Shortening inner throttle cable

[BSA Bob]

I wanted to shorten an inner throttle cable for my R26 to give a straighter pull at the twistgrip throttle chain.
Currently the adjuster at the carburettor has to be screwed out to its extremity to properly adjust the cable.
Practicing on an old cable, I used a gas torch & even with everything red hot I wasn't able to move the small nipple. Does anyone know why this would be?

[BSA Bob]

[Einzylindär]

Hi Bob,

modern throttle cables seem to have nipples casted around the inner steel wire.
As they are grey matt they are not made from brass.

best regards
Stefan, the one cylindrist

[strichzwojan]

Might it be you have a pressed nipple and not a solderd one...

[cwf]

As they say, it sounds like the nipple is crimped/squashed/compressed to the cable. Long ago, they were soft-soldered. If you have a brass nipple with a counter-sunk hole, cut the cable to length and slide the nipple on. The final 1/8th inch or 2mm of wire then needs to be squashed open, so as to fill the counter-sink. Tin the end, ie pre-solder. Slide the nipple to the end and heat it so that it is joined to the wire.

All easier said than done and practice makes one better. The problems I used to have were getting the wire to accept the solder, either because the soldering iron wasn't hot enough or the wire wasn't clean enough and squashing the end of the wire the right amount. Soft solder on its own is not enough to hold a brake wire safely.

[Stefan]

Bob, What if you lengthen the cable hose instead of shortening the inner cable. Use a cable adjuster screw, cut it to the desired length and remove the thread so that it fits into the adjuster screw of the carb (or the throttle grip's). Works without disassembling the cable.

[BSA Bob]

Thanks for these replies. Yes, the nipple is certainly crimped on in some way because heating makes no difference.
I tried trimming the inner cable & soldering on a nipple but the solder didn't take. Perhaps due to oil in the cable that I couldn't clean out?
But fortunately I found a longer cable adjuster, I think from a later (6 series?) boxer. It has 12mm thread length as opposed to the 7mm length of what I originally had. It now fits very well.
The carb is for an R27 (forgotten which one) which has been "backdated" to resemble an R26 type. It now has the top with the curved tube, & the adjuster is very hard to get at. The R27 type with the vertical adjuster is much easier to work with.

[4Taktix]

G'morning Bob,
hope you only did your soldering practice on an old cable.
By heating up a cable red hot, you create a predetermined breaking point!
(steel loses its hardness/tension)

[Borgward]

Crimped nipple and soldering problems: you probably got a stainless steel cable
Hubi

[BSA Bob]

Yes, I did practice on an old cable, 30-40 years old at least, just stuff that never got thrown out. But looking at these old cables, they're a bit scruffy but OK.
I hadn't thought about stainless cables. I'll try a magnet on them & report.

[4Taktix]

Either way you need an appropriate flux-agent. ( based on phosphoric acid for stainless steel )
thoroughly degreasing is also mandatory. Relatively low temperatures and a capable soldering iron.
Finally the remains of the flux (very aggressive) have to be cleaned/rinsed off neatly.
There's also all required hardware on the web to DIY your own cables.
For throttle there were some with only the tiny little nipple for the carb slide on one end, other end free,
length to chose on order. For the Throttle-twistgrip there were several to choose from, but even the small were
available with a grub-screw, so you woun't have to solder.
For Throttle there were no significant forces to expect, so no problem.
Brakes were a different story. 

[BSA Bob]

The cable I tried is steel so I can only think I wasn't able to clean it enough. I make other cables for my BSA using appropriate nipples but I've never had to make one with the small nipples used for the BMW throttle.
One thing I noticed was that the several old cables lying around all had the same comparative lengths between inner & outer. Using these on my R26 means there's a massive amount of slack in the cable before the slide starts to lift. On a 250 where you're usually using a lot of throttle this means a hell of a lot of rotational twisting when changing gears.