The BSA A7-A10 Forum

Technical => Clutch, Primary, Gearbox => Topic started by: t20racerman on 18.02. 2017 08:24

Title: What is the gearbox lug/clutch cable thread?
Post by: t20racerman on 18.02. 2017 08:24
Hi all

I've had my A10 for 34 years and can't remember when I last changed the clutch cable. It needs replacing now but the threaded adjuster on the gearbox end of the old cable is NOT the same size as the threaded gearbox lug it fits inside. Not that this has ever mattered, as the threaded adjuster fits inside easily and the locknut holds it tight.

I've sent off my old cables to be remade (all non standard) and the guy at JJ Cables who is remaking them wanted to know what the thread size SHOULD be as he may have a correct fitment.  I’ve no idea what the clutch casing lug thread size is though – it looks like British Cycle thread and is about 7.5mm in internal diameter. A 5/16” bolt slides straight in and a 3/8” one is too big. Has the lug been modified, or is my old cable incorrect? It would be nice to know what it should be.
The bike is a bitza - a '59 A10 engine in a '61 A7 chassis.

Thanks

Adrian
Title: Re: What is the gearbox lug/clutch cable thread?
Post by: bsa-bill on 18.02. 2017 09:26
HI t20racerman
The lug on some gearboxes is not threaded at all I believe , one of mine certainly isn't the other I'm in two minds about whether the has been a thread in there or it just looks that way from the adjuster siting in it (same thing as yours I just tighten up the lock ring).
Also one gearbox lug is complete, the other has a cutout for the cable inner to go through.
I wonder though that BSA would use cycle in alloy , a coarser thread would have been better surely.
as always I stand to be corrected (and learn)
Title: Re: What is the gearbox lug/clutch cable thread?
Post by: Greybeard on 18.02. 2017 14:04
On my Plunger the lug is threaded. From memory I'm pretty sure the thread is finer than Whitworth as it functions as a method of fine adjustment for the cable. The cable adjuster ferrule has a locking nut.
Title: Re: What is the gearbox lug/clutch cable thread?
Post by: muskrat on 18.02. 2017 21:05
G'day Adrian.
The lug on the g/box is 1/4" Cycle (26tpi). On later models the thread was eliminated and just a plain 1/4" hole with no adjuster used at the box. Your lug has been modified (read butchered) so the adjuster slides in but the lock nut (ring) can't lock against anything so will lose adjustment over (very short) time.

This just prompted me to change the cable on the 57. Bugga, the inner on the new cable is about 1" short to use the two adjusters or 1/4" short even with the h/bar adjuster removed. Now the tedious job of shortening the outer cable.
Cheers
Title: Re: What is the gearbox lug/clutch cable thread?
Post by: duTch on 18.02. 2017 22:12
 Read this earlier and went to double check, but Musky rounded me up; I'd always thought it was 14 cycle/bsf but thought best check.

 Mine has a spring between the adjuster and clutch arm, which in theory hold the internal adjuster of the pushrod, and also may hold some tension on the cable to stop the adjuster undoing itself  *dunno*

 t20, a while ago I also bought a generic cable for a spare, and it has an adjuster on it that is bigger than 7mm, so probably metric and won't be using that either.

  Thing is I can't find those adjusters in any parts list or diagram, so no part #, all lists just show 'cable complete' or similar. I guess the best shot maybe swapmeets


Title: Re: What is the gearbox lug/clutch cable thread?
Post by: RichardL on 18.02. 2017 22:40
Now the tedious job of shortening the outer cable.

Muskrat,

Just wondering if you do this the same way I do, which is to cut through the outer armor with a fine Dremel cutoff wheel. Doing this, the spirals soon separate and I tweak them off the cable with a couple of pairs of pliers.

Richard L.
Title: Re: What is the gearbox lug/clutch cable thread?
Post by: Greybeard on 18.02. 2017 23:08
... Mine has a spring between the adjuster and clutch arm...
Oh goodey; an even heavier clutch pull  *smile*
Title: Re: What is the gearbox lug/clutch cable thread?
Post by: muskrat on 19.02. 2017 01:29
G'day Richard. Yep that's how I do it. VVVEEERRRYYY carefully, one slip and nick the cable  *pull hair out*. All done, took 1/2 hour!
Cheers
Title: Re: What is the gearbox lug/clutch cable thread?
Post by: duTch on 19.02. 2017 09:49

 
Quote
Oh goodey; an even heavier clutch pull  *smile*

 Well yeah, but not really- it's not a massively heavy spring- quite light actually, and very little preload/compression just enough to do the job.

 
Quote
Muskrat,
Just wondering if you do this the same way I do, which is to cut through the outer armor with a fine Dremel cutoff wheel. Doing this, the spirals soon separate and I tweak them off the cable with a couple of pairs of pliers.
Richard L.

 When I have to do this, I use 'End Cutters'/ fine pincers/ nips (used for tying steel with wire) side cutters will do same, and starting at the point I need to cut and work to the outer cable end, spread the windings apart so the inner can be wound out, and then go to the start point and cut it with the nips at 90º to the cable. Works for me