How To Build And Install A Suspension Unit
Of all the things that can go wrong with an anniversary clock, by far the most likely is damage to the delicate suspension spring. The spring can break, or become bent or kinked, usually due to mishandling of the clock. (Steel or bronze springs, which were originally fitted to many clocks, are relatively brittle, and more prone to breakage even under normal use). Often, when the spring breaks, the bottom block (the brass piece at the bottom of the spring that holds the pendulum) becomes lost and must also be replaced. There are a couple of dozen different thicknesses of suspension spring that the manufacturers used, and well over 50 different suspension unit configurations, with just as many varieties of blocks and forks. How do you know what thickness of spring your anniversary clock requires? A spring that is too thick will cause a clock to run fast, even at it’s slowest setting. Conversely, a spring that is too thin will cause a clock to run slow, even at it’s fastest setting. Trying to match your old spring is not a good idea. It is difficult to accurately measure down to the nearest 10,000th of an inch (.0001"), even with a very good micrometer. Even if you could, the old spring would also have to be Horolovar, or it's performance characteristics would not be the same. How do you know which blocks and forks will work on your anniversary clock? The shape of the blocks are not critical, but the thickness is. For the fork, the distance between the two tines is most critical. With some careful measuring and a little math, you can figure out how long the suspension unit needs to be, but how do you know where to locate the fork? If the fork is still attached to the old spring, you have a good starting point, but mount it too high, and the clock won't run; mount it too low, and the clock flutters. Until Charles Terwilliger, the founder of Horolovar came along, finding all this out was a matter of trial and error. Clock repair people had good reason to hate working on anniversary clocks! In addition to developing a temperature compensating suspension spring, Charles took the time to test and document pretty much every different make and model of post WWII anniversary clock ever produced, as well as most pre WWII clock makes and models. He documented his results in The Horolovar 400 Day Clock Repair Guide. Now in the 10th edition, it is the most accurate and complete reference available. With it, you can compare your clock’s back plate with those in the book to find who made the clock, approximately when it was first made, what size mainspring and suspension spring the clock requires, and for the post WWII clocks, a drawn to scale diagram of the clock’s suspension unit, with the fork located in the optimal operating position. If you plan to work on many anniversary clocks, I highly recommend you obtain a copy. If you only plan to fix the one you have, send us a close up picture of the clock’s back plate and pendulum, and we’ll be happy to look up the information you need to find the right springs, blocks, or complete suspension unit. We’ll assume from this point on that you have the parts and information specific to your clock’s suspension unit.
Smaller size flat head screwdriver
Precision flat head screwdrivers
Horolovar beat setting tool (long handled pliers will work instead)
Long handled pliers
Needle nose pliers
Scissors or toenail clippers
Additional helpful items:
Strips of cardboard or a Styrofoam block
Toothpick or taper pin
Small box or ice cube tray
If you have trouble seeing small things, a magnifying glass will also prove helpful.
Make or otherwise obtain a copy of your suspension unit illustration for use as a template. Tape it to couple of pieces of cardboard layered on top of each other, or a chunk of Styrofoam. These materials will provide support, while allowing the bottom block to lie flat.
Follow these tips to help prevent ugly scars on the screw heads, and make your work look more professional. Remember Dad’s old saying, ‘Lefty loosey, righty tighty’. Turn the screwdriver counter clockwise to loosen a screw, clockwise to tighten it. Always select the largest screwdriver you have that will fit the slot in the screw. When initially loosening a screw, apply more force directly down on the screw than you apply to loosen it. Do not over tighten a screw. There is no need to torque it down with all your strength. Unless directed otherwise, just a few pounds of torque is all that is necessary.
Clear a work area. You’ll need a chair, a steady table, and good lighting. Designate a handy, out of your way spot for your tools, and another for clock parts. I find it works well to use a small box or an ice cube tray to set your small clock parts. They are easier to see, and it prevents them from rolling off the table. Place the clock in front of you, with the back of the clock facing you. Remove the dome, and place it in a safe spot.
The first thing to do is remove the old suspension unit. If you have a Kundo clock with a pendulum locking device, chances are the bottom block is still inside the pendulum, even if the old spring broke. (If the old spring is intact, you’ll find it easier to remove the pin with the pendulum locked in place, or you could just cut the spring.) Depending on when your clock was made, the old block will be held in place by either a cotter pin, or a thick straight pin. If it’s a cotter pin, use your needle nose pliers first to straighten the ends a bit, then to pull it out by the rounded end. If it’s a straight pin, grasp one end with your needle nose pliers and pull it out. If it is stubborn, use a twisting motion while you pull. Once the pin is off, the bottom block will slide out of the slot in the pendulum. For any other kind of clock, just lift the pendulum straight up about ¼” or so, and push the suspension spring toward the open end of the pendulum hook.
Remove the suspension spring guard (if present). If your guard is plastic, and it is not attached by screws, place a finger and thumb on the sides of the unit over the top tabs, then gently squeeze and pull back until the hooks are released. Repeat over the bottom tabs. If the guard is held in place by small guard holding screws (they may be located inside two holes on the back of the guard), one full turn of the precision screwdriver is enough to loosen them sufficiently to be able to remove the guard. After loosening the screws, lift the guard up slightly, then pull back directly away from the plate.
Disconnect the top block by unscrewing the suspension unit holding screw all the way off. You should be able to do this by hand, but it could be screwed in much more tightly than necessary. If so, loosen the screw using your pliers, taking care to turn counter clockwise to avoid the potential of breaking off the threaded end of the screw in the saddle, requiring both pieces to be replaced. Koma clocks use a taper pin instead of a screw. Just pull the pin out by the thicker end. Grasp the fork where it meets the spring, and pull the unit straight back.
Now that the old suspension unit is out of the way, let’s perform a test to ensure that at least some mainspring power is reaching the escape wheel, and that the escapement is in good repair. Make sure the clock is at least partially wound. Turn the clock so the left side is facing you, and you have a view of the front of the back plate. Place a finger on the anchor shaft (the anchor is the top-most gear) , then slowly and gently rock it back and forth. You should notice two things: 1) the escape wheel (the gear under the anchor) should advance counter clockwise one tooth at a time with each motion of your finger, and 2) the minute hand should also advance (clockwise) with each motion. To thoroughly test all 15 to 20 teeth in the escape wheel, count by one for each combined back and forth motion (back and forth, one, back and forth, two...) until you count to 20. If the escape wheel advances each time, and you see the minute hand advance, your clock has passed the test. If not, your clock requires additional servicing, and will not run just by replacing the suspension unit.
Your Horolovar suspension spring is flexible, strong, and durable. But it will not tolerate abuse. It can easily develop a permanent crease, especially between the top block and fork. It will kink if twisted too far. Handle it with care. Care must also be taken when handling the fork. Inspect it carefully. The two tines should be parallel to each other. If they get pinched together, or pulled apart, your clock will not run. The distance between the two tines should be such that when in place over the anchor pin which is in a vertical position, a single sheet of paper should fit on one side. If the fork appears damaged, it should be replaced.
Equally important as the correct thickness of spring, the pendulum must be correct for the clock, and in good condition. If it’s too heavy, too light, too tall, or too short, your clock will not keep good time, and may not run at all. Check the pendulums in section 13 of the Horolovar guide if you have any doubt. If the pendulum has been dropped or otherwise abused, it’s weight may not be evenly distributed, causing it to wobble. Check it for misalignment or other visible damage.
If you want to play around with a suspension spring to see what you can do to it before it creases or breaks, here’s your chance to do so without ruining a good one. Provided it is not already twisted all the way up the spring (as happens when someone twirls the pendulum as hard as they can), you can get a fairly good idea of what you can do, and what you can’t. I say fairly good, because the old spring may not be Horolovar, which is a special alloy. Steel and bronze springs were commonly used in the past. In addition to their poor performance in the face of variations in temperature, both materials are more brittle, which causes them to break easier.
Remove the screws from the blocks. Steady the piece by gripping the edges with your needle nose pliers, while the block is resting on the table. To help avoid damaging the slots in the screws, select the largest screwdriver you have that will fit into the slot, and use at least as much downward force as lateral force when loosening each screw. Put the screws in your box or ice cube tray so they don’t get lost, and keep them together with the block they were removed from. Inspect both inner surfaces of each block for a broken piece of spring, even if the old spring did not break. A piece may be there from an earlier repair, and its presence will impair the block’s ability to hold the new spring securely. Do not grip the fork by the tines. If it has only one screw, just loosen it. If it has two screws, loosen one and remove the other. Slide the fork off the old spring.
Now you are ready to assemble your new suspension unit. Position a suspension spring over the picture of the spring on the template, so that one end starts just below the hole in the top block. Now lay the sticky end of a post-it-note over the spring, lining the edge just above the picture of the pin in the bottom block. This marks where the spring will be cut. The idea is to make the spring as long as possible, to provide maximum material for the blocks to grip. As a bonus, if the spring later happens to bend or break just past one of the blocks, what’s left of the spring may be long enough to reuse. Carefully pry up the post-it-note; the spring should come up with it. Cut the end of the spring even with the post-it-note using a pair of sharp scissors or toenail clippers. Remove the post-it-note, and check the spring against the template to make sure it is the right length. Reapply the post-it-note over the spring, with the sticky end running perpendicular to the middle of the spring, and the non-sticky end toward the illustration of the bottom block.
I prefer to attach the top block first. Stack the two halves on the table over a napkin, hold them steady with your needle nose pliers, and screw in the screws just enough to catch on the lower half of the block. If you have problems manipulating the tiny screws with your fingers, tweezers or a toothpick may help. If you use tweezers, be very careful not to squeeze too hard. The screw could go flying who knows where, and it’s no fun searching the floor to recover it. Insert a toothpick or pin under the suspension spring toward the illustration of the top block to lift the spring up slightly. Make sure the top block is oriented correctly, then, using your needle nose pliers, grip the side edges of the top half of the block, and slide the spring into the gap between the two halves of the block. This may take a few tries, just be patient. Once inside, line up the block with the illustration, stick a taper pin or toothpick through the hole in the top block, and continue to hold the block in place with your pliers. Make sure the spring is exactly centered in the block. Screw in the screws very firmly, but don’t use too much force, or you may slip and crease the spring. Remove the post-it-note, and make sure the spring is still centered, and the right length. The process is nearly the same with the bottom block, except you will set the block on cardboard or Styrofoam to allow it to lay flat when loosely screwing in the screws, and you will reverse the position of the post-it-note before sliding the block on the spring. Leave the taper pin or toothpick in place to keep the top block from flopping around. Once the bottom block is secured, attach the fork. Using a toothpick to lift the spring, slide the fork over the spring, and line it up with the illustration. Again, be careful when gripping the fork, and when tightening the screw(s). When you finish, again compare your unit with the template to be sure everything matches. Give a little tug on the top and bottom block, then the fork, to ensure everything is securely fastened.
You are finally ready to install the new suspension unit! Grasp the suspension unit by the fork where the spring runs through it. With your free hand, use your finger on the anchor shaft to position the anchor pin vertically. Line up the top block with the slot in the saddle and insert it part way. Now capture the anchor pin between the fork tines, then move the suspension unit forward until the top block is centered in the saddle. Retrieve the suspension unit holding screw (or taper pin). Lift the top block up just a bit within the saddle to help line up the hole in the top block with the hole running through the saddle. (When it is lined up properly, you can see straight through.) Insert the screw (or taper pin) into the larger hole in the saddle (the same one it came out of), and push until the screw goes through the hole in the top block. This may take a little manipulating with the top block, just be patient. Once the screw has gone through the hole, screw it in by hand, finger tight. The top block should be able to swing forward and backward freely. Test for forward and backward motion by using your finger to push softly on the back of the fork.
If your clock does not have a suspension guard, all that is left is to hang the pendulum. If it does have a guard, now is as good a time as any to reattach it. The hardest are the brass tube variety that have the guard holding screws located down the center of the back plate. With the bottom of the guard unit at an angle away from the clock, slide the guard unit up over the bottom block, and slowly lift until the bottom block emerges from the bottom of the tube. If the block gets caught, lower the tube slightly, turn it a little, and lift again. (You may also need to spread the little pincers on the lower guard apart.) Once the bottom block emerges, rotate the guard so the 2 small holes for the guard holding screws face the back plate. Make sure the fork tines are still straddling the anchor pin before continuing. Line up the holes with the guard holding screws, and hang the unit on the screws. Before tightening the screws, hang the pendulum on the bottom block, with the bottom of the pendulum inside the guide cup. The weight of the pendulum acts to hold the suspension spring taught in the middle of the tube, reducing the likelihood of trapping the spring behind the head of a guard holding screw, which, after you tighten the screw, will ruin it. (Been there, done that.) Once you’ve hung the pendulum, use one hand to lift up on the bottom of the guard unit, then carefully tighten both screws. If your guard has them, return the pincers to the correct position. Remove the pendulum, loosen the guard locking thumb screw ½ turn or so, and lower the bottom suspension block guard until it is close to the bottom block. The pincers are in the correct position when they are close enough together that the outer extreme of the pin running through the bottom block rests within the ’V’ of the pincer (this is the proper position for the guard when transporting the clock - with the thumb screw tightened). You don’t want them any closer together than they have to be, as they may rub against the spring when the pendulum wobbles. Once accomplished, raise the bottom suspension block guard as far as it will go, and tighten the thumb screw.
If you have a Kundo clock with a pendulum locking device, here’s how you hang the pendulum: Lower the bottom block into the slot at the top of the pendulum, then lock the pendulum in place. Turn the pendulum so the hole in the side is facing you. If your bottom block was originally held in place by a cotter pin, reinstall the cotter pin. Straighten the cotter pin as well as you can, then reinsert the pin into the small hole, through the hole in the bottom block, and out the other side. (Can be easier said than done.) Then use your needle nose pliers to open the ends again, to secure it in place. The rest of you with newer Kundo clocks will notice a thin ring on the neck of the pendulum, which is held above the round hole by a spring. The bottom block should be resting within the hole. Push the ring down even with the bottom of the hole, and hold it in place with one hand, keeping your fingers away from the hole. Using your needle nose pliers, grasp one end of the pin securely, and push it through the hole in the bottom block. The ends of the pin should stick out evenly on both sides. Let go of the ring. It will push up against the pin, acting to hold it in place while transporting your clock. Carefully release the pendulum from the locking device by letting the pendulum down gently with your hand rather than letting it drop on it’s own.