C15 Forks

[Morleydog]

Ok so the next issue I am having with the forks / steering on my C15. The 2 pinch bolts that go through the bottom yoke do not seem to tighten on to anything. The fork leg goes through but has clearance even when they are fully tightened. It seems like there should be a bush or something in there to take up the slack, but drawings don't seem to show anything either. Any ideas what is wrong?

[chaz]

are they the original stanchions or replacements?

[Morleydog]

Hi Chaz. Im really not sure to be honest. I asume the diameter of the stanchion is correct, because I bought some new seals and they were a nice fit over the forks.

[idie]

Just a thought, are the C15 stanchions the same diameter as the A10 if they are narrower then may be the bottom yoke is off an  A or B model.

[chaz]

reason I asked is that the T100 uses T140 forks with TLS brake, the B40 uses A10 stanchions with spacers made up due to the double cost of B40 ones, the seal diameters may be the same standard size but the yoke diameters could be  different. If they have always been together then has the yoke been heated up in repainting?

[Morleydog]

Couple of good points there. I have only had the bike 6 months and most of it has been in pieces. However, I did ride it for around 20 miles before I started dismantling. I need to pull it back apart and measure the difference. I had the yoke powder coated so not sure about the heat, but I think the difference is too much. I may be able to get a bush made up with a saw cut so it clamps onto the stanchion.
Thanks for your help.

[Morleydog]

OK, so finally stripped it back down. The fork stanchion (the part at the top which is turned slightly smaller than the rest) measures 31.2mm. The bore in the bottom yoke measures roughly 34.2mm (this may be slightly smaller than when manufactured due to trying to pinch it right up).
Could anybody tell me which of these is correct?
Also, is the answer, to make a bush with a saw cut down the length, to take up the slack. Once it is all clamped up it should be ok....I think?

[Blackthou]

Have you tried tightening the pinch bolt with the stanchion to check what it will close down to? It may be a very thin walled bush or even a roll of shim. Sounds like one or the other isn't right unless the bolt is knackered and it would close down, hence the question.

[Morleydog]

Good point, I will go try now. However, thinking about it, there is a gap of only 2mm - 3mm for the pinch bolt to tighten. 3mm off the circumfrence would be 1mm off the diameter, when I am looking for 3mm.
I will go check. Thank you.

[Morleydog]

I;m afraid, having measured, the gap in the yoke split is actually nearer 1mm so no chance of closing onto the stanchion.
The wall thickness of any bush / shim would need to be around 1.5mm so not sure if it is possible to turn that thin but I will enquire.

[Blackthou]

Well done for checking, a 1.5mm wall would be difficult but not impossible to make hence my suggestion re shim strip. You may find someone makes a plain bush that size in a bearing catalogue. Once either is clamped, they won't go anywhere.

Any thoughts as to which of the yokes or the stanchions isn't the correct size? I'd hope it was not the stanchions but the yokes otherwise they may prove a week point. Bit of a puzzle all round.

Good luck

[Morleydog]

I am guessing the bottom yoke is the imposter, but I cant be certain.
As I have previously said, I bought new seals which seemed to be a good fit on the stanchions.

Is anyone able to give me the correct dimension for the outside diameter of the C15 stanchions (1960)?

Thanks again!

[Blackthou]

Mine's 1960/61. Iirc the stanchion is a bit of a pain to expose. I may be able to check for you Saturday. Where abouts and what dimensions do you need measuring?

[Morleydog]

The plot thickens. There is what appears to be a part number on the bottom yoke. Only trouble is, the p[owder coat means it is not 100% readable. See attached picture. It appears to be 40-5096. I believe the corract part number should be 40-5041. I have trawled through most other marques looking for this or similar number but to no avail.
This seems to support the idea that the bottom yoke is the incorrect part.....or does it.

Blackthou, please don't go to too much trouble to measure the stanchion. I presume you have the fork trouser like mine. If you cannot access, don't worry. I have already made enquiries about bushes.

[chaz]

https://www.ebay.co.uk/itm/BSA-B25-250-Triple-Tree-Bottom-Yoke-40-5096-/321428934213