Build - Throttle Cable length and adjustment

[CtrMint]

Evening All,

Today is going a little better with lots of finishing touches being added to the engine bay.  I've got to the point of adding the throttle cable.   As expected in lots of documentation it seems very long for the application.  I understand the recommendation in the manual is to bend the throttle pedal.   However I've seen alternative approaches where the end is trimmed and a cable stops fitted.

I wonder if members would give me their opinion on the best approach.

Thanks

[Jim 123]

The convention is to bend the throttle pedal arm.  Alternative is the thread the cable through the hole in the arm and fit a Kart throttle cable clamp without bending.

https://www.ebay.co.uk/itm/Kart-Cable-Clamps-GOLD-Annodised-for-Throttle-Brake-Cable-Pack-of-4-KPUK/382209600217?hash=item58fd77aad9:g:~AkAAOxywh1TAFrh:rk:3:pf:0

 

[CtrMint]

Thanks Jim,  I thought about it a bit longer and went with the bend approach.  Logic being less potential for cable slippage and an issue when you don't need it, i.e. miles from home and no tools.

I've now bent the pedal and its worked out fine. 

[Petethediesel]

Just think, If they changed the design of the lever, you wouldn't have to do that. Just saying.

[CtrMint]

I did wonder how it would affect the linearity of the throttle, I made sure I got a screwdriver down to the joint to ensure I eliminated any curve at the top.  

[aerobod - near CYYC]

I would adjust the cable at the throttle body to give 1 or 2mm of slack when the throttle is closed, as the cable will tighten a little when the engine compartment is hot and idle will increase if it pulls the throttle off the stop.

[CtrMint]

I've not worked out how to adjust the throttle body side, I can see the threaded section, but it seems to stiff to turn.  I guess I pull the clip out and rotate.  But also won't that increase the slack where it hooks in?

[aerobod - near CYYC]

Yes, pull the clip out then rotate to lengthen or shorten the outer part of the cable. It will increase the slack, but you need just a slight amount to prevent the inner being too tight at idle for all temperature conditions under the bonnet. May require a bit of tweaking once the car is running.

[Bricol]

I'm going to need that one explaining - something tightening as it gets warmer . . . and expands . . . ;-)

Double check the operation/relationship of the pedal, cable, attachment into the pedal box - if the cable is being dragged over an edge as the pedal moves, or forced to bend at the attachment to the pedal, its not going to last long.  Nice smooth arc of operation, no forced bends is the way to go.

I'm still on the original, no wear visible, cable after 17 yrs of pretty continuous use.

[aerobod - near CYYC]

The explaining - differential expansion of materials - various materials in the path where the cable runs and is clamped (plastic plenum, aluminium throttle body, steel cable, spiral steel outer cable with polymer coating). It may not be the same on all cars due to variation in config, but on my R400D the material differential expansion causes the inner throttle cable to tighten relative to the outer, when the engine bay temp goes from 15°C to 50°C or more.

[Bricol]

That's normally the beauty of a bowden cable - that sort of thing pretty much self-compensates out if it's fastened sensibly. The inner would tend to lengthen - assuming your temp rise, by 0.000455 x the original length rather than shorten.  I certainly don't tend to consider it in normal design job until much higher temps.

But no matter - some slack is good - allows the throttle to sit on the mechanical stop rather than rely on the cable, which is probably why I've never found it a problem.

And good smooth arcs of operation as mentioned.

[aerobod - near CYYC]

I haven't looked at the Bowden cable liner on my throttle cable, but the coefficient of linear thermal expansion of a PTFE liner would be 0.000125 per degree C (inside a spiral wound steel outer which would provide little resistance to it's expansion, compared with 0.000012 for the steel inner cable. Any plastic liner will have a linear thermal expansion coefficient in the range of 100 x 10^-6 m/m/K, approximately 8 times that of steel.