Centre stand (1965 B40F)

[Phil C]

Please let me know how you get on. I'll be interested to know how much you build up the striking surface by, and also whether you need build up the rear striking surface. Phil

[Spaceman]

I'll post some before and after pics as I progress. In terms of the rear bearing surface on the centre stand, I don't think there will be an issue because the weight of the bike does not come into the wear equation. However, I'll double check the rear stowed clearance when I test fit back on to my B40.

In the meantime, I've ordered a new pair of rear shocks with a length of 11.4". This not because of the centre stand issue as such but is to solve a problem I have with the clearance between the LH pillion foot rest and the brake rod which is marginal due to the longer than OEM rear shocks.

[Spaceman]

Job done. First pic shows one of the pivot holes before repair and the other shows one of the holes after repair. Using my spare C15 frame as a jig, I adjusted the front bearing surface on each leg to give what I judged to be a deployed angle for the stand of about 15 deg from the vertical - previously, it was about 25 deg or so.

When test fitted back on my B40, the difference was very pronounced although the back wheel is probably just touching the ground. However, I've decided that restoring 1/4" extra thickness on the bottom of each foot which is what has worn off over time, which would produce only about 2/3 of this at the back wheel, was not really worth the effort.

Since I've now ordered the correct length of rear shock, this should leave me with the back wheel off the ground by about 1/2" which is probably adequate. In conclusion, I think it was mainly the worn pivot holes that caused my problem with very little repair needed to the bearing surfaces on teh top of each leg.

[Phil C]

Good job, spaceman. I'm not sure I quite follow how the enlarged hole would result in the stand being at the wrong angle. I thought the key issue would have been the striking surface. But anyway, you've obviously sorted it. Thanks for sharing the info and photos.  I plan to get the striking surface at the top of the legs built up by about, say, 1/4" at the front, tapering to virtually nothing at the rear (a length of about 5/8".) But first I'll check that amount by working out the angles, so that I get a pretty  flush strike. I'll probably leave the elongated holes for now and see how I get on.  If you think I'm going down the wrong track, please let me know. Thanks again.      Phil

[Spaceman]

As said, I came to the conclusion that most of the centre stand wear was in the pivot holes - in repairing the holes, I restored the stand deployment angle to what it probably had when it was new. I'm sure you can sort your problem by re-profiling the bearing surfaces on the top of each leg but it will not be easy because the geometry will be a bit intermediate as the pivot point varies when the stand deploys.

I found it quite hard to sort the mechanism even with repaired holes and a C15 clamped upside down in my workshop on which I could test the repairs and make fine adjustments. Without this C15 test jig, I would have struggled to sort the problem. So my advice would be to repair the holes first and then see whether the deployment angle then needs to be changed.

[Phil C]

Getting the holes round again would seem to make sense (as long as the filler material is not too soft and quick to wear.) But I'd be stabbing in the dark a bit as to where the hole centres should be. My inclination would be to follow your suggestion that the correct hole position is at the bottom end of the elongated one. I might just go ahead like that. It's a bit "suck it and see" but there we are. Thanks for help thus far, spaceman.  PS good name, btw.

[Phil C]

Taking a step back, and thinking again about where this discussion started, I think we might have lost sight of the original problem. My issue was how difficult it is to put the bike on its centre stand. That's what started this. The repairs we've been discussing will affect the angle of the stand when it is in use, and are probably worth doing. The stand being at the proper angle might make getting it off the stand easier. But I can't see that they will have any effect on the ease/difficulty with which the bike is put on the stand. It's getting the bike over the stand's vertical point that is hard work. That issue, it seems to me, is determined by the length of the stand's legs in relation to the distance between the stand's pivot point and the ground. I think I have the correct stand, the correct wheels, and the right rear shocks. So whilst making the repairs we've been discussing will hopefully correct the in-use angle of the stand, I'm not sure they will cure the original problem of getting the bike onto the stand, which I'm still none the wiser about. Any thoughts, anyone? Maybe I need to do things like using a block of wood under the back wheel, fitting a lifting handle, etc.   Phil

[JulianS]

My opinion is that the B40 is not that easy to put on the centre stand, it is a poor design.

I think your analysis is about right. Your stand has been mucked about, the legs on your stand have been extended and that means even more effort to put it on the stand and it probably feels like it flops when it goes over the top and back down a bit so to speak. Also probably a bit harder to push it off the stand because it has to go up to get back to the top before it can go down.

[Spaceman]

The difficulty of getting a B40 (or any other motor bike) on to its centre stand will relate to the angle the centre stand makes as it is lowered to the ground prior to pulling the bike on to it. The bigger the angle to the vertical, the more force that will need to be used to pull back on the bike. Also, the bigger the angle, the higher the bike will have to be raised before the centre stand tilts forward to lock into the open position.

At the moment, the angle mine hits the ground just before pulling back on the bike is probably about 15 degrees meaning it is easy to get the bike on to centre stand. However, when I fit the slightly shorter replacement shocks, this angle will increase to about 25 degrees and obviously it will then require more force to pull back on the bike.

In the case of the B40 in question, it would be interesting to know what the angle is as the centre standing is lowered to the ground. Rather than trying to measure it directly, it can be determined from the height of centre stand pivot, H, above the ground with the bike vertical and the centre stand stowed, and the length of the centre stand is L - the angle will just be acos( H / L).

If this angle is 30 degs or less then there's probably not going to be much you can do about it but, if for example it is 45 degs or more, there should be room for improvement.

[Phil C]

Spaceman, where did you position your new holes? At the bottom of the old elongated ones?   Phil

[Spaceman]

Yes at the lower position - it's a bit counter-intuitive but, if you consider what happens when the centre stand deploys, you can see that the grinding action of the pivot pin is upwards.

[Phil C]

I keep thinking of potential problems! When you've bushed the holes, and you come to drill the new ones, you need to get them in line with each other. How did you do that?   Phil

[Spaceman]

I basically assumed the lower part of the elongated holes were accurately drilled by BSA and drilled my holes in the same place. On one side, that worked out ok but, on the other side, I had to adjust its position slightly. In hindsight, the approach I took was a little bit crude from an engineering point of view and I was lucky to get away with it.

If I had to do the repair again, I would try to use a milling machine setup to mill out the holes so that I could position them accurately relative to the bearing surface on the top of each centre stand leg. If you don't, the bearing surfaces will not engage properly with the corresponding flat surfaces between the pairs of frame pivot lugs and the stand angles will be completely wrong.

[Phil C]

I think that to do this job properly would need either equipment I don't have, and/or money I don't want to spend paying someone else to do it. So I think for now I'll just put the stand back on the bike and live with it, and keep an eye out for a good replacement, as Julian suggested.

So you could say I've achieved nothing and wasted everyone's time. I hope you don't feel the latter. But I've gained an understanding of how the thing works, and it's foibles, and it's been interesting.

When I've reassembled the centre stand, I'll turn to the side stand which, Adrian said recently, needs attention. I'm not sure yet what's wrong with it, or how to remedy it, but I'm guessing maybe the bike is leaning over too far. I'll send some photos, and ask some dumb questions, when I come to looking at it.

Thanks again everyone for your advice.

Phil

[Spaceman]

I wasn't happy with the way I repaired my centre stand, for various reasons, and am going to try a different technique with the spare C15 stand I have. Basically, I'm going to try to fill the unwanted part of the elongated hole with weld material rather than welding in a piece of filler metal - success will depend on whether my limited welding skills are up to the job! If the new approach proves to be practical, I would be happy to have a go at repairing your centre stand if you are prepared to take the risk?

In terms of the sidestand, the one on my B40 is pretty useless because it is at the wrong angle and, like yours, it leans the bike over too far. I'll have a close look at it later to see whether I can determine what is causing the problem. Unfortunately, short of heating up the mounting lug to 825 C to melt the braze material to allow the lug to be rotated on the frame, I suspect it will not be an easy problem to sort out.