back side of Spilhaus Clock

How to Repair a Spilhaus Clock

Removing the Works

Instructions for removing the works:

  1. unplug the clock
  2. remove the back by prying at the sides. Never pry from the bottom as it pushes in the top against the discs.
  3. remove the metal strap that holds the power cord to the bottom of the case (see B above)
  4. unscrew the wood L bracket from the bottom of the case (see A). It is not necessary to remove the L bracket from the works of the clock.
  5. remove the magnets that hold the back to the case on either side (see C)
  6. remove the two screws that hold the clock to an internal bracket (see D) Note these screws are different from the previously loosened wood screws and they generally have round heads.
  7. tilt the top of the clock out first as this raises the bottom of the two bottom dials out of a depression in the bottom of the case. (The depressions are behind the labels for A and B. It helps to hold the dial side of the clock up, and the back of the clock down, and let the works fall gently into your lap.)  Sometimes there is a gray plastic guide at the top of the arch and it serves to keep the discs separated.  This is sometimes, incorrectly, attached to the top of the arch.  It will need to be pried apart so the top of the discs can come out of the cabinet first.

Clock Repair

Because of this article, I have received numerous inquiries about fixing the Spilhaus Space Clock.  I no longer fix these clocks.  However I am happy to describe the work and even consult with a clock repair person about your clock. Repairing the clock does not take much knowledge and requires only a moderate understanding of mechanical things.  No special tools are required beyond a screwdriver, hex wrenches, and some dish soap to clean the insides.

I spent several years looking for a machinist willing to make the replacement gears. The gears are made out of Delrin, a more stable plastic, and will not shrink. Delrin is a more permanent fix. The gears should not be made out of metal as they will gall the soft plastic teeth on the outside of the discs.  Some clocks have metal gears, including one or many.  While the metal gears will wear the plastic faster, the wear is negligible and it is expensive to replace all the gears with Delrin.

I am no longer able to supply lamps.  Please see my comments below.  I suggest it is possible to convert your clock to use different lamps such as the common 44 or 47 bayonet mount lamps.  I have not done this yet but have tried the sockets to see if they will fit.  There are also some new LED lamps in the telephone slide configuration.  These may work but the clock will have to be rewired so the bulbs are in parallel and the light provided will be very different.

My clock was missing the circular diffraction grating.  I was able to find a similar diffraction material in stamp kits for children however the pattern was flakes rather than a circle.  Guido Santacana of the US Commonwealth of Puerto Rico was able to find out more information about the original material:

"(The circular diffraction gratings) were manufactured by or for Edmund Scientific as part of their exclusive diffraction jewelry that went by the name of Jewelarama back in the 60s. Search google under this trademark and you will find a lot of jewelry with the diffraction discs that can be easily removed. They seem to have used the same discs in the Spilhaus. Another thing is that the 1" disc seems too big for the sun. The original sun disc was about the size of a penny or about 3/4" as you correctly estimated. This size fits perfectly the empty space where the sun disc is supposed to be."

Spilhaus Clock Gears

How to Examine Your Gears

The clock may appear to be working. The small 12 hour dial will keep the correct time and the other display dials may continue to turn. Unless you keep accurate track of the moon and sun position, the tides and the date, you will not notice that anything is amiss. With a cracked gear, all the functions will continue to turn but will be rotating at a slower rate, adding errors to the display. The gap in the gear, where the split occurs, will act like an extra tooth as the display discs rotate.

Unfortunately it is very common for the gears to split. Eight out of ten clocks will have at least two split gears. The left arrow points to the most common position of split gears. Occasionally you will find the next gear over, the yellow arrow on the right, will also suffer from a split. More rare are splits on the two sets of gears on the right. I have seen one unfortunate clock that has all the gears split or starting to split.

In order to check the gears without removing the works, try the following. Examine the gears by looking carefully from the front, at the bottom left part of the big dial, around the number 22. You are looking in the main dial, just above the 12 hour clock. Look down into the works and look for the small gears.

Turn the blue knob or the brass metal knob used to set the time and watch the gears rotate. The split will look almost like a missing tooth (see below). You can turn the blue knob to to check the gears to the right of the small gears. Again, see the yellow arrows above for the position of the larger gears. You can rotate the gears in order to examine them completely.

It will not be possible to see all the cracks or even the beginning of a split gear. The only way to be certain that the gears are whole is to remove the works from the case and examine the individual gears with a magnifying glass. The start of a split appears as a hairline crack, usually radiating outwards and starting near the metal bushing.

To examine the gears more carefully, begin by taking the works out of the case. See the instructions above for the removal. Once the works are removed, the gears will be visible as shown below. Carefully examine the gears for cracks or the starting of a split. You will need a magnifying glass to see if the plastic is solid or not.

gears from the top

This is the view as if you are looking down through the main display dial, at the 22 hour position. The dials have been removed so you can see the gears more clearly.

new parts for the Spilhaus Clock

Replacement Parts

Note the five broken gears above. The right most gear has cracked completely and the parts no longer fit on the bushing. Look carefully at the small gear in the middle. It has been repaired with a small wooden tooth. Unfortunately this changes the gear ratio and the clock will not keep track of the time correctly.

The gear on the bottom is a replacement made from Delrin and includes the center metal bushing.  Metal bushings can also be supplied if they are missing.

Replacement gears can be purchased from Steve Cotton of Micro Precision Parts Manufacturing. You can contact him through the website or by phone, (250) 752 5401. He is located in Qualicum Beach BC on Vancouver Island in Canada.

The original gears were made out of Nylon.  As the plasticizer evaporated, the gear material shrinks.  The Nylon can only shrink so much because of the metal bushing and eventually cracks.  Some of the cracks are difficult to see without careful examination.  Sometimes a flap is across the gap and the gear appears complete when it is not.  Most often the small gears attached to the gold knob crack but I have found every gear is susceptible.

The small and large gears are concentric and have a friction clutch between them. The friction material can be cleaned and reused. A thin rubber, like that used to provide additional grip for opening jars in the kitchen, can be used as a replacement if the original clutch cannot be used.

Occasionally I find a gear has been replaced with a metal duplicate. This should be avoided as the metal will wear the teeth on the discs prematurely, ruining the plastic teeth on the clear indicator discs.  While I have seen clocks with one or two of the Nylon gears replaced with metal, and even a clock with all metal gears, I do not believe these were done originally at the factory.  Because they are not uncommon, the factory may have supplied these for a time as replacements. 

The two lamps on the top are original replacement 48A lamps. Note how the metal goes all the way to the left and the glass is longer than the replacement below. All three will work. I do not recommend the 48C lamp that is commonly referenced as a replacement. It uses half the current and is half as bright. Look at the picture of the lit clock at the bottom and you will see the light provided by the 48A lamps is a warm glow.

I am no longer able to source for the 48A lamps.  Many lamp stores incorrectly cross reference the 48A lamp with the 48C lamp.  The 48C are half as bright and do not provide sufficient light to see the dials. For this reason I do not suggest using the 48C lamp. 

Beware of off-brand replacement 48A lamps as they may be very poor reproductions and will not work correctly.  Be careful and specify the correct lamp and that you want a C5 filament.  Some of the cross referenced bulbs do not provide the correct configuration.  When in doubt, visit Don's Bulbs to find the correct configuration.  Please let me know if you find a reliable source for Sylvania or GE 48A or 48A-2 lamps and I will pay you a finder's fee.  See my story about why you should avoid Atlanta Bulbs.  They cannot supply the correct bulb and are dishonest.

The lamps are wired in series. When one lamp burns out, all the lamps stop working. You can test the lamps to see which one is bad and only replace the burned out lamp.

Brass Polishing

The bezel and arch over the top are made of brass and tend to discolor with age. This is normal and adds to the patina of an old object. Unfortunately in a moist environment, near the ocean for example, the brass will corrode so badly it will appear a dull, muddy brown. It is possible to shine up the brass using a buffing wheel.

The brass can be left to develop a new patina however finger prints will accelerate the corrosion.  There are two ways to protect the new, shiny brass.  I prefer to wax the brass but this requires an occasional wax coat as preventative maintenance. Or I use an oil based clear coat to avoid additional corrosion. I can do this but prefer not to. The results are variable and may not meet the expectations of the owner.  Polishing is very expensive as I charge by the hour and polishing is labor intensive. Please let me know if you are interested and we can discuss it.


The motor is still available. It is easily replaced. However, there is little to go wrong with it and they rarely fail. They fail by becoming noisy and running hot.

Sun and Moon indicators

The original sun and moon circles, found on their respective discs, often fall off and are lost. The circles are made from circular diffraction gratings. I have not been able to find correct replacements I have been using holographic stickers, as found in kids' sticker rewards packages, to make similar circles. Please let me know if you find a source for small, circular diffraction gratings.

Packaging your Clock

I have shipped several of these clocks and found them to be a challenge. The biggest concern is the curved front dial as I do not know how one might go about replacing it. It is also necessary to keep the display discs from rubbing against each other and thereby reducing their transparency. Here are the steps I take to insure the clock will make the trip.

  1. stabilize the display discs. Open the back of the cabinet and place the original shipping clips, bent pieces of metal, around the circumference of the discs. Often the clips are missing, so you can use folded business cards or folded strips cut from paper plates. The idea is to keep the discs in place and not to let them rub against each other.
  2. close the back of the cabinet and place a piece of cardboard, slightly larger than the back of the clock, against the door. This keeps the pressure of the packing materials from pushing in the rear door.  Make sure the rear door does not push against the clear discs in the top of the arch.
  3. wrap the cabinet and cardboard in two or more layers of bubble wrap.  (If you use packing peanuts or loose foam, enclose the clock in a plastic bag.
  4. place the wrapped clock in a box only large enough for the wrapped clock.
  5. place this first box in a second box that is at least four inches larger in all dimensions, allowing at least two inches of bubble wrap or packing peanuts on all sides.
  6. include your name, address, and contact information inside the box.