Hints on refilling an Airpath compass?

Anyone ever refilled an Airpath Panel mount 2 1/4 inch compass?
I have the rebuild kit from Aircraft Spruce, but no directions.

Seems pretty simple, I already have the front and rear off. Is the big screw on top the recommended fill port? Did not get a gasket for that in the kit.

I have front gaskets (2) and rear diaphragm plus fluid.

Airpath compass

Its been awhile since I re-filled mine but IIRC, the big screw is where you fill it.

It was a tough screw to get loose.

Dave
-9A flying

Airpath

Thanks for the tip. I just found an EAA article:
http://www.eaa448.org/Downloads/EAA448May09.pdf

That's a really good article, by Gary Sobek. One thing I tried, that worked, and not mentioned in his article, was to fill up a small "tub" with the compass fluid, then submerge the entire compass in the fluid. Gets the bubbles out the easy way.

You do have to have enough fluid to do that, but the tub only has to be barely big enough to hold the compass. I re-attached the fill port while the compass was submerged.

PCHunt said:

That's a really good article, by Gary Sobek. One thing I tried, that worked, and not mentioned in his article, was to fill up a small "tub" with the compass fluid, then submerge the entire compass in the fluid. Gets the bubbles out the easy way.

You do have to have enough fluid to do that, but the tub only has to be barely big enough to hold the compass. I re-attached the fill port while the compass was submerged.

Click to expand...

The only reason that I did not do that when I wrote the article was because I was too cheap to buy more fluid.

i heard of a neat trick. use Johnson's clear baby oil for the fluid. it will damping out the turning errors of a magnetic compass.

Try vacuum

During my Air Force days we used to submerge a freshly rebuilt "whiskey compass" in a container of compass fluid with the fill port loose. We would then close the container and pull a vacuum on the vessel. After equalizing the vacuum we would tighten the fill port while still submerged. Worked on B-52s and F-4Ds that I know of.
Possibly another use for your vacuum bagging pump.

How do I open the case on an airpath C3250 compass so that I can access the fill screw? It is the panel mount and doesnt have any visible cap. It is just has a rounded bulb.
Thanks

What....No single Malt jokes?

I like the baby oil idea, will that become to viscous in cold weather?

rhill said:

I like the baby oil idea, will that become to viscous in cold weather?

Click to expand...

good question. will have to wait for someone to try it. i have a supply in my hangar in case i need to replace mine. also comes in handy to sooth down my girl friends sore muscles.

Mineral spirits or varsol is all shops that I worked in ever used.

compass

sglynn said:

How do I open the case on an airpath C3250 compass so that I can access the fill screw? It is the panel mount and doesnt have any visible cap. It is just has a rounded bulb.
Thanks

Click to expand...

I'm not sure about that exact model, but most compasses that are covered by a mounting case have a screw at the back. Remove the screw and the compass should slide out the front of the case/bulb.

Open compass and won't point north

Yes, but no screw. I was able to send a photo to mfg help desk and they told me only way to fill it is thru front plate where glass goes. I was able to do it totally submerged in the oil and got it closed up with no bubbles. But no when I test it, it doesn't point N, S, E, W very well. I tried standing on my back deck to align it with no interference and it doesn't align. Oh well.

Any ideas on how to re-strengthen the compass magnet so it points north with more force?

thanks

Aw, compass juice is pretty cheap. I've repaired a few compasses and I've never taken out the big screw on the top. It's not supposed to be a fill port. It actually holds the jewel for the card to turn on. If the compass is low on fluid, the diaphragm is almost certainly bad and just refilling it will not last long. In A&P school we were taught to remove the rear cover and little the metal bit on the diaphragm. If the compass was (is?) leaking, you'll find a perished diaphragm. Toss the diaphragm. Replace the gasket on the front glass as well. Gaskets and diaphragms are cheap, you're here and the tools are out. Submerge the compass in new compass fluid (gloves, or at least clean hands, OK?) and reinstall the back with a new diaphragm. Roll it around a bit to get all the bubbles out before you tighten the screws while the compass is still submerged. Take the compass out of the container, reinstall whatever else is needed, dry it off and you're good for a few more years.
BTW, you should swing the compass after doing this. If you don't know how, just google 'aircraft compass swing' for a couple of different methods. Not difficult at all.