Author Topic: Douglas Aero 1937  (Read 118225 times)

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Offline Eric S

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Re: Douglas Aero 1937
« Reply #450 on: 24 Nov 2022 at 15:25 »
I would like to read some advice from the specialists here before I can proceed with laser welding...

Offline cardan

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Re: Douglas Aero 1937
« Reply #451 on: 25 Nov 2022 at 00:40 »
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

Offline Eric S

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Re: Douglas Aero 1937
« Reply #452 on: 26 Nov 2022 at 09:34 »
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.

Offline Doug

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Re: Douglas Aero 1937
« Reply #453 on: 26 Nov 2022 at 14:59 »
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

Offline cardan

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Re: Douglas Aero 1937
« Reply #454 on: 27 Nov 2022 at 04:31 »
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

Offline Eric S

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Re: Douglas Aero 1937
« Reply #455 on: 29 Nov 2022 at 09:32 »
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.


Offline cardan

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Re: Douglas Aero 1937
« Reply #456 on: 29 Nov 2022 at 11:04 »
Yell if you need oversize rollers - I have some; not all sizes but I can look.

Leon

Offline Eric S

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Re: Douglas Aero 1937
« Reply #457 on: 29 Nov 2022 at 19:23 »
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...

 

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