My Master Switch (on the instrument panel) needs to be replaced. I've checked the Battery Solenoid and it's OK. The switch I need to replace is the "piano key" type and the part number from the "IPC - Model 170A" lists the part as AN3027-2.
My question: Is this the right part number? I went to the Aircraft Spruce website and looked at the graphic of the part and it has a toggle type switch lever on it. Is this toggle lever just something I can't see from the cockpit? I have the "piano keyboard" type of switches. My understanding is that I only replace the "rear" part of the switch, not the piano key, but I want to make sure I get the right part.
Any ideas? How about time to replace?
Thanks,
Master Switch - C-170A
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Mike Smith
- Posts: 175
- Joined: Mon Jun 02, 2003 2:53 pm
Master Switch - C-170A
Mike Smith
1950 C-170A
1950 C-170A
Hi Mike,
First, make extra sure that the solenoid is ok. I had the same problem last year with a one year old solenoid and it turned out that it was bad, not the switch.
Yes, that's the right part and Yes it's something you can't see from the cockpit. I've become pretty familiar with this assembly recently as I've taken out my panel and we've replaced the grommets on all the piano keys.
The way it works is this:
The piano key extends behind the panel about as much as it extends in front and pivots in the middle on a rod that connects all the keys. Behind the panel, the piano key bends downward at a little more than 90 degrees. This "almost vertical" section has a hole in the center approx. 5/16 in diameter. The toggle from the switch protrudes through this hole and the gap between the toggle and the edge of the hole is taken up by a grommet. When piano key is switched "on" (down) the hole in the piano key "cams" against the toggle throwing it UP and turning on the circuit. Your IPC should have a drawing of this assembly.
Replacing will be... (ahem), "fun". The entire switch assembly will need to be removed from behind the panel in order to do this. Once you have this out, you can get at the switches. The switches are installed on a bracket assembly and the nut that holds on the switch is located between the bracket and the back of the piano key. Get in there with a thin wrench loosen the nut that anchors the switch. Once you get the nut off, the switch will come out the back of the assembly. Of course, the switches are all still wired at this point, so it only hangs down a few inches which means you'll be doing all this in the cockpit in some semi-contorted position. Do some good stretching or yoga before starting this.
If your piano keys don't line up when viewed from the front, this would be the ideal time to change all the grommets on the back and get them lined up again. They are only $.09/ea from Spruce. Get rid of that retired hockey player look.
Have fun!
First, make extra sure that the solenoid is ok. I had the same problem last year with a one year old solenoid and it turned out that it was bad, not the switch.
Yes, that's the right part and Yes it's something you can't see from the cockpit. I've become pretty familiar with this assembly recently as I've taken out my panel and we've replaced the grommets on all the piano keys.
The way it works is this:
The piano key extends behind the panel about as much as it extends in front and pivots in the middle on a rod that connects all the keys. Behind the panel, the piano key bends downward at a little more than 90 degrees. This "almost vertical" section has a hole in the center approx. 5/16 in diameter. The toggle from the switch protrudes through this hole and the gap between the toggle and the edge of the hole is taken up by a grommet. When piano key is switched "on" (down) the hole in the piano key "cams" against the toggle throwing it UP and turning on the circuit. Your IPC should have a drawing of this assembly.
Replacing will be... (ahem), "fun". The entire switch assembly will need to be removed from behind the panel in order to do this. Once you have this out, you can get at the switches. The switches are installed on a bracket assembly and the nut that holds on the switch is located between the bracket and the back of the piano key. Get in there with a thin wrench loosen the nut that anchors the switch. Once you get the nut off, the switch will come out the back of the assembly. Of course, the switches are all still wired at this point, so it only hangs down a few inches which means you'll be doing all this in the cockpit in some semi-contorted position. Do some good stretching or yoga before starting this.
If your piano keys don't line up when viewed from the front, this would be the ideal time to change all the grommets on the back and get them lined up again. They are only $.09/ea from Spruce. Get rid of that retired hockey player look.
Have fun!
Last edited by doug8082a on Fri May 28, 2004 12:52 am, edited 1 time in total.
Doug
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Mike Smith
- Posts: 175
- Joined: Mon Jun 02, 2003 2:53 pm
There's one grommet per switch on the "nearly vertical" part of the piano key. When you remove the switch from the bracket, the piano key will spin freely on the pivot rod. Just rotate it 180 deg., change the grommet, rotate it back, and reinstall the switch. The old grommets will likely be hard and dried out. I used a small flat bladed screwdriver to push the grommet out. The new ones are nice and pliable and will pop right in.
Doug
Just checked my IPC - I have a '52 B which has the same panel layout and piano keys as your "A". Interesting that my master switch is a AN3027-1 and yours is a -2. Wonder what the difference is.
If you want to get a look at the assembly, just grab a flashlight and lay down in your cockpit and look up. The assembly is visible from below.
Also, when you take the switches out there will be a "J" shaped clip under the nut that holds the switch to the bracket. Don't lose this. Also, be sure to reinstall it as a "J" - in other words DON'T turn it over("r") . The switches are actually three-position switches: Up - On, Down - On, Middle - Off. The "J" shaped clip prevents the piano key from moving UP and thereby throwing the switch down (since these switches each perform only one function). If you install the "J" upside down ("r") it will prevent the piano key from moving DOWN to turn on the circuit.
The only time that I know of that it was valid (from the factory) to use both the Up and Down portion of the switch was if you had the Stewart Warner cabin heater installed (which was in mine from the factory). Then you had Up for "Fan" (to prime the heater), Down for "On" and "neutral" for "Off".
I suppose you could remove the clips if you wanted to make use of the extra function for, say landing/taxi lights. Maybe Up for taxi only and Down for both. Or if you had a beacon and wingtip strobes you could wire it as Up for beacon only and down for All. I've thought about doing that a couple times, just never got around to it.
If you want to get a look at the assembly, just grab a flashlight and lay down in your cockpit and look up. The assembly is visible from below.
Also, when you take the switches out there will be a "J" shaped clip under the nut that holds the switch to the bracket. Don't lose this. Also, be sure to reinstall it as a "J" - in other words DON'T turn it over("r") . The switches are actually three-position switches: Up - On, Down - On, Middle - Off. The "J" shaped clip prevents the piano key from moving UP and thereby throwing the switch down (since these switches each perform only one function). If you install the "J" upside down ("r") it will prevent the piano key from moving DOWN to turn on the circuit.
The only time that I know of that it was valid (from the factory) to use both the Up and Down portion of the switch was if you had the Stewart Warner cabin heater installed (which was in mine from the factory). Then you had Up for "Fan" (to prime the heater), Down for "On" and "neutral" for "Off".
I suppose you could remove the clips if you wanted to make use of the extra function for, say landing/taxi lights. Maybe Up for taxi only and Down for both. Or if you had a beacon and wingtip strobes you could wire it as Up for beacon only and down for All. I've thought about doing that a couple times, just never got around to it.
Doug
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zero.one.victor
- Posts: 2271
- Joined: Tue Apr 23, 2002 12:11 am
My ragwing has been fitted with leading edge taxi/landing lights,and the piano-key switch is rigged to flip up for landing light & down for taxi light.
Also,it may seam like a no-brainer,but I advise anyone doing any work under the panel to just take the few minutes required to remove the front seats first. It's not much of a job & your back will thank you. If you have to make many trips up & out to the toolbox & then back under the panel,it'll actually save you time too.
"Old Creaky"
Also,it may seam like a no-brainer,but I advise anyone doing any work under the panel to just take the few minutes required to remove the front seats first. It's not much of a job & your back will thank you. If you have to make many trips up & out to the toolbox & then back under the panel,it'll actually save you time too.
"Old Creaky"
Hadn't thought about it, but that's an advantage that George has in that old beat up B of his. 
. . . He can jump out while in flight and run over to the toolbox, then run and catch back up with his plane and work on it some more. Or, just stand there with a polishing rag, and hold the rag up against the plane while it slowly flies by . . . 
. . . He can jump out while in flight and run over to the toolbox, then run and catch back up with his plane and work on it some more. Or, just stand there with a polishing rag, and hold the rag up against the plane while it slowly flies by . . . Joe
51 C170A
Grand Prairie, TX
51 C170A
Grand Prairie, TX