rebuild a compass

[mulwyk]

My old airpath has a cracked lens and slooow leak. I got a Wag Aero rebuild kit for it (very reasonable, $12.85 including shipping). Any tips on rebuilding an old compass? Any way I can really mess it up? What's everyone use for compass fluid...whiskey? or is that just a myth?

[NY86]

Re: rebuild a compass

Clear (white?) kerosene.

I've heard of folks using mineral spirits, but don't know...

Of course, you're referring to the compass on your tractor, right? Not even an A&P can work on the compass on a certificated aircraft!

[mike lutz]

Re: rebuild a compass

I read on one of these post some where that Johnson baby oil is the best compas fluid you can use.

[Robert Lees]

Re: rebuild a compass

I read on one of these post some where that Johnson baby oil is the best compas fluid you can use.

Another vote for Johnson Baby Oil (available from wheelbarrow oil lubricant suppliers).

[Pearson]

Re: rebuild a compass

I have worked on several compasses. I have never used Johnsons Baby oil, but it sounds like it might be a good idea. I tried mineral spirits and it washed the ink off the heading indicator wheel inside, or maybe that was the denatured alcohol I tried.

I can tell you from experience, if you are replacing a broken glass you have to be EXTREMELY careful to remove all microscopic shards of glass from the mounting surface where the new glass sits between the two gaskets. The most microscopic spec of glass left under the gasket will cause the new glass to break.

As an aside, you don't have to pay $21 or whatever it is these days for a little piece of glass and a new gasket. I went to a glass shop to buy a piece of glass. When they saw how small a piece I wanted, they pointed to the scrap bin and said help yourself. I bought a glass cutter for $4 and cut the glass myself. The sides were curved so I made a three edged cut on each side and ground it to an arc to match the compass housing with a dual action orbital sander (DA sander used by bodyshops to sand cars for painting). I wore gloves and safety glasses and with 220 grit paper it only took about two minutes for each side. Of course the first one didn't match the radius, neither did the second one. But by the third one I was having so much fun I made an extra. You have to lock the wheel on the dual action sander to make it a single action, like a grinder. Or if you have one of those circular sanding contraptions used in woodworking that would work. I don't know, but even a belt sander might work.

Caution, the glass gets very very hot. You need to wear gloves. I tried to use the gasket to draw the outline of what I needed, but I couldn't get anything to write on the glass. Tape kept curling up when I drew the outline on it, so I just ground a little and checked it, then ground a little more. That seemed to be the best way for me.

I also had to adjust the compensating screws. It is easy. After it was reinstalled, I used a hikers compass to adjust the aircraft compass to match. I did it with the aircraft pointing north, then did it with the aircraft pointing south. I realigned the aircraft north and it was still dead on. I checked it both east and west and several points in between. I think I saw a one degree difference on one heading. Piece of cake!

[astjp2]

Re: rebuild a compass

Says Who?

Not even an A&P can work on the compass on a certificated aircraft!

[Hank Jarrett]

Re: rebuild a compass

I had an IA show it to me in the FARs. As many things as I fix myself on my plane (including the compass in the past) I sent mine off to Keystone and got it yellow tagged.

Home repairs to compasses seem really common, but I guess we have to put the repaired ones on our wheel our wheel barrows to be legal. Might explain why leaking compasses are so common.

Anybody know where in the FARs that restriction is?
Hank

[dalijohn]

Re: rebuild a compass

Hank, look at FAR 43, Appendix A(b)(4)(i)

"Appliance major repairs. Repairs of the following types to appliances are appliance major repairs:

(i) Calibration and repair of instruments."

[Hank Jarrett]

Re: rebuild a compass

That would cover it, but I thought it was more specific than that. Interesting thing is that one would prevent you from even centering a ROC needle with the little adjuster screw in the lower left mount hole. There is no knob for the pilot and it takes a tool so I would think it might fall under "calibration" if the IA was a stickler.
Hank

Don't let anyone see you do it.

[Forrest Barber]

Re: rebuild a compass

They become sticklers right after the accident involving a suit happy dead passengers family members.
"Compass fluid" can be purchased lots of places. to get the compass "full" requires a knack , in the old days when we ( A&P) could do this major repair we would have a can of compass fluid and submerge the whole thing till the bubbles stopped. there is a bladder in the system that comes with the repair kit. I am going to my IA refresher in two weeks and will talk with the CLE FSDO & MIDO about a lot of things.

[astjp2]

Re: rebuild a compass

You actually have a IA refresher in your region? Wow, I thought that alaska was the only one left to have the budget. Tim

[magman]

Re: rebuild a compass

FSDO 23 ( Rochester NY) has had a Refresher for several years that is combined with other activities on the airport.

I have a copy of a hearing involving an A & P that was foolish enough to sign off a compass repair. Not nice.

There were folks in this area that had a "Magnetic Compass Overhaul
Repair Station".

It consisted of a Card Table & :

1. A Bowl ( per Forest) & contained parts & can of fluid

2. Compass Repair & Parts Manuals

3. Repair Station Maual & Work Orders.

[freightpilot27]

Re: rebuild a compass

We have had one here in the Detroilet area too.

http://www.greatlakesaviationconference.com/maintenance.php

[Forrest Barber]

Re: rebuild a compass

My IA renewal is 2-13-10 ; CLE FSDO , I have been going to renewals since 1950 with my Dad , an original DAMI ; I was 8 yrs old at the first one...
We just got hit with the snow event hfere in Alliance, everytihing is at a stand still out there . I will fire up big tractor and get started clearing things here sonn!

[mulwyk]

Re: rebuild a compass

Thanks Forrest for the "submerge the whole thing" tip. That works great. The picture shows a compass (a boat compass) submerged in baby oil. I used the bottom half from a 2 quart plastic milk bottle and 20 oz. of baby oil, both from WalMart (the compass came from a boat).

Baby oil is a bit more viscous than the kerosene that was originally in the boat compass. The thicker baby oil makes the compass slower moving and more stable. It's less prone to overshoot the heading and less inclined to hunting and spinning. That's good and my impression was that the baby oil had improved the compass.

However, I was a little worried that baby oil might be too viscous at low temperatures. So last night we set the boat compass outside...it was about 5 below. When we brought it back inside this morning it's operation was definitely sluggish. It took 90 seconds to turn through 180 degrees. After the compass warmed to room temperature it would turn the 180 degrees in about 20 seconds. My conclusion: baby oil compass fluid is great at normal temperatures but might not be best for folks who go boating in very cold conditions.