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.