these movements are very similar - the 1120 is the earlier version of the 'Jet' Autodater using the circular geared automatic rotor, first made in 1962. I would guess they are essentially the same movement, with the 4100 being a later development first produced in 1964, with the main difference being that this one added a day wheel. The 1120 is date only (or no day or date) - this is evident from the greater depth of the 4100 movement (6.39mm) whilst the 1120 was 5.00mm. Both are 29mm wide.
The 4100 also had a different range of jeweling - it was 19,25 or 35, whilst the 1120 was 17, 21, 23, 25, 27 or 35 jewels.
The other difference is in dial logos - the 4100 is called the Autodater 'Seven', so you'll find a 7 logo or the word 'seven' on the dial, often also engraved on the case back. The 1120 is the 'Jet' autodater, with the word on the dial as well the Jet logo, also repeated on the caseback:
This pic shows the usual '7' logo on a 4121 ('Monthly') version of the 4100 series:
You can find a movement table I've compiled for the vintage Citizens if you are interested in this brand here:
According to Hampel (the author of two great books about automatic watches) the 41xx bears the same basic movement as the 11xx. He states the main difference being in the way the rotor is attached (and of course the additional day function - btw. only the 1160/61 & 70 have a quickset, where all the 41xx have one)
If you look at the pictures in the book you can see that the 11xx series uses 3 additional parts to clamp on the rotor (and then fix it to the movement with 3 srews) where the 41xx has those plates integrated in the rotor by having them on a ring).
Here's a pic of my 1121:
Great, if you look closely, you can see the difference. The 3 plates that allows to mount the rotor on the movement (and act actually as the rotor bearing are single parts on the 11xx.
On the 41xx they are partof a ring (you can see it just behind the teeth of the rotor gear.
P.S. I replied your PM Stephen
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