A couple of years ago my daughter gave me a Horolovar guide as a Christmas gift. Any horologist will agree that the Horolovar guide is indispensable when working with 400-day clocks.
It is not a manual one opens up regularly but when working on 400-day or anniversary clocks, as they are often called, it is an absolute necessity.
The guide was last published in June of 1991 and I doubt much has changed since then because I know of no mechanical anniversary clocks that are still in production today.
Putting the manual to use
My daughter was in the process of moving across the country. She was unaware of the locking mechanism for the 400-day clock she received as a gift some years ago. Upon unpacking the clock she discovered that the suspension spring had snapped. A snapped suspension spring is not something that can be reused but it can be easily replaced.
400-day clocks require very specific suspension springs, ones specially designed for each of the many dozens of manufacturers in the past 100 years. Install a suspension spring with an incorrect thickness and length and you are asking for trouble. The correct spring for the make and model of clock will ensure a smooth running anniversary clock that will operate for many years.
On the positive side, these clocks run so slowly at 8 beats per minute that is is rare to have worn pivots and bushing holes.
Back to the clock in question. It is a Kundo anniversary clock made in the 1950s. According to the Horolovar guide, it is model 1371. Model 1371 tells me that the thickness of the suspension spring is .081 mm or .0032″. I have worked on similar models in the past and had left over Horolovar suspension springs of that size.
This is basically a one-hour job. There are two blocks, a bottom, and a top. Making sure the spring is not bent during the process, unscrew the blocks (those little screws can be stubborn to move) then insert the suspension spring and tighten the screws. Once the blocks are secure, the manual shows where to anchor the suspension fork.
Install the assembly onto the clock by attaching the top block with a screw that threads into a hole and hooking the bottom block onto the pendulum but your work is not finished.
Now comes adjusting the beat and regulating the clock. There is a bracket above the suspension spring assembly that can be turned (it is a friction fit) in either direction to correct the beat. I set the beat by ear and eye but there is a beat setting tool that can be purchased from a clock supplier if you plan to work on a lot of these clocks. In any event, a beat amplifier is an absolute must.
Most 400 day clocks run at 8 beats per minute. Mine is a little fast at 9 beats per minute but can be adjusted using the dial type speed regulator located at the top of the four weights. One might think that a clock that runs slightly fast may not make much difference but compounded over the course of a year the clock can be fast by many minutes or hours. As anyone who has worked on these can tell you, they are poor timekeepers.
Can you install a new suspension spring without the Horolovar guide? Yes, but you would have to research the suspension spring thickness for that particular model and use the old assembly as a template.
Just buy the guide! It takes all the guesswork away.
Antique and Vintage Clocks 
My Kundo runs too fast with a new .0032 spring and the speed regulator maxed out. May I use a weaker spring to adjust and is a weaker spring larger or small (.0030 or .0035)?
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Hi and thanks for your comment. If you have a Kundo Standard which is the taller one, the correct spring is .0032″. If you have a smaller version of a Kundo, the Junior, the spring is .0023″. If you used the correct spring and maintained the exact distance between the upper and lower blocks your clock should more or less keep decent time. So, if the suspension spring is the exact length and thickness and your clock runs too fast, is it in beat? It should run at 8 beats per minute. To put the clock in beat, ensure that the pendulum overswing in both directions is equal. A healthy rotation should be 270 degrees or more of swing.
I find that it is very important to have the Horolovar manual particularly if you plan to work on more than one 400 day clock. The manual contains exact suspension spring templates for each 400-day clock in production for the past 100 years.
Having said all that, 400-day clocks are terrible timekeepers and if you can get yours to within 5 (plus or minus) minutes per week you are doing well. In addition, most of the mainspring’s power is released when fully wound. The clock will slow down as the mainspring unwinds and therefore will run slower.
Check this out first before you experiment with a thinner spring.
Hope this helps.
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Thanks for your quick response. I have several Anniversary clocks and made it a hobbie to restore them. The “Horolovar 400 Day Clock Repair Guide” is a staple and couldn’t do any repairs without it. FYI- I have completed all the usual as you suggested and hence prompted my contact. I’m really at a lose with this unit. Next I’ll try a stronger suspension spring.
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Not a thicker spring but a thinner one. The “rule of thumb” is that a 0.0001 inch change in spring thickness will give you 4 minutes per hour of rate change. A thicker spring will speed up the clock, a thinner one will slow it down. You could also have fluttering and if so, resetting the forks (straighter and higher) will have an effect.
Ron
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Ron: One last question please. Went down to .0025 suspension spring but now have fluttering. What causes this and how do I rectify.
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Sometimes the anchor bounces enough for an escape wheel tooth to leave the locking face and momentarily touch the impulse face. Too much bounce can lead to loss of impulse or fluttering. Typically, the guide is the “suggested” location of the fork, but you should try moving the fork up the suspension spring towards the top block no more than 2 millimeters or so. Beyond that, I don’t know much more I can suggest.
Ron
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