NavList:

Hi, you were describing a familiar problem, maybe late but here my comments:

You have one of the sophisticated Mark IX ,s where the fine setting gear can be adjusted to smooth as silk, but your adjustment is way off.

Take off the right handle , three screws note that the rear screw is shorter. The grip will be free except for two wires to the lamp.
Take off the fine setting knob, one center screw.
Now you have access to the screw of the intermediate gear cluster. If this screw is loose than you will experience a gear that hangs and rattles in both directions. Newer mind it must be adjusted anyhow. The intermediate gear cluster is fastened with the screw, a bush and under the bush against the casing a locking washer, check that bush and washer are present.
Note that the inner diameter of the bush is considerable larger than the diameter of the screw. This allows the intermediate gear to be adjusted in correlation to both the gear box input gear and the gear of the fine setting knob. Start with gear box gear /intermediate gear correlation. Tighten the intermediate gear screw and test operation by turning the intermediate gear wheel back and forth over the whole adjustment range, operation should be totally smooth in both directions, if not, open screw and readjust intermediate gear away from or towards the gearbox gear, tighten the screw and test again.
When satisfied add the fine setting knob, tighten its screw and test for intermediate gear/fine setting knob gear interoperation. Again it should be totally smooth in both directions with no extra sounds. For adjustment you will have to remove the fine setting knob and loosen the intermediate gear screw only this time, you keep the distance to the gear box gear and just slightly move the intermediate gear towards or away from the fine tuning knob gear but keeping the distance to the gearbox gear.
After each adjustment first test operation without fine tuning knob than with fine tuning knob in place. Adjusting is a skill but the learning curve is steep and result very satisfactory. Don’t accept any hanging or rattling , when at a sight honing in the last few critical minutes of a celestial bodys angle any hickups are annoying.

Put back the handle routing the lamp wires off the gears. If you earlier had the handle off without noting that the rear screw is slighly shorter than there is a 66.7% possibility of another fault. One of the too long screws will push the rail for the degree window mask out of its position and the rail end will act as a brake on the degree wheel .( but on your description I don’t think that was what happened).

Rolf Vainio

( The screw heads are instrument versions with narrow slots, spend some time honing and lapping your screwdrivers to exact fit before attacking the sextant, you will be opening and tightening the same screws a lot of times)
( Most threads are in 70 year+ old aluminum watch torques don’t grab the screw driver with you fist, use fingertips )

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