The nice thing about a battery-operated clock movement is that you're free to put the clock virtually anywhere with no electrical outlet necessary. The downside is that besides having to replace the batteries from time to time, parts of the clock movement might bend if the clock falls off a wall and the clock comes apart. Replacing the clock movement is fairly simple, but it's important that the new movement has the same shaft size as the old, or it may not fit properly in the clock.
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Remove the Old Movement
Before installing or even purchasing the new clock movement, the clock needs to be taken apart to make sure you get the right-size replacement part. Since all clocks are assembled differently, this means examining it up close to figure out how to remove the glass or plastic cover that protects the clock face. In some cases, it simply pops off with a little prying; in other cases, spring clips on the back hold the clock's framework together.
Remove the clock hands one by one to access the nut holding the clock movement to the clock face. The minute hand sometimes pops right off with a little wiggling; in other cases, there may be a tiny cap or nut to remove first using needle-nose pliers. The hour hand comes off with some wiggling. Measure the length of the clock hands, as those that are longer than 9 inches or so usually require a high-torque replacement clock movement. Once the hands are off, remove the nut around the shaft by turning it clockwise with a small wrench or needle-nose pliers.
Pull the clock movement off the clock and measure the threaded part of the shaft on the clock movement. Don't measure the other part sticking out beyond the shaft. If there's something unusual about the size or the shape of the old clock movement, note those measurements and details as well. Some battery-operated movements power a lightweight pendulum, for example, so it's important to buy the same type to ensure your clock works after replacing the part. Replacement models either have hands that tick as they move, called step movements, or those that move continuously, called sweeping movements, so be sure to buy the type you prefer.
Install the New Movement
Installing the new clock movement is the same as taking the old one apart but in reverse. If the new movement has the nut and hands installed, take those off first as you did on the old movement. Push the shaft of the new movement through the back of the clock and then place and tighten the nut over the shaft by turning it clockwise with a small wrench. Push the hour hand in place and then the second hand as well as any nuts or caps used to secure the second hand.
Test the clock movement before replacing the clear glass or plastic shield that protects the clock face. Insert fresh batteries of the appropriate size into the clock movement. Set the correct time on it by moving the minute hand clockwise; the hour hand should follow, but if not, rotate it as well. Wait five minutes or so; if the clock is working properly, the minute hand shows the current correct time. Once you're sure everything is in working order, place the protective dome and/or bezel around the clock face and set the clock in the desired location.