British Altimeter 6A/1743 dis-assembly

[VintageIron]

Hello, does anyone have information on how to dis-assemble the 6A/1743 altimeter? I have one that has a needle off.

Thanks!

 

[abaddon1]

6A/1743. Mk.XIII Altimeter. The front knurled bezel unscrews counter-clockwise giving access to the dial face. Be very careful; the graduations may well be Radium coated if they are a light beige colour. Not all were at this stage of the War.

 

[VintageIron]

Thank you very much for your reply! I have tried turning the bezel counter-clockwise, it won't budge, I even applied heat via a heatgun on low setting, it still won't budge. Would you have any other suggestions? The housing is bakelite? Would a chemical break free solution harm the material, something like Aerokroil? Thank you for the caution on the radium, it does have a a mix of white and light beige graduations, it's serial number shows a date of 1943.

 

[MiTasol]

British Instrument documents will provide you with more detail.

I would not risk further heat and I would be careful of using chemicals in general. I am not familiar with Aerokroil so cannot comment on it specificially.

Hopefully there is an instrument maker on the site who can provide experience based suggestions.

My thoughts would run towards something like an ultrasonic cleaner but I cannot see how to use it without the dial and other internals getting wet so obviously that is a no go.

 

[VintageIron]

Thank you for your reply, definitely would not use a heat gun, I used a hair dryer, to no effect, I did try the Aerokroil, keeping the unit face down so it would not drip into the unit, that also let the Aerokroil follow the threads, still not effect. There are no signs it was glued, but it acts like it was. I think next I'm going to use a hole saw in wood that will let me set the body through, then drill holes in the wood to put screws through the mounting holes in the unit, then make other holes near the squared off part of the body in the wood and put pegs around the body at support points, so that when I put a strap wrench on the bezel the twisting force isn't entirely on the units mounting points.

 

[MiTasol]

The problem is probably that the gasket between the bezel and the face has deteriorated and "glued" itself to the bezel and glass over the years. Maybe you could try a release agent to the gasket. I cannot suggest any though.

PS to me a hair dryer is just a low temperature heat gun.

 

[VintageIron]

The problem is probably that the gasket between the bezel and the face has deteriorated and "glued" itself to the bezel and glass over the years. Maybe you could try a release agent to the gasket. I cannot suggest any though.

PS to me a hair dryer is just a low temperature heat gun.

You're not wrong about the hair dryer, that's why I tried it rather than the heat gun I have, I was hoping that since the bezel is thin walled that the temperature change would cause it to expand more than the body. Neither the heat or the Aerokroil had any effect nor did they do damage. I read in the reply that had the pdf. on British altimeters, that the Mk.XIII is sealed, to prevent any false reading to the altimeter, that if they were reading faulty, they were not to be repaired at the air field, and were to be sent to the depot with a replacement installed, but there was no mention of what method was used to seal them.

 

[MiTasol]

I am fairly sure that there was a narrow rubber or similar compound thin flat gasket between the the case and glass and possibly between the bezel and glass on some models. That would have broken down over the years and become sticky and probably also leaked into the threads. It is a very long while since I had to work on one.
The AP section on page 338 shows an o ring that likewise would have broken down. It may have been natural rubber or Buna or some other compound so you would probably need to find something that will slowly penetrate and soften it.

 

[VintageIron]

I am fairly sure that there was a narrow rubber or similar compound thin flat gasket between the the case and glass and possibly between the bezel and glass on some models. That would have broken down over the years and become sticky and probably also leaked into the threads. It is a very long while since I had to work on one.
The AP section on page 338 shows an o ring that likewise would have broken down. It may have been natural rubber or Buna or some other compound so you would probably need to find something that will slowly penetrate and soften it.
View attachment 655945

Thank you! That was my guess to when reading the unit was sealed, but your reply answered the probable how of how it is sealed.