Compass demagnetized?

Taxying out on Saturday, on my way to the Ice Cream Social, I noticed that the compass was about 90? out. Tapping the glass didn't help.

On the flight the compass just seemed to randomly rotate as though it was completely demagnetised. I've never heard of this happening before. I haven't made any changes behind the panel since it was last working normally.

If it has demagnetised, does anyone know how this happened and can it be re-magnetised?

On a more positive note, it was my first long cruising flight since fitting a P-Mag and I got the EGT to come down from peak while leaning, on a carburetted O320, and fuel burn was about 10% improved cruising at 155 KTAS and 10,500'.

Yes, a compass can be re-magnetised. I even found an old 1950s vintage RCAF manual on line detailing their procedure for re-magnetizing an Airpath compass. Google is your friend, there are plenty of web sites and Youtube videos showing the process. You do have to be sure not to magnetize it too much, or it will misbehave in turns even more than usual.

If yours in an Airpath, you can get a rebuild kit from Spruce with the gaskets you need, and a half pint of compass fluid - or use lamp oil..

This solved my problem several years ago.

http://www.aircraftspruce.com/catalog/inpages/magneticcompassshield.php?clickkey=1813003

You might try taking a piece of steel and move it around the compass some to see if it affects it. I am not an expert on magnetism by a long shot but if it was recently working and all of a sudden just quit I would look hard for something else first. Do you have another compass you can swap out to see it it has the same problem?

Charles - good point about trying to move the compass with some ferrous metal. I'll investigate further next weekend when I get a chance to go back to the hangar. What seemed odd was the fact that the compass rose moved freely but with no tendency to return to a heading.

That suggests to me that either there is no magnetic field to move the compass or that the compass is insensitive to the magnetic field.
But it was working on the previous flight and I haven't changed anything since.

I'll take it out and bench check it, and report back if I discover the cause.

I have been thinking about this today and wondered, could the magnet have come loose from the compass card? I have no idea but I am sure that different manufacturers have different ways of attaching the two parts.

Mystery solved!

In the hangar today, I tried to see if the compass would respond. I used my magnetic pickup tool and brought it close to the compass. Initially the compass card tilted, then suddenly jumped in response to the magnet.

Something obviously wrong, so the compass came out and got disassembled. At first I could not find any fault as the card appeared to move freely on the jewel post and lined up correctly with north. I then got suspicious of the diaphragm. Reinserted the diaphragm guard and diaphragm and the card hung up on what was now easy to see as a swollen and mis-shapen rubber diaphragm.

Maybe it had been re-filled with an incorrect fluid at some time and that had swollen the diaphragm. Anyway the repair kit that ACS sell should fix that and I found a second hand compass for $30 on VAF that will do in the mean time.

Pictures of the diaphragm etc on https://drive.google.com/open?id=0B6m6wa17VEsCb0pkN214eVEtczg&authuser=0

I have read that those diaphragms don't last more than a few years. Don't know how true that is. Mine is the military version with a bellows instead of a diaphragm... for which there are apparently no repair parts available. Glad you found the problem.