Advice after first service - 8-day aircraft clock

br1anh · February 2

I recently finished my first full disassembly and cleaning of a movement. It is a Lemania 7-jewel movement from an 8-day aircraft clock. I started with this one because I had the clock on hand and wanted to get it running for use in a small desktop enclosure. It would only run when given a shake or when you slowly advanced the hands when setting, so I hoped it was just in need of a good cleaning. The main plate is about 45mm, so it is kind of like a jumbo pocket watch. The barrel and first and second wheels were pretty stuck, so that seemed to be the cause of the non-running. After cleaning in naphtha and 99% alcohol and several rounds of pegging bushings, I reassembled and lubricated the movement. I had a few beginner challenges along the way (the shock settings in particular), but got it back together and running. So I guess that is a win -- it went from not running to running.

The functional test listed in the maintenance manual isn't very rigorous -- observe the movement for 4 days, make sure the daily rate doesn't exceed 30s/day, and that it doesn't vary by more than 15s from the average rate for any day. It also needs to run for at least 8-days. I haven't made it to the end of 8 days yet, but it is still running after 5, and the error for the first four days were within a second or two of +30sec, so I think with a slight adjustment to the regulator it will easily satisfy that test. However, the amplitude dial down is about 230-240 degrees, and in the 12 up position (the primary position for this clock) amplitude drops to 170-180 and gains 10-15 seconds in rate.

My questions are:

1. What kind of amplitude should I expect from this 7-jewel 8-day movement? Should it be similar to the typical recommendation? More like 270+ horizontal and 220+ vertical?

2. If I should expect more amplitude, where should I look to evaluate the movement and/or my cleaning/lubrication procedure? The balance pivots/jewels? One end or the other of the train? I could re clean the entire movement, but I'm thinking it would be more instructive to make targeted changes to see what has an effect on performance.

3. The metal bushings took quite a bit of rubbing with pegwood to remove the sheen/residue of old lubrication. I'm not sure I was able to clean inside the holes as well as I was the surfaces. Is there any other recommendation for cleaning inside the holes? Perhaps a cleaning machine with cleaning solutions or an ultrasonic would have been better, but I haven't progressed to that equipment.

Thanks in advance for any advice or recommendations!

Yani365 · February 8

I'm a beginner too, but I would expect that if the balance is losing amplitude when the pivots are parallel to the ground, then there is likely some added friction in that position. As you suspected.

A movement this age, I'm guessing mid to late 1960's, may have some wear on the pinions in the jewels or bushings, and they may still be dirty. I would try soaking the jewels/bushings in naphtha (Zippo lighter fluid) and then take a close look for any dirt. Also, the pinions may be worn or damaged. Try using a 10x or more loupe to really see what's up. More than likely its dry oil.

Also, are you lubricating the pivots for the balance wheel? If not, that's absolutely going to effect amplitude on the balance, and will reduce power transfer in the train.

Let us know how its going!

br1anh · February 10

Yes, I lubricated the balance pivots, and they show a decent circle of oil under magnification. The movement ran for over 9-1/2 days with a consistent rate through the first 7, so I'm assuming the mainspring is adequate.

My next plan is to slowly work back from the balance end of the train. First seeing if a careful cleaning of the balance pivots and jewels makes any difference, then moving on to the center seconds pivots until I end up recleaning and polishing all of the metal bearings. I know I had better luck cleaning the bearing faces than inside the pivot holes, so will try a soak with more determined pegwood cleaning, perhaps with a bit of red rouge.

I also noticed that the last person in here seems to have tweaked the hairspring stud along with the end curve -- notice in the photo that the stud is not sitting with the flat against the set screw. The hairspring is a bit off center. I expect this would be more likely to affect positional rates than amplitude. It appears intentional, but I'm not sure what they were trying to achieve. I'm going to leave it for now, as I still need more hairspring practice and it is running pretty well.