Author Topic: Centre stand (1965 B40F)  (Read 943 times)

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spaceman

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Re: Centre stand (1965 B40F)
« Reply #30 on: 25 April, 2022, 19:48:07 »
When you say the uppermost part of the hole is okay, do you mean the bit nearest the vee, or the bit that is uppermost when the stand is folded up?  Phil
With the stand vertical, I think most of the force on the pivot holes will have been downwards which will be the direction of maximum wear - the bit of the hole near the V-shaped top to each leg will therefore be relatively unworn and should define where the hole started life.

I don't think there will be any problems with the strength of a repair involving brazing in a bush to restore the pivot holes. However, as an exercise, I am going to carry out the repair on my surplus C15 stand by welding although I may have to find a milling bit to restore the hole afterwards?

In terms of finding a replacement centre stand, I suspect that we are seeing typical wear for a 57 year old motorcycle and you may find it hard to find one in better condition?

Phil C

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Re: Centre stand (1965 B40F)
« Reply #31 on: 25 April, 2022, 20:57:32 »
Decisions, decisions...

I guess it could take years to find a good one? (Good excuse for going to lots of jumbles though! But then there aren't many near me in SWDevon) There wouldn't be any NOS ones, would there?

If the hole wear is at the top end (spaceman seems pretty confident it is) then the bush, which would of course have an off-centre hole, would at the top be, say, 2mm wall thickness, and the parent metal (ie the leg) would have, say, 3mm wall thickness. Or vice-versa, or something very roughly like that. Both the bush and the hole it fits in would need a sizeable chamfer to hold braze, as the braze couldn't be proud (it would have to be dressed back flush) or the thing wouldn't fit in between the frame lugs (I think.) So there would be thin walls, with a chamfer taken out as well. Not much material left then, is there?

I'll be extremely interested to see how spaceman gets on with his surplus C15 stand. Very, very kind of you, spaceman.

Thanks again all. Interesting, isn't it? (mental note: must get a life!)              Phil

Phil C

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Re: Centre stand (1965 B40F)
« Reply #32 on: 26 April, 2022, 06:31:17 »
A thought I've had is that I could leave the hole as it is, and just get the stop surface built up with weld.

But Rupert Ratio (vol 2, p 102-3) talks of refurbishing by repairing the holes, and welding on pads under the feet, but I don't think says anything about building up the stop surface.

Another thought I've had is: I believe the stand is made of malleable cast iron? Would welding compromise it's strength by creating brittleness/cracking? Hmmm... it's beginning to feel a little bit like a can of worms.

Phil
« Last Edit: 26 April, 2022, 06:46:39 by Phil C »

spaceman

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Re: Centre stand (1965 B40F)
« Reply #33 on: 26 April, 2022, 07:46:22 »
The centre stand is made of steel as far I can see - there's no reason to make it from cast iron!

I think RR is assuming the only wear is to the pivot holes and the bottom of the feet. From what I can see for the C15 stand that I've got, the top surface is badly distorted from years of hammering as the stand snaps open giving the wrong deployed angle. At a guess, I think the front edge of the bearing surface on the top of each stand legs needs about 1/4" of metal added.

In principle, the pivot holes do not need to be repaired. All that matters is the angle the stand makes with the frame when it deployed and therefore re-profiling the bearing surface to give the correct angle should be sufficient.

JulianS

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Re: Centre stand (1965 B40F)
« Reply #34 on: 26 April, 2022, 08:46:18 »
Go back to my earlier post - the legs are EN8 steel stampings. Google will tell you its properties.

Here is the page from the build specifications.


Phil C

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Re: Centre stand (1965 B40F)
« Reply #35 on: 26 April, 2022, 10:05:20 »
Thanks Julian. I was going by Rupert Ratio. As I understand it, EN8, back in the day, had quite a bit of carbon in it, and there would be a risk of cracking from welding, but that problem might be solved by preheating. Could be wrong of course. Thanks again. 

spaceman

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Re: Centre stand (1965 B40F)
« Reply #36 on: 26 April, 2022, 11:54:16 »
Rather than repairing a C15 centre stand that I have no use for, I thought I would take a closer look at my B40 centre stand which is a bit marginal in terms of supporting the bike. As expected, it shows quite a bit of wear. The pivot holes exhibit the same level of wear as my C15 centre stand - the centre of the holes have moved downwards by, perhaps, 1/4". The forward ramps at the top of each stand leg which determine the deployed angle of the stand have also been hammered out of shape. Finally, each foot has probably been worn away by at least 1/4".

I'm going to repair the pivot holes first. Once done, I will re-profile the forward ramps on each leg to give me a deployed angle of, say, 15 deg to the vertical - at the moment it is probably about 30 deg. Once these two repairs have been done, I'll then see how much the centre stand feet need to be increased in depth to give me a back wheel 1/2" - 1" off the ground.

In terms of EN8, there's going to be no risk of problems during welding - it's just a slightly higher carbon content mild steel!

Phil C

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Re: Centre stand (1965 B40F)
« Reply #37 on: 26 April, 2022, 12:24:54 »
I'll be very interested in how it goes, spaceman. I take it you have equipment such as welding gear, lathe, maybe be even a milling machine or maybe a pillar drill? Do you plan to weld the bush in place, or braze it? I guess you'll be welding it in, otherwise the welding heat to build up the stop surface would probably melt the braze. I was reading online that EN8 used to have more carbon in it (medium carbon steel) than it does now (unless I misunderstood.) Anyway, please let me know how you get on. Hope it goes well. New pins just arrived in the post here.  Phil

spaceman

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Re: Centre stand (1965 B40F)
« Reply #38 on: 26 April, 2022, 13:45:02 »
If I had an oxy-acetylene torch, I would do a braze repair which, unfortunately, requires the metal to be heated to about 825 deg C! What I'm minded to do at the moment is to fabricate a piece of metal shaped to completely fill each distorted pivot hole and to tack weld them in place. Having done this I can then more easily drill out the hole before completing the welding of what's left of the added metal.

Interestingly, having messed around with fitting my B40 centre stand to the C15 frame I've got, I think I've come to the conclusion that the pivot holes have actually been worn upwards rather than downwards rather counter-intuitively! I will certainly need to double check this before I drill the new holes! 

Phil C

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Re: Centre stand (1965 B40F)
« Reply #39 on: 26 April, 2022, 15:54:16 »
The bearing surface on the frame appears to me to be about 15 degrees to the horizontal (sloping down towards the front.) I guess ideally the striking surface on the top of the leg should hit it flush along its striking length, which appears to be roughly 5/8". So, on mine anyway, the front edge of the leg's striking surface needs to be built up a lot more than the back. I'm guessing around 1/4" more than the back  (but a bit of geometry/ trig would work it out more accurately!) Photo shows one of the worn legs.  Phil
« Last Edit: 26 April, 2022, 16:04:24 by Phil C »

spaceman

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Re: Centre stand (1965 B40F)
« Reply #40 on: 26 April, 2022, 16:38:56 »
That sounds about right to me! I will be working out the overall geometry for my B40 so that I can relate the angle of the centre stand and its length to the height the back wheel lifts off the ground. One thing I need to check is that my rear shocks are of standard length??

Phil C

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Re: Centre stand (1965 B40F)
« Reply #41 on: 26 April, 2022, 18:11:37 »
I'm afraid I don't know what the standard length for the rear shocks is. Here's a photo of mine.

spaceman

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Re: Centre stand (1965 B40F)
« Reply #42 on: 26 April, 2022, 19:57:15 »
Here's the thing - standard length according to RR is 11.3" but mine is 11.9" which seems to be what is now available on the market. Unfortunately, this means the centre stand now needs to lift the bike an extra 0.3" (to give 0.6" at the rear wheel) compared with when the bike was new. Not a lot but needs to be taken into account, at least for my B40!

Phil C

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Re: Centre stand (1965 B40F)
« Reply #43 on: 26 April, 2022, 20:30:48 »
Hmmm... bit of a devil.

How's the hole repair going?

Phil

spaceman

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Re: Centre stand (1965 B40F)
« Reply #44 on: 27 April, 2022, 06:47:34 »
I should have it done this morning. Actually looking easier than I thought because I will be able to use some steel rod as the filler material rather than having to laboriously cut out and shape some sheet material. Once tack welded in, I will use my pillar drill to drill out the new pivot holes which, hopefully, should be straightforward.

What I will then need to do is work out what is the steepest angle I can get away with for the centre stand. A quick measurement shows it is currently at about 27 deg from the vertical and I intend to see whether 15 deg would be ok. However, this difference only amounts to about 0.6" in terms of the change in centre stand pivot height above the ground which probably only amounts to about 0.4" at the back wheel. If this is verified when I put the stand back on the B40, I'm going to have to gain any further height by increasing the thickness of the feet?

As said, part of the problem I have to face is that the 11.9" rear shocks I bought many years ago for my B40 are too long and should have been nearer 11.3". So it may turn out that the best I can do with my centre stand mods, is to end up with the back wheel just clear of the ground rather than the 1/2"-1" I would have hoped for.