The sonora chime by Seth Thomas that has dual chimes (whittington and westminster ) has 2 small dials about 1 inch in diameter on the top of the face. One of them is for the chime selection and the other is for the timekeeping adjustment. The mainspring in the chime unit is larger than in the single chime unit; it's dimensions are: strength: .0215inches thick by 1.375 inches wide by approximately 106 inches long.Be careful with this spring. When it is wound fully it has a lot of energy stored in it. If you are installing this with a spring winder, I would strongly recommend wearing a face shield; not just eye protection, but a face shield and eye protection. The sequence of the hammers is as follows: looking in the back of the case assign numbers to the hammers and let the hammer closest to the back be #1 . The wittington sequence is as follows at the quarter hour chime: 1, 4, 6, 7, 2 ,3 ,5 ,8. The westminster chime at the quarter hour is: 6, 7 ,2 ,8.This clock has two mechanisms. The one closest to the front of the clock powers the strike and the time gear trains. It also trips the chime. The chime mechanism is closest to the back of the clock. The chime mechanism has a huge mainspring and mainspring barrell. Pay very close attention to the teeth on this barrell; if this mainspring or barrell lets go , it will do much damage to the mechanism and possibly to someone's finger.
Most of these clocks are not self correcting on the chime or the strike.The mechanism that runs the strike and the time is very similar to the 8 day time and strike american clock mechanisms. The chime usually is sounded on a row of bells mounted above a resonating box. These clocks have a beautiful sound in my opinion. The hammer sequence is different on these clocks than on the modern german w/c self correcting mechanisms. The time and strike mechanism is activated by the chime mechanism, however, the chime mechanism is activated by the trip lever and the trip cam in the time and strike mechanism. It is a good idea to be very sure you have the lift wires correctly adjusted before you re-install the mechanisms in the case. I have usually set them up on a couple of blocks outside of the case to get the adjustment reasonably close before installing the mechanisms. Be absolutely sure to check the ratchet dog system on the chime mechanism; I have seen many of these loose when they come in for repair. If one of these lets go, the results will be disastrous indeed. The mainspring in one of these mechanisms is powerful enough to easily break someone's finger. There is usually a pin on the inside of the ratchet that the click spring pushes on to make the click work. Be sure to check this pin very carefully, it must not be loose or the ratchet system will fail. The pendulum on these mechanisms usually will have at lease 2 inches of swing, and the pendulum bob is one of the heavier (2+ ounces typically) types. Before getting too far on the repair of one of these clocks . it is very wise to check the gear teeth on the chime mainspring barrell. If the barrell is bad , there is no point in doing the rest of the work until the barrell problem can be resolved. If the chime mechanism won't work, then neither will the strike . The hammer throw is critical on these clocks ; it may have to be reduced if it has been tampered with. Take the hammer assembly out, take it apart and clean it throughly. If you do not do this you will be insulting the integrity of the owner and the quality of the clock. I have frequently seen these mechanisms bind up because of excessive hammer friction due to too much throw or gummy oil. Unless you are working on a family heirloom, be prepared to have trouble with these clocks. Not that they are bad; on the contrary, they are excellent clocks in my opinion. Many of them I have seen have been butchered, or have had so much oil slopped on the gears that the chime mainspring barrell has teeth that are dangerously worn. You can save yourself a lot of headache and embarrassment by checking the chime mainspring barrell while the customer is there, if possible. If you have too many customers to check it at the counter, be sure to check it BEFORE you get into the repair. Look at the teeth on this barrell carefully. If you see grooves worn in the teeth be alerted. It has been my experience that more than 10% wear on these teeth will cause the chime to bind up sometimes. I have seen them with more wear that will still make the chime work. This is an extremely dangerous situation. Here we have a situation of what you can get by with, and what is a good restoration. The damage has already been done. Now the owner has to decide if they want to keep the original barrell and risk destroying the rest of the clock by running it until the thing explodes, or not running it and having it original. It is a judgement call as far as the antique condition of the clock is concerned. The hammer sequence on the single melody westminister chime is different than usual. It is as follows: looking in the back of the clock and assigning numbers to the four bells used for the quarter hour melody starting with the bell closest to the back door and calling it #1 and the one next to it #2 ,Then #3 and finally #4 , not counting the bell used for the hour strike or course , the order for the quarter hour chime (down the scale westminster) is ; 2 ,4 ,1 ,3 . This same sequence would also apply to the 3rd measure of the 3/4 hour chime.