Author Topic: Douglas Aero 1937  (Read 36061 times)

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Offline Eric S

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Re: Douglas Aero 1937
« Reply #200 on: 23 Oct 2018 at 09:02 »
Doug

it is confusing what this bike is. Some kind of Frankenstein's bike maybe.
In any case my main concern is to have it back on the road now.

I considered checking with a local company to repair the cone on the flywheel and crankshaft but I did not had a chance to visit them yet.
In the meantime I was wondering if I should check with a UK based company that may be more used to this kind of work. If anybody has an address to share?
« Last Edit: 23 Oct 2018 at 14:55 by Eric S »

Offline Doug

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Re: Douglas Aero 1937
« Reply #201 on: 23 Oct 2018 at 15:58 »
Eric,

Douglas changed a only a little bit from one year to the next year (most of the time), so there is a lot of parts interchangeability between years.

I was thinking some more on your description of play in the one crankshaft bearing. Douglas typically used a double row self-aligning bearing on the flywheel side.



It looks like they continued this practice into the Aero models, judging by what I took out of mine. If so, then being able to swivel the crankshaft around prior to it engaging the second ball bearing is normal. While you still can get the double row, self-aligning ball bearings, it is much more durable to use double row, self-aligning roller bearings. Those were not available back in the day, but it is what I use today in my Douglas engines.

I think the theory for using the self aligning bearings was Douglas knew the crankshaft was going to whip about. Rather than try to resist it and perhaps crack the lightly constructed drive side crankcase wall, they allowed the crankshaft some freedom under the assumption it was more likely to spring back!

Welding up of the taper on the ohv Douglas crankshafts has not always been successful. They tend to break where the weld stops. However, the side valve motors produce significantly less power, so it is probably worth trying.

-Doug


[Fix typo. 23oct18. -Doug]
« Last Edit: 23 Oct 2018 at 21:50 by Doug »

Offline Eric S

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Re: Douglas Aero 1937
« Reply #202 on: 23 Oct 2018 at 17:01 »
Doug

the plan was to check again this bearing after work so your message arrived right in time.
I used a piece of metal that slide just tight in the bearing and there is well a side play induced within the bearing. Of course it does not move as much as in your illustration and shouldn't you post this note, I would have said I had a problem with the bearing.
When the shaft is in place, it does touch the aluminium frame only when the shaft is pushed from side to side.
Considering the marks I have on the shaft, I would say the shaft does not turn true, the "self-aligning bearing" does his job and the shaft rubs against the aluminium and makes this small shiny mark.
We should be fine there too?!?

As for the tapet chest covers, the parts I have are chromed (should be black) and they are plain steel, like 1/8" thick. Are they the right parts? Gaskets are made of some kind of rubber and are the same size as the cover. Being held in place with just 1 screw, I can not see how a circumference gasket could make it.

Is there a relation between the loose crankshaft and the shattered cone on the flywheel?

Now to summarise the situation

1. I need to make tab washers for the nuts. I will double this with Loctite.
2. Need an adress to adress the flywheel cone or I will go locally
3. Will try to make a new washer to replace this strange washer I have behind the timing pinion. Isn't it an oil slinger there too?
4. Source engine head bolts. The only one I found for now are those below 5./16W -18 Tpi

« Last Edit: 23 Oct 2018 at 17:20 by Eric S »

Offline Jonathan Hewitt

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Re: Douglas Aero 1937
« Reply #203 on: 23 Oct 2018 at 20:13 »
Good evening all ,I have been watching with interest. How much metal needs putting back on the taper and is the crank material suitable for hard chroming and then grinding. I have had small marine gearbox output shafts done this way ie 1 1/4 " dia   over a length of 3". just a thought
Jonathan

Offline Bob M

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Re: Douglas Aero 1937
« Reply #204 on: 24 Oct 2018 at 03:06 »
I've also had gear box shafts built up with an electroless nickel process and found it satisfactory. They required I grind the shaft well undersize to the necessary surface finish first and they then built it back up to size using their process with no further work required by me. I was impressed by the precision of the process.
 
I suppose what Jonathan and I are saying Eric is that there are other ways of repairing the crankshaft taper which do not necessarily involve welding. It's worth checking them all out.

Unfortunately I've never yet found a system that doesn't require the firm application of a thick wad of cash to to get a result.

Offline Doug

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Re: Douglas Aero 1937
« Reply #205 on: 24 Oct 2018 at 04:09 »
Hard chromium electroplate (versus decorative chromium electroplate) has been used on DT crankshaft tapers with poor results by the late Phil Manzano. Eventually the crankshaft broke at the top of the taper where the plating stopped. It is impossible to ask now if the crank had been baked to minimize hydrogen embrittlement resulting from the electroplating process, though I would have though Phil to be aware of that with his engineering background. At the time it was felt to be a combination of a stress riser where the plating stopped, and well as the very low coefficient of friction that the chromium plated surface had. This low surface friction made it impossible to stop the flywheel from 'shimmying' slightly on the taper even though the joint was lapped, and the added shock loading may have contributed to the premature demise of the crankshaft.

But as mentioned before, the power of the 600 Aero is no anything like a tuned DT, so plating (or welding) may well be o.k. But if you do go with plating, make sure the firm doing the job takes steps to minimize hydrogen embrittlement. If they have plated springs and other hightly stressed parts, they probably already know all about it.

-Doug

[fix typo. 25Oct18 -Doug]
« Last Edit: 25 Oct 2018 at 18:50 by Doug »

Offline Doug

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Re: Douglas Aero 1937
« Reply #206 on: 24 Oct 2018 at 06:20 »
Eric,

The tappet chest covers are aluminum castings-



They are flat on the outer face, but there is a raised boss where the bolt passes through. Also, the edges are well radiused. On the inside they are ribbed. Notice also, even though the inner face is recessed, there is some light milling to make sure the head of the tapper adjuster screw does not touch the cover (on the left side).

The original bolt will have a very small Kingswood trademark, unless it has been polished away.



I have an old stock gasket set, but I do not know who the manufacturer is, or how accurate the material thicknesses are. But the gaskets for the tappet chest covers is a thick pasteboard type material, 0.070" thick. The gasket abuts the crankcase on one side, so rotation is not a problem. Yet it could slide downward, but I guess it was expected to stay tight. After a short while, the gasket probably deformed to the edge of the cylinder casting and that helped keep it in place. Perhaps the factory gasket had a horizontal crossbar across the middle with a hole for the bolt that kept the gasket from dropping down and these aftermarket gaskets I have are a cheap replacement?





I looked in the 1938 spare list and they do call out an oil slinger for both the flywheel and timing side ball bearings.

The self-aligning bearing is to allow the crank to flex at elevated rpm, but the main journals should run true. The self-aligning properties are not to accommodate a bent crankshaft. If the crankshaft is bent, the rod bearings are going to have a tough time and you will also likely experience piston seizures due to the pistons being crooked in the bores and developing hot spots.

I made new cylinder head bolts for my engine. Actually I made them several times over. The originals were quite rusty, so I decided to make new ones in polished stainless steel some twenty-five years ago when I first got my '36 Aero. The place I just started working at the time had a CNC lathe and specialized in stainless steel parts. So I made some out of 304 grade stainless, as I did not think the original bolts were made out of anything special regarding strenght. When I tightened the bolts, I noticed they never did pull up tight but just kept turning, and turning , and turning... I took the bolt back out and the 5/16-18 Whitworth thread was 5/16-16 pitch where the thread exited the tapped hole! :( I had underestimated the small (and weak) core diameter of the coarse Whitworth thread. Fortunately it did not mess up the thread in the cylinder.  So I made new bolts out of 420 stainless steel and had the fella at work ruin them through the heat treat furnace. Those ended up so hard they were brittle, and the heads popped off one after the other. :( I suppose the fella could have heat treated them to a lower hardness, but he only knew one process for each grade alloy and for 420 it was dead hard all the way through! Finally I made them out of 17-4PH stainless, which can be heat treated without getting too hard and brittle (about 46 HRc). I don't think the original bolts were plated, I would have to search them out and check.

Recently I made some for my F28 (1928 600EW) that are also 5/16-18, but a different shape to the head altogether.



There may be a relation between the loose crankshaft and the torn taper. If the crankshaft is jerking about the flywheel is going to be jarred and that will only encourage it to become loose on the taper. However, a poorly fitted taper is sufficient in itself to work loose and start fretting and scoring the surface. Mind you, a loose crankshaft is a catastrophe just waiting to happen.

-Doug

[Strike out comment about tappet adjuster clearance, see subsequent post. 24Oct18 -Doug]


« Last Edit: 24 Oct 2018 at 09:05 by Doug »

Offline Doug

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Re: Douglas Aero 1937
« Reply #207 on: 24 Oct 2018 at 09:03 »
When reinstalling the tappet covers I noticed that the heads of the adjuster screw do not even come close to the joint surface. So why the one tappet cover has a little extra clearance milled on the inner face, have no idea. Previous post edited.

-Doug

Offline Eric S

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Re: Douglas Aero 1937
« Reply #208 on: 25 Oct 2018 at 16:59 »
Using the enclosed set up I measured the crankshaft for trueness.
Results are not exacts due to my ability to measure and the condition of my lathe.
A = .005-.007
B = .009 - .015
C = .009 - .013
D = .005 - .007
E = .005

Is that good enough or not?
I did not applied too much of a pressure to hold the shaft although when I did it I did not paid attention to that...
« Last Edit: 25 Oct 2018 at 17:28 by Eric S »

Offline Doug

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Re: Douglas Aero 1937
« Reply #209 on: 26 Oct 2018 at 04:15 »
Eric,

It is impossible to say with that setup. You do not know if you are reading run-out of the crankshaft, or run-out of your mounting in the chuck or the tailstock center; or a combination of all the above. Three-jaw chucks are notorious for not being very accurate. You would need to get the chuck and the tailstock ends indicating zero run-out for the values at A through E to be directly meaningful.

If you were able to get each end running true, the typical number often quoted for two-bearing motorcycle crankshafts (usually single-cylinder engines with full dish crankshafts) is no more than 0.002 inch total indicator reading at the bearing journals.

I have not seen a factory value specified for Douglases. They only stated "Return the crankshaft to the Works for service"!
-Doug

Offline Eric S

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Re: Douglas Aero 1937
« Reply #210 on: 10 Nov 2018 at 19:07 »
Hello

today saturday 11/10 I went to the Epoqu'auto show in Lyon, close to home.
I met there several companies that could repair the cone on the flywheel/crankshaft.
One young chap seemed to me to be more inclined to make a good work.
He owns a company making general machining and just set up a new company to build pinions and he's a biker.
He suggested (and indicating a company that could do it) to have the parts welded to add material and he would re-machine on top of that.
He talked about a nitrure surface treatment (not sure of english name on that) after machining. Is it a good idea or will this led to fracture points?
He said that the welding company might be able to match the RC of the original part which sounded a good idea.

Do you have (Doug?) the factory dimensions of the parts there. He can measure them with accurate lab style tools but I am a little bit concerned that the condition of my parts may not allow to make accurate measurements or the flywheel might even crawl too much on the shaft.

I will get back to the show tomorrow 11/11 so I can ask him more even though I still can reach him after the show of course...
« Last Edit: 10 Nov 2018 at 19:33 by Eric S »

Offline Doug

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Re: Douglas Aero 1937
« Reply #211 on: 10 Nov 2018 at 22:20 »
Eric,

This is the specifications for the 1930 S6 crank taper, but I believe it is the same for the Aero.



Dimension in inches. On the flywheel side the diameter at the face is 1.160 inch, a little less than the full journal size of the crankshaft.

Not all metals can be nitrided, so some careful attention tot he weld materiel will be required. The tempering temperature for crankshafts was generally around 760C 600C, so nitriding temperatures of 550-575C for gas nitriding should be safe. The rest of the crankshaft will need to be masked to protect it from nitriding and oxidation.

Probably the greatest risk stress cracking is from the welding itself, rather than the nitride hardening. Nitriding is typically a shallow treatment, nor do you require much depth for the flywheel taper. You just need a hard skin to resist fretting and galling. Since the nitriding adds an additional cost, you may want to investigate welding up the taper with a hard facing material and forgo the nitriding. Stellite or manganese steel are two possibilities.

-Doug

[Correction to tempering temperature. 760C used on OHV crankshafts, 600C used on side-vale crankshafts. 11Nov18 -Doug]
« Last Edit: 11 Nov 2018 at 04:20 by Doug »

Offline Doug

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Re: Douglas Aero 1937
« Reply #212 on: 11 Nov 2018 at 04:18 »
Correction: lt looks like some of the side-vale cranks were tempered from 600C. Still above the nitriding temperature.

-Doug

Offline Eric S

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Re: Douglas Aero 1937
« Reply #213 on: 12 Nov 2018 at 15:43 »
While the engine is out of the bike, I will have the dynamo refurbished so it can (maybe) charge the battery.
In 2013, previous owner had an invoice for "BTH M2 CAM RING"
Any idea what this might be.
I have been asked by the re-furbisher if the regulator was inside the dynamo or separate. He needs it so I need to find it but I have no idea what to look for.

Offline Doug

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Re: Douglas Aero 1937
« Reply #214 on: 12 Nov 2018 at 16:27 »
Eric,

"BTH M2 CAM RING" is a ring in the magneto that operates the points.

The dyno does not have a regulator. Trust me, overcharging is not a hazard with the BTH pancake dyno!  :)  There is a BTH cutout that attached to the frame using the nut that holds the post for the hand change lever. This is what the cutout looks like, but the correct bracket is a triangular affair of flat sheet metal.





You can just see the bracket attached to the frame in this picture.



-Doug


Offline Eric S

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Re: Douglas Aero 1937
« Reply #215 on: 12 Nov 2018 at 16:59 »
I do not have a BTH Cut out. There is nothing screwed on the gear level post.
I do have a diode on the wire from Ameter to Dynamo though.
I guess it's doing the same.

Offline Eric S

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Re: Douglas Aero 1937
« Reply #216 on: 13 Nov 2018 at 17:55 »
Doug
Do you have enough head bolts that you may want to sell?

I checked the crankshaft bearings and there is several hard spots I dis not noticed before. I Guess new ones are mandatory. How do we remove them?
I may check that with bearing supplier...

Offline Doug

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Re: Douglas Aero 1937
« Reply #217 on: 13 Nov 2018 at 18:46 »
Eric,

The head bolts that I made are for an earlier model (600EW) and so have a different (and much more ornate) head than what the Aero used. The Aero head bolt looks like this:



A tall hex head, domed, and the thick, plain washer. I don't know that these should be bright; I think originally they were cylinder black. My originals were rusty and quite pitted so I had remade them (many years ago now). I would have to dig the originals out of storage to see if the shanks had any trace of nickel plating on them, but I do not remember such.

The standard practice for getting the crankcase bearings out is to gently heat the surrounding aluminum with a propane torch until just to hot to hold and than thump the crankcase face down on a block of wood so that the inertia of the bearing causes it to drop out of the bore. If it it particularly stuck in place reaching through with a soft drift tapped against the inner race to get it started is o.k. Be sure to work your way around equally so as to not cock and jam the bearing in the bore. Note that hammering on the bearing so that the shock is transmitted through the balls is a definite no-no, but light tapping is probably o.k., and if you are going to replace the bearings anyway it doesn't matter.

-Doug


[fix typo. 31Jul19  -Doug]
« Last Edit: 31 Jul 2019 at 15:28 by Doug »

Offline Eric S

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Re: Douglas Aero 1937
« Reply #218 on: 13 Nov 2018 at 19:50 »
I have well the same screws at least on one 1 cylinder. And they are plated.
Allen screws on other cylinder.
I would like to have same screws on both sides even if not originals...

On a different matter,  how do we handle unleaded gas?

Offline Eric S

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Re: Douglas Aero 1937
« Reply #219 on: 14 Nov 2018 at 07:49 »
What are the tanks capacities?
I will have the tanks treated with a resin and I need to get that information to order the right kit.
The reservoir is well made of steel (not aluminium)?

Offline Doug

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Re: Douglas Aero 1937
« Reply #220 on: 14 Nov 2018 at 13:42 »
Eric,

3.5 gallons fuel and 3 pints oil.

The lack of leaded fuel is generally not a problem unless you run high mileages or run the engine hard for continuous periods such that exhaust valve seat overheats and starts to transfer metal to the valve (valve seat recession). Leaded fuel, introduced in the thirties, helped combat that.

The increasing use of ethanol in fuel is a more significant issue, and you may find you will have to alter the carburetor settings to compensate. There have been quite a few posts on that topic relating to the postwar models.

-Doug

Offline Eric S

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Re: Douglas Aero 1937
« Reply #221 on: 14 Nov 2018 at 14:31 »
Doug

Thank you for the information. I am assuming that is Imperial gallons and pints even if it do not make a huge difference with US standards.
Any idea about the head bolts? Any spare to spare? Anybody knows where we can get them?

Offline Doug

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Re: Douglas Aero 1937
« Reply #222 on: 14 Nov 2018 at 16:25 »
Eric,

The tank capacity came from their catalog information, so would indeed be Imperial units vs. US. When in Rome, as the Romans do...



I did not make any extra of the Aero head bolts at the time (it was 25 years ago),  though these days when I do make something like that I often run off a few extras when I have the machine set up. I do not have any plans to run them again as I have too many other things to machine, but could provide a drawing if you can get them machined locally. Otherwise it would be a matter of advertising here or in the LDMCC magazine.

Unfortunately, and for no good reason I can see, the head bolts are different between the 500/600cc Aero and the 250/350cc Aero.



Both 5/16 diameter, but one a fine thread and the other coarse. Also different lengths, height of dome, and even diameter of the washer. They could well have used the same bolt for all four engines, but did not. Which is a pity as quite a few of the 250/350cc engines have been scrapped looking for crankshafts and conrods that can be altered to keep the 350EW running, so someone might have saved some cylinder bolts and other hardware. However they will not do you any good for a 600.

As you can see, no trace of plating, so original finish would have been black stove enamel.

-Doug



Offline Eric S

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Re: Douglas Aero 1937
« Reply #223 on: 22 Nov 2018 at 07:06 »
Well I found a company that could make the bolts but for just a set they said it would not be effective.
I posted a message in the parts of the forum but nobody interested at this time...
So I will stay with the current set up for now until I found a solution.

Offline Eric S

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Re: Douglas Aero 1937
« Reply #224 on: 28 Nov 2018 at 15:46 »
I removed the valves to paint the cylinder and heads.
I marked them to put them back on their respective port but is it required to rotate them to the same position? (I marked them to do so anyway)
Also do we have to clean them down to bare metal?

Offline douglas1947

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Re: Douglas Aero 1937
« Reply #225 on: 28 Nov 2018 at 16:44 »
Hi Eric,

have you checked the valve seats / valve surfaces?
When you have the valves out, it is a good chance to "fresh up" the seats with regrinding.

Michael

Offline Eric S

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Re: Douglas Aero 1937
« Reply #226 on: 28 Nov 2018 at 18:21 »
No I did not checked but I will have to show them to somebody with more knowledge and probably regrind...

Offline Eric S

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Re: Douglas Aero 1937
« Reply #227 on: 10 Dec 2018 at 19:15 »
I finally had a chance to pay a visit to the company I met at a show last month so they can rebuild the flywheel/crankshaft cone.
We may not go to welding as the flywheel can not be welded all the way in and it would be better to use an intermediate cone. He's thinking right now as to what he can do.

It looks like I will have to have the faces of the valve lifters resurfaced as they are slightly marked. I thought it was fine, he said no.
Also a rubber has been placed behind the bearing on the flywheel side. Is that original?
The bearing is marked SRO. This is a french company that went out of business during the war, so I think the bearing might be original. I will keep it as it's good enough.
The other one will be replaced as it was not quite nice although quite usable.

Sandwiched between the SRO bearing and the rubber I have a thin washer. The mechanic said it was useless and he "would not put it back" as he see no use to this.

Any comment will be appreciated.

Cheers
« Last Edit: 11 Feb 2019 at 15:14 by Eric S »

Offline Doug

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Re: Douglas Aero 1937
« Reply #228 on: 11 Dec 2018 at 06:33 »
Eric,

As mentioned previously, there should be a oil slinger between each end of the crankshaft and the adjacent ball bearing. Not only does this limit the amount of oil blowing through the bearings, it stops any large debris that inadvertently might get loose inside the engine from getting into the bearing. If your mechanic does not recognize an oil slinger and the use thereof, find another mechanic! Between the flywheel side bearing and the crankcase will be any shims required to limit end float of the crankshaft assembly. Even back then 21mm wide double row ball bearings were going out of style, so a 20mm bearing and a 1mm shim was the normal starting point; and then the shims were added to set the end float. I cannot just now remember for certain if there is a felt seal on the drive side; I am reasonably sure it did have one. Often there was on many of the models in this era. If there is a 3/6 to 1/4" deep recess in the crankcase between the bearing and the crankcase wall, then it certainly had a felt. If so, then another oil slinger is required to act as a shield and keep the felt out of the bearing. They were not using rubber rings or seals.

Most late-twenties and thirties Douglas engines that I have taken apart where I felt the bearings might have been original were SKF or Norma-Hoffman brands.

I don't think the face of the tappet adjusters is particularly hard, so resurfacing them and accidentally cutting through the case hardening should not be an issue. The problem with the wear is that you don't know exactly where the valve stem is going to land after a new adjustment. So if it lands half on the original surface and half on a worn pocket, you only have half the full bearing surface. As the valve stem is likely harder than the tappet adjuster, it will rapidly wear into the face of the tappet adjuster until the contact patch approximates the full diameter of the valve stem. Which means the valve clearance will go out of adjustment quicker than it otherwise might have.

-Doug

Offline Eric S

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Re: Douglas Aero 1937
« Reply #229 on: 11 Dec 2018 at 08:33 »
Well I will check with him about the oil slinger; I am surprised as he's definitively involved in motorbike engines and even though a young businessman, he built a lot of motorbike engines, working on hi-performance 2 strokes engines and working earlier for a motorbike restoration company.
The bearing in place now is well a 21mm.

It looks like a least one felt has been replaced with a rubber on this engine... I will check the other end.

Offline Eric S

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Re: Douglas Aero 1937
« Reply #230 on: 11 Feb 2019 at 15:16 »
---

Offline Eric S

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Re: Douglas Aero 1937
« Reply #231 on: 11 Feb 2019 at 15:18 »
I still wiat for the repaired crankshaft to come back...
In the meantime I would like to attend a concern with the kick.
When I use it there is a feeling like if teeths were missed on a pinion.
I see return spring has been changed in 2005 and 2012 and in june of 2012, a hand written note says "Kick Start "POB" and in may of 2012 a Spur Gear Standard Bossed has been invoiced by HPC Gears Limited.
Not sure if those last 2 items are related?
What should I check first. Do I need to open the gear box?


Offline Doug

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Re: Douglas Aero 1937
« Reply #232 on: 11 Feb 2019 at 23:20 »
Eric,

You only need to take the outer cover off the gearbox to examine and work on the kick start mechanism; you do not need to disturb the rest of the gearbox.

Quite possible a tooth has broken.

Douglas always did have a little bit of a problem with kick start mechanisms. The 3- and 4-speeds of the thirties main flaw seems to be a prevalence to jam, particularly when the kick start gear teeth were just starting to engage. They tried to overcome this by using a modified extended addendum tooth form that resulted in the teeth looking rather pointed. Replacing with conventional pinion can cause a problem in miss-matched tooth forms. Same situation as running a 20 degree pressure angle gear with a 14.5 degree pressure angle. Or if both the pinion and quadrant have been replaced with matching standard gear tooth forms, the tops of the teeth can abut when the quadrant starts to engage, which stops the quadrant gear from going into mesh. Hence the pointy teeth; the quadrant is more likely to fall into the tooth space between. Also I think the first tooth on the quadrant may have been eased back and made more 'pointy' so it too would fall into mesh easier.

-Doug

Offline Eric S

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Re: Douglas Aero 1937
« Reply #233 on: 04 Mar 2019 at 11:39 »
The crankshaft has been worked on and the cone rebuilt. However the machinist checked the other end of the shaft and found it was off by 0.2mm on  the end.
Since the bike was running fine until now except for the un-locked crankshaft, is it an acceptable offset or should he make it run straight? (or straighter as he said he had not yet checked if it was S shaped or just bent...)

Offline Doug

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Re: Douglas Aero 1937
« Reply #234 on: 05 Mar 2019 at 04:38 »
Eric,

I know it is a long and limber shaft on the timing side and the bushing in the timing cover will force it true, but the total indicator reading ought to be less than that. A run out of 0.2mm is going to cause undue wear on the bushing. You want to aim for 0.08mm or better.

-Doug

Offline Red

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Re: Douglas Aero 1937
« Reply #235 on: 05 Mar 2019 at 08:48 »
Eric

Do you still have your gearbox apart and if so could you take a photograph of the kick start return spring. I did post a request for help a few weeks back as the new spring I fitted to my Aero did not fully return the kick start lever. I have now established that the new spring I got from club spares is for a 3 speed box and not the 4 speed. Unfortunately they don't hold stcck of any other spring for the Aero and the problem is further complicated by the fact that the club does not have an orginal drawing of the 4 speed spring. Before I or the club get some made I would like to make sure that we know what the correct spring looks like. The broken one I removed from my gearbox again does not appear to be correct and probably why it failed. Photographs of the spring I got from club spares and the broken spring are attached to my original post. Any help will be greatly appreciated.

Roy

Offline Eric S

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Re: Douglas Aero 1937
« Reply #236 on: 05 Mar 2019 at 19:15 »
Gear Box still closed but springs has been replaced at least twice by previous owners over the last couple of decades. But I will let you know and in any case I will post questions and pictures here.
« Last Edit: 06 Mar 2019 at 18:41 by Eric S »

Offline Red

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Re: Douglas Aero 1937
« Reply #237 on: 06 Mar 2019 at 08:28 »
Hi Eric

Maybe your bike has also been fitted with the wrong return spring and this is why it has failed a couple of time. If you can provide a photo at sometime it would be very helpful and hopefully we may eventaully be able to get some correct springs made up. Thanks

Roy

Offline Eric S

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Re: Douglas Aero 1937
« Reply #238 on: 17 Mar 2019 at 14:07 »
Sorry I hadn't yet opened the kick mechanism.
Got the flywheel back from the machine shop.
And of course, waiting for those parts I did not managed to give the tanks a good cleaning and resin treatment and still need to give a coat of paint on the magneto plate.
On this plate we have the oil tap. I removed the screw holding in in place and the mechanism/tap/glass aluminium body do not comes off. Is there any trick there? Any other bolts/screw/nut to remove?
I did not removed and do not plan to remove the oil pump itself.

Also I see on the oil tap a plastic disc numbered 0 to 3 with a needle on top of it that can be rotated like to have an adjustment mark.
I assume the disc must be rotating with 0 matching the ratchet when closed and then the driver can adjust to 1, 2 or 3 with the needle placed to the most common setting for his bike.
I don't remember having seen anything in the manual about that.

There is a bolt holding the tap on the body. Is it just a question of removing the nut to get the tap off?  I assume the tap has a "plug" on the bottom of its shaft. Will it come off the body?
Is there any adjustment on this nut as it looks like if the nut interfere with the tap adjustment.

Offline Doug

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Re: Douglas Aero 1937
« Reply #239 on: 17 Mar 2019 at 15:02 »
Eric,

There are two screws holding the oil sight glass to the corbel on the timing cover. One is the external screw that you readily see. The second is in the bottom of the bowl, where the oil drains out. You have to remove the glass to access it, but if you clean it up a little, you should see two slots for a screwdriver to facilitate removal.

The numbers on top of the oil flow needle do not correlate to any unit of measure. They are just for reference so that you can return the adjustment to any previous value that you found satisfactory. You would set the pointer to the value that gave the optimal oiling rate for normal riding conditions.

-Doug

Offline Eric S

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Re: Douglas Aero 1937
« Reply #240 on: 03 Apr 2019 at 14:42 »
I am preparing the cylinders and heads after having painted them with a special paint for bike's engine.
1. I should have made it before painting but how do you remove the black carbon residu that we have near the valves and in the head?

2. The surface on the head and cylinder gasket plan is not so nice. I don't plan to have them grinded but I would like to have a good cleaning. Is it a good idea to use a piece of glass (supposed to be flat and I have the old sand cabinet window that has been sanded !) and 800 grid abrasive compound?

3. About grinding the valves seats, I have Abrasive compound in 240 and 800. Which one can I use?

4. I know that I have to anneal the brass/copper head gaskets. What is the best way to do it?

5. I guess I have to clean the inside of the cylinders/barrels. Do we have to use this tool below?

Offline Doug

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Re: Douglas Aero 1937
« Reply #241 on: 12 Apr 2019 at 14:36 »
Eric,

There are some carburetor cleaners that will soften carbon deposits but it is probably not worth the risk to the new paint. So typically one manually scrapes the carbon off with a copper or aluminum tool that will not cut into the iron.

A plate of flat glass and abrasive compound is the classic way to lap a surface flat. But it is slow and eventually will wear the glass to a non-flat condition. I use a sheet of wet/dry silicon carbide paper (sandpaper) tapped to a flat surface. This saves wear and tear on the flat surface, and one can start off with coarse grit and rapidly change to finer grit. Nowadays it is easier to find a range of different grit sandpaper in one's workshop supplies than a range of grit compounds. Some light oil or soapy water on the paper will stop it from clogging up too quickly.

Valve lapping. I tend to go with what I have on the shelf in the coarse, medium, and fine grits without looking at the numerical grit value. Some of the tins are so old the labels are not legible anyway!

To anneal copper you heat it to a dull red (in dim light) and either allow it to cool in air, or plunge in a bucket of water. I have seen temperatures quoted of anywhere from 400C to 700C. Quenching in water does have the advantage of cleaning the surface. A little acid in the water will help if the discoloration/scaling is tenacious.

The tool shown is typically what is used here to clean and lightly hone brake cylinder bores. I suppose larger versions can also be used to clean cylinder bores and remove cylinder wall glazing and put in a new cross-hatch pattern to help new piston rings to bed in. But I would not expect that type of hone to do much to resize or true up a bore, nor would I use it to remove a cylinder ridge (the ridge formed where the top piston ring stopped.)

-Doug



Offline Eric S

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Re: Douglas Aero 1937
« Reply #242 on: 13 Apr 2019 at 08:53 »
Thank you Doug

As for the de-glazing of the cylinder's wall, if you don't use a tool, how would you do it?
I am not using any new part (rings or pistons) and I have not seen any cylinder ridge.

Offline Doug

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Re: Douglas Aero 1937
« Reply #243 on: 13 Apr 2019 at 13:59 »
Eric,

Usually for de-glazing you would use an inexpensive tool such as this:



But if you did not want to buy a tool at all, I suppose it could just as well be done with a flexible hand abrasive pad like 3M ScotchBrite or similar nylon matting embedded with silicon carbide grains. Then just get in there with your hand and a helical motion. The cutting action will be so slow that unless you are at it for hours I doubt that you will make any alteration to size or wear any local hollow spots into the cast iron.

-Doug

Offline Eric S

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Re: Douglas Aero 1937
« Reply #244 on: 03 Jun 2019 at 17:00 »
I guess I can say that the re-assembly started, at last.
Lapped and installed the valves.
Any one can confirm the parts are assembled the right way on the valves?
Just noticed that the 2 springs on one cylinder are different than the 2 springs on the other cylinder.
It's barely noticeable on the pictures but the springs are smaller in diameter on 1 half (upper) of their lengths. Any comment?
It's how they were and I put them on the right cylinder. Although I am not sure of the inlet/exhaust position but I lapped them anyway...

Offline Aero

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Re: Douglas Aero 1937
« Reply #245 on: 04 Jun 2019 at 12:48 »
If it helps my springs are all like the one on the right in your pic. As regards the others with smaller diameter at one end personally I'd fit them with the smaller diameter at the top (collett end). Good luck with the rebuild.

Offline Eric S

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Re: Douglas Aero 1937
« Reply #246 on: 29 Jul 2019 at 09:59 »
Well I have not worked too much on the Douglas recently. My lack of engine experience makes feels like I am facing a mountain and I am not sure I can make it to the top.

Anyway, I was having a look at the cover that bear the oil pump and dynamo considering painting it.
However I need to remove the oil drip tapet. There is a large nut in the system, under the glass. However the dripping tube is in the way. This tube moves a little bit but stays in place. Can I pull on it to take it off? Is it just slide in?

Offline Aero

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Re: Douglas Aero 1937
« Reply #247 on: 30 Jul 2019 at 14:19 »
I am not sure if the tube is easily removable, but I did manage to undo that slotted bolt without removing the tube.

If you remove the small bolt at the rear of the oil drip assembly then it is possible to turn the whole assembly anti-clockwise which loosens the slotted bolt & then it can be easily removed with a flat blade screwdriver.

Be careful that you do not lose the tiny spring & ball bearing that resides at the rear of the top assembly, as it will fall out when you turn the assembly.

My spring was broken into 2 pieces, so I wound a new one out of music wire (guitar string!).

Offline Doug

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Re: Douglas Aero 1937
« Reply #248 on: 30 Jul 2019 at 18:23 »
Eric,

I seem to recall the oil bib threads in, but I was able to work around it in-situ with a screw driver to undo the hollow screw in the well of the bowl.

-Doug

Offline Red

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Re: Douglas Aero 1937
« Reply #249 on: 31 Jul 2019 at 14:30 »
On my 600 Aero and my son's 500 Aero the drip tubes are screwed in. I used a pair of thin nose pliers just to gently rotate the tube. Refitting the tube is a bit fiddly or my fingers are too big. I inserted the tube into a bit of thin rubber pipe and was then able to screw the tube back in place giving it a final tighten with the pliers.

Roy