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Dave

2024-06-11, 20:02:05
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Douglas Aero 1937

Started by Eric S, 21 Dec 2016 at 22:14

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Eric S

I would like to read some advice from the specialists here before I can proceed with laser welding...

cardan

Hi Eric,

Your questions are hard to answer without having the crank on the bench for inspection. That said, the rollers and the sleeves both look marked and worn, which for a roller big end is no good. You can verify this by measuring and close inspection.

The rollers can and should be replaced. If damaged, it might be possible to lightly regrind the outer surface of the of the sleeve on the pin and the inner surface of the conrod bearing (do the rollers run in the rod, or is there a pressed-in sleeve?) and fit oversize rollers, but replacement of the lot would be best.

Getting the correct end float for the big ends is part of the setup, although if the con rods are straight (this needs to be checked carefully) the exact end float is probably not critical.

I'm not sure what that shim is doing. But then, I would have said that the bearing cage could not possibly be original (quite the sparsest set of rollers I've seen in a big end), and the three pins... ghastly. A crank like this would be ok in a bike from the early 1920s, but it looks very out of place in the mid 1930s.

I'm not sure when pressed-up cranks came into common use, but my guess would be that a Velocette of the era would just have the crank pin pressed into the flywheels? Pressing the crank pin onto a shoulder is a solid way of doing things, but there is a problem if - as in the Douglas crank - there is a sleeve over the pin. If the pin has a shoulder, how long should the sleeve be? It is impossible to get both the sleeve and the shoulder to bear equally on the face of the flywheel/crank throw. I've recently done up and engine (a Spacke DeLuxe) with this problem (and more), but it was a 1913 design, not mid 1930s!

Good luck,

Leon

Eric S

Leon
thank you for taking time to reply
I know it's difficult to have opinions based on pictures. Just try to gather informations...

Do I have any chance at all to get new cage bearings anywhere?

Can you explain what the end float is. Is that longitudinal play in the crankshaft?

What do you mean with the sparset set of rollers you've seen?
The 3 pins on both side will be replaced and holes reamed.

The guy I met that'll do the machining worked on a french Terrot from 1910s. He said the crankshaft was built like a modern bike (pressed-up crank?) with a press fit of the shaft's different parts.

The sleeve on the timing side is locked with Loctite and proved difficult to pull. Would you remove it for inspection or leave it here?

Also per my post #449, I see a hole on just one of the 2 pins of the center web. Is that normal? I can't see any (oiling) use for this hole.

Thank you again.

Doug

Eric,

The holes in the crank pin and the web are for the 1935 oil delivery method from the timing side end of the crankshaft. They would not be present on 1936-38 engines.

There are not supposed to be shims alongside the crank pin/conrod. The side or axial clearance Leon refers to is between the sides of the conrod and the crank throws. The width of the conrod big end eye should be about 0.010" narrower than the width between the throws. This is so that as things expand and flex (especially flex!) the conrod does not get nipped on the side. Also while the conrod should be checked to make sure it is straight, the reality is there is always some small amount of imperfection that could cause the conrod to want to take a position minutely off-center. If you try to constrain it, that creates friction and hot spots. 

The rollers in the photos, while not totally trashed, do look like they have had a hard life and need replacement. The crank pin race does not look too well either, but hard to judge from a photo. It might lap in o.k. I would think that the fella doing the laser welding would want the crank pin race removed to get it out of his way, even though it is adjacent rather than under the area he will be working. If the conrod needs lapping, you might need to make a new, oversized crank pin race. You would then also need to bore out the bearing cage as it rides on the crank pin.

Spheric-Trafalger Ltd used to sell bearing rollers in Europe, and I ordered  20k of the 3/16 x 3/16, 1/4 x 1/4, and 10k of the 5/16 x 5/16 while the getting was good twenty years ago. While their metric rollers were made in Europe, the imperial sizes were made in India. Hence ordering a large quantity as you need to sort through with an accurate micrometer and size them in lots by diameter. You do not want to mix diameters greater than 0.0001" deviation. That aside, they did not offer oversized rollers as was once available years ago specifically for the motorcycle trade to enable reconditioning and rebuilding of big end bearings.

-Doug

cardan

Quote from: Eric S on 26 Nov 2022 at 09:34
What do you mean with the sparset set of rollers you've seen?
By sparse I mean the rollers are well spread out. There are 10(?) pairs of rollers in the big end, yet there looks to be room for closer to 20 if the "crowded roller" system were used - usually a cage would have the rollers as close together as possible. More rollers means more contact points means less wear...

Leon

Eric S

Leon
the bearing cages I have are the same Doug showned on the picture on post #191/page 4 here. And they have well 10 windows each, holding a pair of rolls for 20 total per bearing.

The crank pin race (I called sleeve earlier) on the picture is oily and dirty. It is in good condition even if one can see the balls' paths with a different shade on the surface. Surface is smooth and flat.

I was concerned as the bearings assemblies were different. One fell apart and the other one kept the rolls in when removed (probably barely). I thought that one was done and should be replaced as an assembly. Now I understand that we can replace just the rolls. I will check and measure them with a micrometer and/or will source some new replacements.

Doug talked about conrod needing maybe lapping and then a new crank pin race. I did not planned that but will check with the machinist here.


cardan

Yell if you need oversize rollers - I have some; not all sizes but I can look.

Leon

Eric S

I measured the balls with a micrometer (in inches)
I come with a stuborn measure right between .2505" and .2510". Not wandering between those 2, just pointing all the time at the exact same spot, around .2508".
So I would say they have been replaced not so long ago.

From there I will check with my man after laser welding and see if the conrods need any lapping...

Eric S

Waiting for the welding to be done.
I managed to remove this loctited sleeve.
How does it work, is it turning around the stud and the bearing is turning around on the sleeve or is the sleeve somehow locked in place and only the bearing is turning around?

cardan

Hi Eric,

No, the sleeve certainly doesn't rotate on the pin; it has to be fixed in place with the rollers working on the outside. From the look of your photos, the sleeve is designed to be a light interference fit on the pin, and it is sandwiched between the two cheeks of the crank when the hex bolt is done up tight? At least it's easy to remake if worn.

Leon

Eric S

Just got a call form the welder.
The holes that need to be welded (where the 3 pin holes are) are not accessible with the laser machine (or whatever it is) so they will TIG weld it. He's quite conscious of the heat problem so they will use small rods, alternate one part and the other. The stud is short and massive so it should not be a problem and they just need to have very little material added...
Good point is I am saving money.

Eric S

I got the parts back from the welder a few weeks ago and now they are with the machinist. Quite nice chap but overwhelmed with work... Should not be long before he can work on them now.

One point I neglected is the kick. When I was kicking to start the engine (back in the days ...) the kick was slipping so I guess there is a problem with the spring.
My question is (I haven't looked at it lately) how can I access and check this spring?
Is there any care to have when opening the gear box. Is it better to do it on the bench? I assume it would be.

Beside the spring what can be wrong?

Doug

The spring just returns the kick start, Sounds like the helical thread on the Bendix is gummed up. Use a light, non-coagulating oil or a dry graphite lube on helix. Can be accessed by removing the end cover of the gearbox without removing the 'box from the frame, One of the bolts secures the kick start spring, so it is a good idea as you slip the cover off, you jam a bolt (or rod) in the hole to follow up and capture the spring. That way you don't have to worry about unwinding and rewinding the spring.

-Doug

Eric S

#463
Doug
we have the kick that just need to be pulled/extracted.
Then we have 5 bolts about 10-12mm and 1 larger at around 15mm. What this larger bolt holds there?
Is it one of the smaller nuts that hold the spring?
Anyone has a picture of what I may be expecting there?
Will I find gear box oil/grease under the cover or is it dry? Do I need to be ready with a new gasket under the cover?


Doug

Eric,

I do not have the time at the moment to take a gearbox apart and photograph it properly, so will have to make do with what images I already have on the computer.

The area for the kick start gears and spring is separate from the main gear case and is basically dry. There should be some grease on the gear teeth, but otherwise there is no need and some detriment to packing the compartment with grease. There is no need for a gasket.

The fist picture shows the cover removed and the Bendix in place.



Next with the Bendix removed. There is no need to undo the large nut on the outer face of the case. It supports the stub shaft the Bendix operates on.



The kick start spring happens not to be in these particular photos. Also missing is an aluminum hub that slips over the kick start quadrant axle to prevent the inner most coil of the spring from collapsing too much. But the following is a picture of a 1932 type 4-speed with the spring in place. While not exactly the same as the 1934-38 gearboxes, it uses the same idea. The end of the spring loops over one of the cover retaining studs. As you tease the cover off you will see this. Stuff a bolt into the same hole and slide the spring eye off the stud and onto the bolt as you remove the cover. The end of the bolt retaining the spring is indicated by the arrow.



There are some pictures of the other face of the compartment earlier in this topic:
https://www.douglasmotorcycles.net/index.php?topic=6434.msg33372#msg33372
and here:
https://www.douglasmotorcycles.net/index.php?topic=6434.msg33533#msg33533

In the latter the post for the Bendix has been removed, but typically there is no need to do that.

-Doug




Eric S

Thank you Doug but I am not that desperate that I would ask you to open a gearbox for me!

Much usefull as always. Feel more confident now. It definitively helps to see what to expect, can save time later especially for me as if I am a specialist at anything, it's only at making mistakes !

Tazmantic

Quote from: FN on 24 Jan 2021 at 18:08
Doug,
I have redone the tool for removing the ratchet. It is much stiffer and worked well.
Gerd

Sorry to jump
On an old thread but how did you hold the shaft? And how tight was it in the end?

Thanks Neil

Eric S

At last I removed the cover.
I was not expecting grease here as Doug said. Is it possible that this grease migrated from inside the gear box?
I don't see either the "aluminum hub that slips over the kick start quadrant axle to prevent the inner most coil of the spring from collapsing too much". Do I need it?

I can't see anything wrong so I assume the bendix and kickstart quadrant were not timed correctly. It seems the kick was pushing too much the Bendix and was loosing contact.
In the picture I adjusted it so it is on the first teeth. I didn't saw how it was originally as after my first try the Bendix went out.

I can't understand the relation between the bendix and the "crown" on the gear box. There is so much axial displacement of the Bendix, there is probably a very short kick movement after the Bendix engage in this crown!?

So how can I time the 2 gears and is there any other visible problem here?

Eric S

#468
5 days later, it looks like of I have some grease leaking out from inside the gear box. Does that need to be adressed?

I was looking at the way I timed the 2 gears together. I thought it maybe safer to add 1 tooth further in?

Eric S

Re-assembled the gear box cover.
Once the 2 sprockets engages together, the mobile sprockets can't move out any further and then the sprocket/threaded shaft assembly continue to turn (as long as the kick moves) while slipping over the inner shaft so sprocket and kick's gear kind of self adjust. Then the initial position of the gear seems not really important.
Tested by hand (engine removed) and holding the sprocket shaft with a wrench, it seems to give a slipping feeling only when the teeth of the 2 sprockets hits each other "hi-ground" and slip just a little to reach the next tooth.
Can't remember if this was the feeling I had when I was starting the engine...

Eric S

#470
Hello there
I made a mistake and need to have my Douglas aero tank repainted
Chrome is rusted on the rear so may have it completely re-chromed &re-painted
Any Adress in UK or Europe?
I am in France