Throttle cable suddenly very stiff overnight

[Sportquattro]

Just been doing my annual condition inspection on my RV9A with a O-320-D2A. On Wednesday we checked all the cable operations and everything was super smooth, the very next day when the LAA Inspector was signing everything off the throttle was VERY stiff to operate. We have checked everything for any cable kinks or other obvious issues and can find none. Even with the friction nut backed right off its the same.

This has happened once before about 8 months ago, and the next day it was fine again. The cables are McFarlane one and the aircraft has flown just 100 Hours since completion 2 years ago.

If any of the Vans collective genius minds have any thoughts then please let me know as at the moment we are baffled.

Thanks in advance

Nige

RV9A G-CSAM at EGTE UK

 

[D-Dubya]

Disconnect the cable connection at the throttle and see if you can isolate the sticking to the actual throttle or something within the cable. If it's happened before, it'll likely happen again. Keep moving the cable and the throttle independent of each other and maybe the problem will repeat.

Not sure where to look if that comes up empty. Could it be going over center? Is the throttle knob independent of the other controls or part of a quadrant?

 

[Tailwind/RVGuy]

Disconnect the cable connection at the throttle and see if you can isolate the sticking to the actual throttle or something within the cable. If it's happened before, it'll likely happen again. Keep moving the cable and the throttle independent of each other and maybe the problem will repeat.

Not sure where to look if that comes up empty. Could it be going over center? Is the throttle knob independent of the other controls or part of a quadrant?

X2 on David's comment. About 1 year ago, I had gotten some fuel contamination which apparently was some sort of bacteria that made it's way through my fine mesh filters into the carb where it grew and caused severe corrosion in the carb INCLUDING THE ACCELERATOR pump. I had the same problem of very stiff throttle cable and when I disconnected it from the carb, I was barely able to move the throttle lever due to the accelerator pump being corroded. $500 later, a carb overhaul and total fuel system cleaning in my plane all was good. By removing the connection, you can at least isolate where the problem lies.

As an aside, this fuel contamination issue was very strange and caused a lot of grief. I would have never guessed that this could happen in avgas but it did. Experts that I had talked to had never seen anything like it. It was a private tank at an airpark so not from a public source. The tank had been cleaned and in our opinion was not done properly.
Keith

 

[AZSteve053]

#1. Engine control cables have been known to become very stiff if the inner lining gets too warm - partially melts and cools while gripping the center sliding cable. When engine heats up on next start problem most often clears at least temporarily until the cable completely cools again.
#2. Engine cables have been known to freeze when high humidity air permeates the cable assy during above freezing conditions - then freezes solid when temps drop resulting in a temporary locked cable.
Disconnecting the affected cable from the controlled item, in this case carb throttle lever, allows for isolation of culprit to cable or controlled item.
Good Luck.

 

[markduffield]

I had the same problem and it was the cables being overheated and causing them to get stiffer and stiffer over time as the inner plastic sleeve began dragging on the actual cable. Nothing to fool around with. I replaced all of the cables, firesleeved them and wrapped them with aluminum tape. All good for three years now.

 

[wawrzynskivp]

Just a data point that's been shared here before:

I had a throttle cable jam at the swage end near the fuel servo at around 20-25 hrs of use. I was very fortunate that it jammed on the landing transition, for once it was jammed that was it for any motion beyond the swage at the fuel servo side. You could still feel some springiness in the cable up to the jam, but no motion beyond that. The cable was installed very nearly straight from a center console forward, right on centerline between the exhaust and was heat shielded. A replacement cable has worked fine in the exact same configuration for five years since.

Looking backwards with hindsight I believe I did notice a small change in friction preceding the jam. My thoughts are to pay very serious attention to any mystery friction on the throttle cable and not to accept anything less than what you expect for that particular cable.