Throttle Cable

[FlyingMonkey]

In the process of doing other maintenance, I discovered the throttle cable on the right carb is a bit frayed where it connects to the throttle arm.  Can this be adjusted at the throttle end by feeding more cable through to a non-frayed grip area, or do I need to replace?

If I need a replacement, can somebody point me to a source?  The Parts Manual lists this as “1mm 7x7 steel rope”.  I’m sure it’s just 1mm stainless braided cable, but not sure other than that.  Is something as simple as this acceptable?
 

https://a.co/d/j8ZaL6Y

[FlyingMonkey]

I did some looking around, and I can't really find an "aviation grade" cable in 1mm (which is 5/128").  I found 1/32 cables, but that's 4/128 and probably not going to work. The 1/32 aviation grade cable has a break strength of 115lb.  The 5/128" cable I linked to above is rather to 140lb break strength with a working strength of 35lb, which sounds about right.

Any thoughts or ideas of a source for the "correct" cable type, or will just any 1mm 7x7 steel cable work?  Also, any tips on replacing the cable are appreciated.  I guess you fish it through the plastic cable sheath out to the carb, trim for length & heat shrink the ends, and then anchor at the throttle side.  The parts manual has some diagrams of the setup, but there is no specific procedure I can find in the Maintenance Manual. 

[Madhatter]

Standard aircraft cable is 7 x 7 stranded. 1 mm 7 x 7 in stainless is easily available and is rated at aprox 190 lbs. It's what I used, even Wallmart has it for $9.

[Tom Baker]

I have cable and stops, and routinely replace frayed cables.

[FlyingMonkey]

1 hour ago, Madhatter said:

Standard aircraft cable is 7 x 7 stranded. 1 mm 7 x 7 in stainless is easily available and is rated at aprox 190 lbs. It's what I used, even Wallmart has it for $9.

That's what I found online, 1mm 7x7 304 stainless 100ft for eight bucks.  So that is suitable? 

[FlyingMonkey]

50 minutes ago, Tom Baker said:

I have cable and stops, and routinely replace frayed cables.

What is the procedure for it?  As I described, just fish the cable through the plastic tube, trim to length, and terminate?  Any tricks to disassembly and terminating/attaching at the throttle lever?

[Tom Baker]

There is a stop on the inboard end. It goes through the little bulkhead forward of the throttle lever, around the little pulley on the throttle lever, and into the cable housing to the carburetor. A length of 1/16" heat shrink helps with getting the cable through the bulkhead, and everything else is pretty straight forward. I terminate the cable on the forward end by forging it with heat and a drill twisting and melting the cable. A third hand is nice for that process.

[FlyingMonkey]

2 minutes ago, Tom Baker said:

There is a stop on the inboard end. It goes through the little bulkhead forward of the throttle lever, around the little pulley on the throttle lever, and into the cable housing to the carburetor. A length of 1/16" heat shrink helps with getting the cable through the bulkhead, and everything else is pretty straight forward. I terminate the cable on the forward end by forging it with heat and a drill twisting and melting the cable. A third hand is nice for that process.

Thanks for that, great info!  How about the ferrule used to lock the cable?  Any particular spec or should I just use the ones that come with the cable?  They are aluminum IIRC.

[Tom Baker]

I use 1/16" copper cable stops from Aircraft Spruce. There is just enough room to pass through and back like the original. I can make you up a couple cables and send them to you.

[Anticept]

1 hour ago, FlyingMonkey said:

Thanks for that, great info!  How about the ferrule used to lock the cable?  Any particular spec or should I just use the ones that come with the cable?  They are aluminum IIRC.

Aluminum ferrules are the most commonly found, but they're also the weakest. You can find copper and stainless. If you go stainless, make sure the swaging tool you are using is capable of it... stainless is hard as hell.

Copper is more than enough for everything we use on flight designs for small cables.

[FlyingMonkey]

1 hour ago, Tom Baker said:

I use 1/16" copper cable stops from Aircraft Spruce. There is just enough room to pass through and back like the original. I can make you up a couple cables and send them to you.

Thanks for the offer, I'd like to try making them myself first, and if I hose it up badly enough I'll get them from you. 

Are these the 1/16" stops you use?

https://www.aircraftspruce.com/catalog/appages/nicopressstp.php?clickkey=3018679

I guess I'll also need a swage tool like this:

https://www.aircraftspruce.com/catalog/topages/nicopresstool.php?clickkey=16781

[Tom Baker]

Yes, those are the stops. I have a similar tool. You might also check and one of the home improvement stores. It wont be approved for certified aircraft, but it should work for this.

[FlyingMonkey]

23 minutes ago, Tom Baker said:

Yes, those are the stops. I have a similar tool. You might also check and one of the home improvement stores. It wont be approved for certified aircraft, but it should work for this.

Wilco thanks!

[Anticept]

3 hours ago, FlyingMonkey said:

Thanks for the offer, I'd like to try making them myself first, and if I hose it up badly enough I'll get them from you. 

Are these the 1/16" stops you use?

https://www.aircraftspruce.com/catalog/appages/nicopressstp.php?clickkey=3018679

I guess I'll also need a swage tool like this:

https://www.aircraftspruce.com/catalog/topages/nicopresstool.php?clickkey=16781

Going for that name brand swaging tool heh. It will outlive you and your next 5 generations though!

[Madhatter]

It's not the swaging tool type It's the go no-go guage that checks the sleeve compression for certified. We use copper Nicopress sleeves in certified, which will hold full strength on the cable.

[FlyingMonkey]

2 hours ago, Anticept said:

Going for that name brand swaging tool heh. It will outlive you and your next 5 generations though!

Well, I didn’t go for the $400 version!  I don’t mind Harbor Freight quality for a lot of stuff, but for something important like making sure your control cables stay attached, I’ll spend a bit more.

[FlyingMonkey]

I was able to get this done with no problems, thanks for all the information and advice guys!  It was actually much easier than I feared, you don't even have to remove the pulleys from the throttle arm to do it, just thread everything through.  And my stops came out good too, thanks for the advice on that Tom.

I went ahead and did both cables so they'll have he exact same cable type, stretch, and time/wear on them.

[Anticept]

By the way, the stop is only needed inside the cockpit, outside on the carbs I recommend leaving 2-3 inches extra and using a blowtorch and hand power drill to get that cable red hot and spin it off. Welds the end of the cable to a nice ball tip.

[FlyingMonkey]

19 hours ago, Anticept said:

By the way, the stop is only needed inside the cockpit, outside on the carbs I recommend leaving 2-3 inches extra and using a blowtorch and hand power drill to get that cable red hot and spin it off. Welds the end of the cable to a nice ball tip.

I spun mine and double heat-shrinked the ends to match how the previous cables were terminated.  I thought about torching them, but heat-treating a metal cable will transfer heat up the cable and could lead to brittleness.  At least that's what occurred to my lizard brain.  Maybe a little blob of JB Weld at the end of the cable would be a happy medium.

[Anticept]

It won't travel that far if you use a proper hot torch right at the end of the inner blue flame. It will melt and break within a few seconds, and it will only feel a little bit warm a couple inches back. That's why you leave a tail that's 2-3 inches by welding the end together.