rebuild a compass

[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

[astjp2]

Re: rebuild a compass

Says Who?

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

[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!

[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).

[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.

[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!

[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?