Mixture Cable Attachment

How to keep the Cessna 170 flying and airworthy.

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minton
Posts: 764
Joined: Wed Mar 23, 2005 2:20 am

Re: Mixture Cable Attachment

Post by minton »

OBTW: This has always had the potential for a disasterous failure in flight senario. I wish that someone would develope a fix.
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GAHorn
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Joined: Fri Apr 12, 2002 8:45 pm

Re: Mixture Cable Attachment

Post by GAHorn »

An ordinary tension spring attached to the arm and to a nearby tab or assy screw should do the trick.

But my favorite fix for "bug nuts" (drilled bolt/washer setups) is to pass the wire thru the bolt hole...then, before cutting the wire or tightening down on the nut/washer... to wrap the wire around the bolt at least one turn, preferably 1.5 turns. That way, even if the nut comes off...the wire will retain the bolt and remain on the carb lever.

One problem with the factory setup is the washer ID has a sharp edge which, when tightened down on the wire, places a "cut'" or stress-riser on the wire. Wrapping the wire around the bolt-shank after passing it thru the hole resolves that issue because the nut does not have to be torqued tightly onto the wire. IN other words, the nut isn't even necessary for the wire to remain in the bolt, and the bolt rotates freely in the lever.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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blueldr
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Joined: Thu May 02, 2002 3:16 am

Re: Mixture Cable Attachment

Post by blueldr »

George,
With the Bowden wire wound around the bolt, how do you take it apart for maintenance or repair of the carburetor?
BL
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jwsowles
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Joined: Fri Dec 25, 2009 6:10 pm

Re: Mixture Cable Attachment

Post by jwsowles »

It was that washer that cut/broke my cable, so I like George's suggestion about wrapping the cable and torquing firmly, but less. I'll also be smoothing/rounding the washer and putting on a light tension spring. If anyone has specific details or experience, let me know.
John
N3487D '56 170B
N1427E '46 7AC
N36805 '41 BC65
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n2582d
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Joined: Mon Apr 29, 2002 4:58 am

Re: Mixture Cable Attachment

Post by n2582d »

I see that Aircraft Spruce also has a "Cable End 'B' Nut" for this sort of application. Probably need to get some sort of approval basis to use it. I'd also want some way of insuring the the allen screw doesn't come loose.
05-16210.jpg
Gary
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GAHorn
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Re: Mixture Cable Attachment

Post by GAHorn »

blueldr wrote:George,
With the Bowden wire wound around the bolt, how do you take it apart for maintenance or repair of the carburetor?
Once wrapped, the central wire of the Bowden cable is not re-useable. But it's also unlikely to often need removal. In any event, it's a simple matter to purchase another cable and insert the new wire thru the existing cable-housing, for replacement puroses. They are not expensive. (less than $28)
Image

http://www.aircraftspruce.com/catalog/appages/a730.php

One more thing: In order to protect from breakage as I suggested, one of two methods must be utilized. 1-the wire must be wrapped around the bolt...with the wraps on the NUT side of the thru-hole. (If the wire is wrapped toward the lever, the nut will still be able to cut the wire where it passes thru the bolt.) 2- the wire could be wrapped, THEN passed thu the hole (very difficult to accomplish due to the stiffness of the wire.)
The "bug nut" shown above also stresses the wire where the screw "smashes" against it.

This scenario occurred when our friend Bob Lavery was checking out in my airplane in preparation for the right-seater's course at GLS convention. He was pulling rather timidly on the starter-cable when I admonished him to "PULL IT! You're NOT going to HURT it!".
He did, and it promptly snapped.... allowing the back of his clenched-fist to strike me in the chest nearly knocking the wind out of the guy who had shouted at him. :lol:

It was a very hot day, and after much hand-propping the still-hot, reluctant engine, I was worn out and my hands destroyed with blisters from the prop-edge, and we were both disgusted....me with frustration my engine would not start... Bob disgusted with me.

Image

That's when Bob suggested that instead of hand-propping the engine, .... that I should instead simply reach thru the opened cowl-door and operate the start-lever to which the broken pull-cable was formerly attached. 8O

Voila!

How does this story relate to the subject at hand???
The starter pull-cable wire was broken exactly where the nut held it as it passed thru the bolt attaching it to the pull-starter-lever. I purchased a new cable, removed it from it's housing, and inserted the knob/wire thru the already-installed, old cable-housing, and wrapped the wire around that lever-attach-bolt. (I actually passed the wire thru the bolt-hole, then one wrap on the head-end of the bolt-shank, another wrap on the nut-end of the bolt-shank, and cut off the excess wire and installed the nut. Placing two wraps, one inside, one outside of the wire-hole imparts a more "balanced" (non-twisting) "pull" on the bolt and lever.) I expect that starter pull-cable to outlast all others.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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