Prop control knob hard to push/pull

jd21476

jd21476

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jd21476
My prop knob seems to getting stiff to push and pull. Is there some sort of lubricant that I can spray on it and work it back and forth to loosen it up?
 
jd21476 said:
My prop knob seems to getting stiff to push and pull. Is there some sort of lubricant that I can spray on it and work it back and forth to loosen it up?
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It might be getting rusty inside. If the outer plastic sheath on the cable housing is old and cracked, water gets in and starts rusting the housing and wire. If you find cracked or missing sheath, you could drip a bit of penetrating oil onto it and see what happens.

Another possibility is a melted plastic liner in the housing; some had nylon or some other non-heat-resistant plastic that would melt and start grabbing the wire. Running close to the exhaust system will do that.

But you might want to make sure, first, that it isn't the governor itself all gunked or dirtied up.
 
jd21476 said:
My prop knob seems to getting stiff to push and pull.
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What kind of cable is it: vernier or standard sheathed cable? Some cable types do not react well with certain lubes.
 
I would talk to my mechanic before applying lubricant. Could make it worse like bell says.
 
Its a vernier knob. It twists just fine but the first inch of the push pull seems to be getting stiff. The plane goes in for annual next month so Ill just ask my mechanic to check it out
 
Make sure it's not kinked. The best oil might be a penetrating lubricant. The penetrant will help it get through the outside of the cable (Assuming it is not covered.) and then the penetrant evaporates leaves the lubricating film. When oil gets old the light ends evaporate leaving really stiff stuff.
 
jd21476 said:
Its a vernier knob. It twists just fine but the first inch of the push pull seems to be getting stiff. The plane goes in for annual next month so Ill just ask my mechanic to check it out
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FYI: depending on the brand cable some can be lubed and some not due to the internal coatings. I'm sure your mechanic will sort it out for you.
 
Bell206 said:
FYI: depending on the brand cable some can be lubed and some not due to the internal coatings. I'm sure your mechanic will sort it out for you.
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Yup. Those with a nylon or teflon liner aren't helped by wicking lube into the housing. But sticky carb heat, mixture, and heating/cooling controls are sure fixed up if you wick a bit of MIL-PRF-7870 oil such as Royco 363 into them. That's the oil specified by Cessna and others as a general lube, and it lasts a lot longer than LPS of any sort. A quart of it lasts a long, long time. I used medical syringes with old LPS or WD-40 application tubes jammed into them to apply just a few drops in places tougher to get at.

Of course, sticking or rough carb heat and mix controls should be checked to see that the internal wire isn't corroded or worn by the housing due to vibration. A pitted or notched wire is likely to break and cause a lot worse problem than sticking.
 
For spiral wound steel engine control cables, it's best to lube them once in a while before they start to stick. Mouse Milk is also commonly used if minor sticking has initiated.

Once rust and/or excessive grit takes hold, the lifespan of the cable is limited. McFarlane sealed teflon lined control cables are pretty reasonably priced relative to aviation. o_O

You're making a guess/gamble the unseen inner-cable rust is benign. For me anyway... losing any engine control in flight due to weakening by corrosion isn't worth messing around.

Sometimes it's just worth listening to the warning signs and replace.
 
NordicDave said:
Mouse Milk is also commonly used if minor sticking has initiated.
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FYI: MM has toluene and other ketones in it. Unless your cables are old-style and made of only metal with no liners, I would not use it to lube control cables.
 
Necroing this thread... my plane has the spiral wound cables, no liner, no sheathing, no nothing. I noticed recently that the travel was feeling less than smooth and uniform. I shot all three with WD40 yesterday, which helped, especially for the carb heat, since I was able to shoot some directly inside as well. Now, I know the "WD40 is not a lubricant" mantra, but I do not have have a quart of MIL-PRF-7870 lying around (nor am I likely to). Is an LPS2 chaser appropriate here?
 
It’ll help until it makes it worse. Something that thin will flush out all the thicker stuff.
 
GeorgeC said:
but I do not have have a quart of MIL-PRF-7870 lying around (nor am I likely to). Is an LPS2 chaser appropriate here?
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FWIW: LPS-2 doesn't last. So unless you want to repeatedly apply it to get then same lube quality always best to stick with 7870 (Royco 363, Aeroshell 3, Brayco 363, NyCo 7870). Perhaps see if a local shop has some and will sell you a small quantity?
 
Years ago I was in our local (pre-Home Center) hardware store looking for some spray silicone. When I spotted a can that says "This is it!" on it. Curious, I looked to se what "it" was. Turns out it was what I was looking for. It was it!

1701007477304.png
 
Bell206 said:
FWIW: LPS-2 doesn't last. So unless you want to repeatedly apply it to get then same lube quality always best to stick with 7870 (Royco 363, Aeroshell 3, Brayco 363, NyCo 7870). Perhaps see if a local shop has some and will sell you a small quantity?
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I don't mind reapplying it periodically (quarterly? gotta do hinges, caliper guide pins, etc anyway...) as long as I won't dork anything up in the process. Yeah, maybe I can bum some 7870 off ye local shoppe...
 
GeorgeC said:
I don't mind reapplying it periodically (quarterly? gotta do hinges, caliper guide pins, etc anyway...)
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I've seen LPS-2 and similar products get washed out after only days. And if you dig deep enough, a number of OEMs recommend if a general lube oil (7870) is not available to use clean engine oil instead.
 
I’d disconnect it from the governor and confirm the problem is in the cable. Then I’d replace it.
 
Bell206 said:
FWIW: LPS-2 doesn't last.
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I’ve noticed that. I used it a few times to lube flight control (yoke shafts) and it didn’t seem to hold more than a week or so. Some dry silicone spray has given me much better lasting results.
 
I've never paid attention to the spray because when I help I'm usually doing plugs, but I know there is a lubricant applied to the throttle/mixture/prop every 50 or 100 hr inspection we do and out of 15 aircraft/10-15k hours per year I've never heard of sticking throttles.

Depending how often you fly, 50-100 hrs might be every annual, but lubricating parts that don't require dissamebly can be done under owner maintenance every x months too.
 
Bell206 said:
a number of OEMs recommend if a general lube oil (7870) is not available to use clean engine oil instead.
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Indeed, some Piper maintenance manuals say "Where general purpose lubricating oil is specified, but unavailable, clean
engine oil may be used as a satisfactory substitute."
 
I have a throttle cable that I don't think is as smooth as it should be. The mechanic said they are sealed, mostly. So for about $80 plus his time it will get replaced.
 
Get the cable replaced. I've had this problem twice...both with the prop and mixture...the failures only occurred on the ground, but that's what that means. AND it's probably because it is cold. When it is cold they do get more stiff and that is when the cables fail.
 
frfly172 said:
I leave the cables to the mechanic.
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I've now twice had relatives stay with me who told me "your toilet was running all night, so I closed the door so I couldn't hear it". Instead of jiggling the handle, turning off the water, or just asking me. If it were at their house, these kinds of people would probably call a plumber to fix it. If I were that plumber, I'd be annoyed.

Same thing for owners and mechanics, I imagine.

Over a whopping five years of ownership and a few different shops, my impressions:
* Mechanics MAY be willing to do SOME well-circumscribed things in exchange for money. It helps if you specify part numbers and diagrams, better still if you show up with the parts in hand BEFORE the work starts.
* Mechanics would rather not open up cans of worms, go on fishing expeditions, or fix things that are not broken.
* Mechanics would rather not deal with trivial things that owners can and should be doing themselves.
* Don't bother writing detailed bulleted lists of squawks, you'll only be disappointed when they don't make it to the work order. You want an annual? You're getting an annual. Sir, this is a Wendy's.

At the end of the day, you get what you get and you should be thankful that you got anything at all.

#itbelikethat
 
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