The International Cessna 170 Association

OBTW: This has always had the potential for a disasterous failure in flight senario. I wish that someone would develope a fix.

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.

George,
With the Bowden wire wound around the bolt, how do you take it apart for maintenance or repair of the carburetor?

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.

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.

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)


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.

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.



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.

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.