Master Switch Piano Key Failure

How to keep the Cessna 170 flying and airworthy.

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Ragwing48
Posts: 3
Joined: Mon Nov 28, 2022 2:24 pm

Master Switch Piano Key Failure

Post by Ragwing48 »

Hey Guys and Gals,

I've been having intermittent issues with my "piano key" master switch as last summer. It has trouble making connection and usually takes a couple flicks to get it to work. (at which point no issues arise after it works)

I used contact cleaner last year which temp fixed the issue but its back again. I searched the forums for piano key and found numerous discussions but nothing that worked for me.

My question is.... does the entire piano key assembly have to be removed to work on fixing this issue? If so how many hours ballpark am I looking at for an AME to complete this rather simple yet "pain in the ass" fix.


I appreciate the insight from everyone.


Kyle
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GAHorn
Posts: 20914
Joined: Fri Apr 12, 2002 8:45 pm

Re: Master Switch Piano Key Failure

Post by GAHorn »

The ‘piano key” is merely a lever (Cessna calls it a “handle”…item 58 in the Figure) …which actuates a common toggle switch (item 66…not actually well-illustrated) …hidden behind the panel. The Cessna part no is AN3027-1.

Aircraft Spruces sells them, less than $20. Depending on your skills… one to two hours.

There’s a good chance that the rubber “grommet” which fits at the end of the lever is worn…and cannot reliably activate the switch fully…and may be the problem. So look at that. A new grommet may remove the “slop” that prevents full-activation of the toggle. If you replace the switch…replace the grommet also.

The grommet: https://www.aircraftspruce.com/catalog/ ... 31-4-7.php

The switch : https://www.aircraftspruce.com/catalog/ ... 3027-1.php
72059444-7B2F-4930-8C78-4A73B92B74F3.png
'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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dstates
Posts: 470
Joined: Sun Jun 30, 2019 5:50 pm

Re: Master Switch Piano Key Failure

Post by dstates »

Beware, to remove the piano keys you need access to two screws that are behind the plexiglass on the panel (one on each side of the throttle). You can either remove the plexiglass (which requires messing with throttle, mixture, etc.) or you can drill holes in the plexiglass where the screws are to be able to access them. I decided to drill holes in the plexi. However, I didn't realize that it took a special drill bit when working with plexiglass and on the second screw (first one went fine) it grabbed and cracked. It would have been perfect if I had used the right drill bit. A good drill bit for plexiglass is a step drill.

Check out this thread:
viewtopic.php?f=24&t=4718

Doug
N1235D - 1951 170A - SN: 20118
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GAHorn
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Joined: Fri Apr 12, 2002 8:45 pm

Re: Master Switch Piano Key Failure

Post by GAHorn »

Good advice from Doug. Another “trick” which has worked for me when drilling plastic is to take a good bit and simply grind the point “flat” on the bench-grinder. The flat point prevents the bit from “biting” too aggressively into plastic thereby cracking it. Does a fine job.
'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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