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The second instrument that I bought off eBay was an unserviceable Mk 1B 6A/1519 Attitude Indicator/Artificial Horizon. You can see a spare bit floating around the front !
Now there are a large number of these on the market - but absolutely no documentation or engineering drawings freely available. So after a lot of fiddling around I eventually worked out a method to dismantle it and then realised it may have been worth documenting it for any one else who fancies taking one to pieces. So I have retrospectively taken some photos and will describe the basics of taking it to pieces here.
Not absolutely necessary but you can remove the air filter assembly to give you a level base for working off. Use some circlip pliers to remove the circlip and then pull out the brass filter. The filter holder can then be removed by undoing the 5 screws holding it.
Removing the 6 screws around the outer rim will then enable you to remove the back cover and gain access to the internals.
Note: this shows the position of the outer cage (without the gyroscope or horizon lever which have been removed). The rear bearing for the cage is in the outer cover (lid) and the pin on the cage - the front is the reverse of this with the bearing in the cage and the pin on the arm coming down from the top of the casing. This arm is part of the casting and is not removable. Two other points of note a) there is a slot cut into the right hand side of the casing face to accommodate the smaller of the two gyroscope bearings and allow the cage to eventually be eased through b) internally on the right there is a leaf spring and a matching external screw which can be used to push the spring out (I assume to lock the cage for shipping and not to adjust the internal airflow).
I could find no way to remove the cage backwards out of the case as the horizon plate is fitted to the cage in front of the forward bearing arm.
With the 7 screws holding the front cover/glass in place removed you can gain access to the horizon bar and plate - This photo shows the 2 location pins and two bolt holes that hold the horizon plate in place. These need to be unscrewed and the plate removed to enable the cage to removed from the rear. You can see the extra hole that I drilled to get easy access to the bolts ! You could alway countersink and tap this block it after reassembly.
Not a good photo here as the horizon indicator is upside down and should be at the bottom of the photo. The hinge is at the top next to the blue bolt. The pin goes into the gyroscope to the right of the bearing and pushes through the channel on the left side of the cage and then through the central slot in the indicator.
To remove the gyroscope from the cage you need to first remove the indicator pin then back off the bearing pin on the left side of the cage. Not having the correct tools to do this I resorted to brute force.
Here you can see a cross section through the gyroscope
To remove the gyroscope from the cage you need to first remove the indicator pin then back off the bearing pin on the left side of the cage. Not having the correct tools to do this I resorted to brute force.
Here you can see a cross section through the gyroscope
I never did find where that spare part went !
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