Throttle cable snaps, why?

[Riejufixing]

Any experience of this/ides about it?

The throttle cable snaps inside the twistgrip, immediately below the nipple (3) which locates in the plastic rotating part of the mechanism (2), the cable tunning in a deep groove that runs around much of the periphery of the rotating part.

It seems that the cable inner is somehow bent backwards and forwards and breaks at a kink made in it by the "closed" non-grooved part of the rotating mechanism (1). There are some marks inside the throttle housing (the part that the rotating mechanism rotates in) as if the cable inner is popping up out of its groove.

The nipplele should not rotate at all inside its receptacle, the throttle should come up against a rotational stop before all the cable unwinds from the slot.

Two cables broken this way; 1 OE, 1 made up with brass nipples and original 7 x 7 cable (lasted a month).

[Nobby the Bastard]

There's no reason why the nipple should move. Make sure it's in the correct position (so that at rest the cable goes directly down its guide with no bends).

Is the throttle badly adjusted? If it is, when you shut it off you may be accidentally forcing the nipple to rotate.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[RhynoCZ]

Try using some grease. The standard throttle assembly should not require any lubricating, but I'd do it just to see if it helps. I had to lubricate one of those chinese ''quick action'' short ''MX/Enduro'' throttles that I've put on the MZ, as the cable was very noticeably rubbing against the pulley inside the throttle assembly, the rubbing was audible. The whole thing is sealed so I smeared some vaseline (grease) there and it's been like this for maybe 5 years with many, many flat out miles (flat out = 62mph).
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[WD Forte]

what cheap ass shit fucking bike?

I'll have a wild guess anyway
The cable hasn't been set up properly or the inner is too long and gets distorted 'worked' just after the 'nippele' when the throttle is closed and it dont like it, so eventually snaps out of spite.
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bikers smell of wee

[jaffa90]

Stronger return spring. Also all nipples should be able to rotate.

[Sister Sledge]

[colink98]

props for the very clear and informative hand written diagram.
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PCX125 (stolen) - CBF600 (current)
Ride it like you stole it.
ride sensible and not like an idiot and you wont get 6 points in one week.

[stinkwheel]

The heat from the soldering heat hardens the steel cable making it brittle. Solder wicking down the cable creates a stress riser directly below where the solder comes to.

Sometimes an aggressive flux which hasn't been neutralised will also cause corrosion.

If a cable is going to break, that is where it will break.

I bet if you look closely, the cable sticking out of the nipple will be soldered down to where it broke.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[vitus detritus]

Who said the nipples shouldn't rotate ? They damn well have to rotate ! Take some fine emery paper to your nipples and smooth out all the flash (mould lines) and then apply a dollop of grease when you install. And while you're at it, get as much grease/oil inside the cable housing as you can.
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if it ain't broke, don't fix it

[Riejufixing]

[Riejufixing]

[Riejufixing]

So. I made another cable inner up. This is made of bicycle gear change cable, which is not as flexible as 7 x 7, but isn't strained on bends.

The return spring at the carb end (on the butterfly valve) seems OK. Operating the valve manually doesn't show up any roughness.

The cable has been adjusted so that at maximum throttle opening (at the twistgrip) the butterfly valve is very close to fully open. There are a couple of mm "slack" at closed throttle. I have no idea what manufacturer's recommendations are as the manual for this RS3 is not available (GRR!).

It seems to work OK. Opening and closing the throttle a number of times and examining the cable shows no bending, but it did not last time either...

Will keep an eye on it and look for incipient cable damage in a couple of days.

[Sister Sledge]

As stinkwheel says - heat? How much heat are you using? What are you using as a solder to fix the nipple on?
I ask because that's a type of high tensile wire and heat alters the properties of it - it could well be making the wire brittle or perhaps turning it 'soft'.
It's a fine line between those phases of alteration and something you might not be noticing due to the wire being thin and rapidly cooling between heating stages.
Have a story:
I was a blacksmith/welder at a mine. One of our tasks was replacing massive white metal nipples on the end of the steel ropes which raised and lowered the cage in the shafts. Most was straight forward but the heating had to be even (to ensure the white metal adhered to all of the rope strands) but also done through stages. Back then we used something resembling wax crayons which melted at certain temperatures. We'd touch the rope and follow the heat path to make sure we never went too hot otherwise the rope would change in its properties.
Obviously that's not possible given how small your nipples are (ooerr mister) but you get the idea as to how bad too much heat can be.
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CCM 404 DS

[Riejufixing]

[Riejufixing]

[Sister Sledge]

[Triton Thrasher]

That wouldn’t break when he works the twistgrip.
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Rrrrrrrrrrrrrrrrrr

[stinkwheel]