Sturmey KB 3

[peetee]

I have a Sturmey KB 3 hub with a missing actuation rod/chain. It appears from this reference http://www.sturmey-archerheritage.com/i ... c-26.1.jpg that the rod (N7) has an internal thread at the hub end quite unlike the external thread on the majority of Sturmey hubs. Granted, it's a poor drawing so possibly not accurate but I have tried a particularly long 'conventional' actuation rod that goes in, stops but doesn't thread. Can anyone confirm this internal thread and comment as to a source for such a part?

[Brucey]

IIRC there is a devious arrangement of springs inside the axle which is quite unlike the arrangement on other SA hubs. IIRC one spring is the main shift spring that you feel resisting the movement of the shifter (this spring bears against the hollow grub screw in the RH end of the axle) , and the other is a 'shift control spring' which allows the shifter and control rod to move on a downshift even if the clutch in the hub is not yet ready to follow suit. The two halves of the control rod screw into one another and the main (RH) shift spring bears against a tiny brass collar that is trapped between the two halves of the rod. The key is plain drilled and is sprung rightwards against the collar by the LH (shift control) spring.

If these parts are not all present and correct then I suspect that you are onto a sticky wicket. It may be possible to create something to replace the two halves of the control rod and one of the springs using FG/FW parts but I'm not sure about this; anyway there would have to be modifications for sure. Another possibility is to use a control rod from a 'sprinter' 5s, together with a special toggle key, and to lose the shift control feature altogether.

As it happens I have a working KB3 and if you are really stuck I can dismantle and photograph the bits for you.

cheers

[Brucey]

BTW I meant to say, I would have suggested 'oldbiketrader' as a source of spare parts but as I understand it he is no longer trading.

The K series design is about a hundred years old now. It was a different world then

https://www.itsnicethat.com/system/files/032013/5139b7c65c3e3c7dad000568/images_slice_large/1919-the-old-timers-advertisement.jpg?1438271033

cheers

[peetee]

Thank you Brucey that's a very generous offer and I will take you up on that. I am not yet familiar with the workings of these hubs having for years handed any problems over to a very keen mate who's eyes all but illuminate at the mention of Sturmey. A mixture of laziness on my part and not wishing to disappoint a pal. It would be a bit like taking him to a real ale pub and sitting him in front of a glass of water. Sorry. I am digressing like Ronnie Corbett now.

[Brucey]

pending photos, there is a better diagram of the control rod parts here

https://hadland.files.wordpress.com/2012/07/type-kb-1937.pdf

cheers

[Brucey]

this is the control rod from what I think is the final version of the NIG KB hub, which has AW-type high gear pawl springs.

approximate measurements in mm, all as per fitment to a ~153mm axle.

the toggle chain emerges from the RH side of the hub. The disassembly procedure is

1. the LH pushrod can be pushed well into the hub and held using a screwdriver and
2. the RH part of the control rod (with the chain) can be unscrewed and removed
3. Let the gear definitely shift into top and then the long left part of the control rod can then be withdrawn together with the shift control spring
4. The grub screw in the RH end of the axle can be unscrewed and
5. The main shift spring (which has a small brass collar set in the end that bears against the toggle key, and looks a bit like an FW/FG shift control spring) can then be removed.

The toggle key stays in the hub, unless there is further disassembly. Before reassembly (which is more or less the reverse of the above), make sure that the hole in the toggle key is still presented to the control rod correctly.

BTW it seems tempting to unscrew the LH rod using a screwdriver; this would be a bad idea, since it tends to cause the shift control spring to snag and deform. Unscrewing the other end is a much better idea, I think.

The correct adjustment with these parts is to have the rod flush with the LH end of the axle in gear 2. There is no useful indication on the RH end, and indeed the plain part of the rod never emerges from the RH end of the axle.

cheers

[peetee]

Thank you sir.

[Brucey]

no problem. I suspect that a suitable alternative could be made by using

- FW/FG springs (which might have to be stretched) as substitutes for the K ones where necessary

- a 'sprinter' or (W) 5s control rod

- a specially made LH end to the control rod, which is tapped with the correct thread to engage with the 5s control rod

- a new toggle key by machining one from an AW to fit, or perhaps taken from an FW/FG axle.

I can also think of arrangements that use a length of 14G spoke as the main part of the control rod, and steel spoke nipples welded to the other bits to receive them.

A complication is that the preload on the shift control spring (LH one) has always to exceed the force supplied by the main shift spring (RH one held captive in the axle). I daresay it would be possible to live without the former spring at all; the AW doesn't have it, and the downshifts are only occasionally baulky as a result.

cheers

[Ugly]

You could try: Vince Warner
Colwood Wheel Works
http://www.colwoodwheelworks.co.uk

I've not used his service but highly recommended by fellow V-CC members