However if the center web of the crank does not have the shallow grooves, the oil is not going to be able to get into the connecting rod bearings as it ought to.

You will need to be more specific about the clearance in the 'middle' bearing. Is the play in the bearing itself, that is between the inner and outer race? Or is the play in the fit between the bearing and the journal of the crankshaft? Either way, it needs more investigation as it sound like something is amiss.

The long timing side shaft, apparent lack of oil grooves on the center web, and mention of a 'middle bearing' (implying there are three) make me think you have a 1935 crankshaft in a 1936 engine. Have a look again at the photo I posted of my 1936 crankshaft. Note the timing side shaft is short. It ends at the nut for the timing pinon.

Also it contains the answer to your question about crank pin bolt retention. There are supposed to be a tab washer under the bolt head.

1. Marks of the heads of the tappet adjuster from the tip of the valve stem. Normal.
2. Make a new washer, but keep the outer diameter smaller than the root of the gear teeth. The spare list does not say how thick the washer should be. So copy what you have, or try to figure out what the optimal thickness would be to bring the face of the pinion flush with the rest of the gear train.
3. See above.
4. Simplest answer is that piston (and rings) were passing more oil than the other. Be it scoring in the cylinder, rings tired, excessive ring gap, ring flutter, or all the many things that lead to excessive amounts of oil getting past. De-coking engines was a fairly regular ritual back in the day. We are rather spoilt by modern engine in comparison with better air filtration, lack of dusty roads, and lower mileage on vintage machinery as to expect never to do need to scrape carbon. Having said that, both pistons should carbon up at about the same rate.
5. Yes.
6. The aluminum seems to have been 'smoothed-off' at the factory. Or at least in the areas where readily accessible; they did no go into every nook and cranny. Nor did they bother on areas not readily visible, such as underneath. I don't think it was polished to a mirror reflection, more of a satin finish. Most likely it was a job given to the apprentices, so the amount and diligence likely varied from motorcycle to motorcycle. As previously mentioned and shown in the adverts, much of the timing side face of the engine was painted black.

Douglas Motorcycles - General Discussion / Re: Douglas Aero 1937
« Last post by Eric S on Yesterday at 15:28 »
I went and checked some details.
- The tree is well adjusted. 2 ports are facing right on each edge of the center web.
- Bearings are turning smooth with no play I can feel.
- Same for Conrods. Only a little barely feelable axial play.
- Tested the oil pump. Oil fed through the bottom port went down through the bottom plug. Then I put oil on the top port and turned pump the other way and oil dropped from the tree.
So I guess it's a pass.
- Checked play on the crankshaft :
   - No play on Flywheel bearing
   - LARGE play on the middle bearing like several millimeters
   - When crankshaft is sled through BOTH bearings, absolutley no play I can feel (see picture below)
   - When oil pump end is fitted, no play either of course.

Now some questions.
1. I made pictures of the marks that tappets are making on the valves. Is the pattern normal or does it tell anything?
2. What shall I do with this homemade washer. Should I make a plain washer of the same thickness?
3. How to lock the big nuts on the crankshaft? Loctite is required and is it enough?
4. I have more carbon on top of 1 cylinder than the other one. Any meaning?
5. Can I sand blast cylinders to paint them?
6. What was the finish on the aluminium parts? Polished, blasted, brushed?

Douglas Motorcycles - General Discussion / Re: 2 3/4 oil capacity
« Last post by Eric S on 19 Oct 2018 at 06:58  »

OK I thought I would have to kind of preload some oil in there to lubricate before the oil under pressure makes it there.
Thanks Richard, I've gotten in touch with Pete, those are some really nice looking levers.
Douglas Motorcycles - General Discussion / Re: Douglas Aero 1937
« Last post by Doug on 17 Oct 2018 at 23:43  »

Original 1936 Aero 600 oil lines.

Somewhere I should have the fuel line, but I cannot lay my hands on it at the moment.

While the following advert dates to 1937, it shows a 600 Aero in the 1936 petrol tank scheme so must be a left over model.

Pride & Clarke were advertising the Douglas line as early as April 30th 1936 issue of The Motor Cycle.


Douglas Motorcycles - General Discussion / Re: Douglas Aero 1937
« Last post by Doug on 17 Oct 2018 at 22:58  »

The slotted screw on the center web of the crankshaft is a plug for an oil gallery. The 1936 Aero engine was derived from the 1935 500cc "Blue Chief" 500cc Douglas. The Blue Chief had a drilled crankshaft and oil pressure feed to the end on the crankshaft on the timing side. I would appear you have a Blue Chief crankshaft in your Aero. If so, the crank does not have the shallow grooves leading to the connecting rod bearings and the spray bar oiling is not going to lubricate the big end bearings correctly.

The tappet chest covers, dynamo, and entire intake manifold were painted black. No bare aluminum. The copper hot air tube for the carburetor is a facsimile of the original, which was chrome plated steel. The end had a small flare. It extended to the top of the cylinder head, not past it.

The oil lines did have a short segment of flexible hose. The original furrels are a little more rounded on the ends than modern ones. The rubber was not black, but a blue-grey color.

This must have been something common at the time, because the handlebar grips exhibit the same blue-grey color. Note the ends where the grip was protected from the elements:


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