Restoration: Cleaning Guide

Antique coin mechanisms are among the dirtiest mechanisms you will find in an old coin operated game. There is something about the oil, dirt and grime that finds its way on to money and from there into the coin slide. Worse, human oil is one of the most corrosive substances known to man. Add old grease or oil, dirty money, and smoke filled rooms and you have a mess!

This article will help you clean almost any part of a coin operated machine. However, some of the cleaning techniques are drastic and can damage the cosmetic parts of the machine. Please be careful and consider which method is least likely to damage parts, use those first, and always test on a hidden portion of the game before proceeding.

The coin slide has characteristics of many of the other mechanisms found in a machine. It is precise, measuring the coin carefully and accepting it only if it is correct. It often is chrome or plated so as to invite the user to play and pay. And it is often intricate, needing to perform several operations with springs and levers and magnets.

So, how do you get a coin mechanism clean? You can use the standard methods or you can try some new and modern methods. I will try and describe both and show the advantages and disadvantages.

Removal and Disassembly

First you need to remove and dismantle the mechanism. There are many tricks on how to record the disassembly in order to insure later assembly. Old technology says to draw pictures as you take it apart. I also lay the pieces out in order in various small boxes. Once cleaned you can reverse the order. If you have two similar mechanisms, you can clean one and use the second as an example, and upon finishing, clean the example next.

A modern method is to point a video camera over your shoulder. Start recording, and dismantle. Then, using your remote, reverse the process. Upon successfully finishing, you can sell the video and recoup your investment in the video camera.

All parts must be disassembled. There can be no inaccessible areas. For example, all axles or slides must be separated. There are exceptions, and reasons give later.

Cleaning Agents

Now the cleaning can start. My favorite cleaner is a regular bathroom cleanser, tooth brush and Q-tips. Good old elbow grease will get most of the dirt off. Tri Sodium Phosphate will also remove a lot of grease. For fragile parts, you can used a good non-grit cleaner used for fiberglass tubs.

Modern methods use new chemicals and devices! Freon was great because it would take off anything and then evaporate, leaving no trace. However it is unfriendly to the environment and no longer available. Automotive carburetor cleaner is great, but contains trichloroethane or other volatile and should only be used according to directions. It does also leave some residue that you must then get off before the parts are truly clean. I only used these as a last resort.

My wife is a mechanical engineer for an aerospace firm. She specifies clean parts for space experiments. The company documents are very specific on getting parts clean. Most of their cleaning procedures start with MEK (methyl-ethyl-ketone) followed by de ionized water rinse. Blow dry with nitrogen! Then comes the ultrasonic cleaner! I compromise with the following. In many cases, one of the steps is an etching, where the part is subjected to a mild acid. It actually removes some of the metal. You can used things like phosphoric acid or hydrofluoric acid as found in Whink Rust Stain Remover. This is too aggressive for me, but it will help remove rust in the corners of the coin box.

Rock Tumblers or Vibrators

There are several mechanical devices that will help the cleaning process. Pull out that old rock tumbler or go to a restaurant supply and find an old dining utensil tumbler. You can also find the more modern version of upright tumbler in scientific supply stores or mail order from Edmund Scientific. The tumbler vibrates or tumbles cutting material against the metal parts you are trying to clean. Some of the cutting materials are more aggressive than others. Utensil tumblers usually contain small metal balls that tumble and polish the silverware. This works well on leg bolts and other metal parts that are not plated.

I use treated corn cobs for fragile plated parts. I do not want to wear off the plating, just remove the corrosion. You can add some Brasso or other polish to the corn cobs to speed the process. Put the slide parts in with the corn cobs and let it go for an hour or so and check the progress.

For more aggressive cleaning, like metal plates, nuts, bolts and springs, I use ceramic material, shaped in a diamond. This cuts quickly so care must be taken not to leave the parts in too long. Add a magnet to the mix and the small parts will collect on the magnet, making them easier to find.

Ultrasonic Tank

My favorite cleaning device is the ultrasonic cleaner. The ultrasonic cleaner is a tank of liquid and a transducer to vibrate the liquid at very high frequency. The liquid vibrates so quickly microscopic bubbles form on the part to be cleaned, and then pop with such force the dirt is blasted off.

There are many different liquids you can use in the ultrasonic cleaner. I prefer a mixture of an ammonia cleaner and water. There are many precision cleaner liquids used by people that restore clocks and watches, some that are waterless (some petroleum distillates) and some with and without ammonia. All work very well. Some devices are heated and have timers. The liquid naturally gets hot from all the work it is doing. You put the parts to be cleaned into the liquid and leave for a period of time, usually half an hour. Then you can replace the liquid with a rinse liquid and leave it for another ten minutes. Some of the rinses even contain a light oil base, insuring the lubricant gets into the smallest cracks.

Ultrasonic cleaners work by radical changes in water pressure. As the water gets moved faster than it can flow, little bubbles are formed. As these collaps, they literlly pound the surface. Ultrasonic cleaners need to be used carefully in order to be effective. The correct liquid, cleaner, the right location of the parts in the cleaner, and the right temperature all determine how clean the parts will get. I use a Health Sonics cleaner and my favorite cleaner is Alconox.

The earlier warning about dismantling the mechanism completely can be ignored if you have a ultrasonic cleaner. The liquid soaks the entire part and bubbles explode on all surfaces, even deep in hard to reach places. This method will remove everything. I have been tempted to just put an entire coin mechanism or score reel into the bath, clean, dry and oil. But I always end up disassembling the mechanism for the fun of it, just to see how it works.

There is one problem using an ultrasonic cleaner. Try not to place dissimilar metals in the liquid at the same time and change the liquid often. It is possible to stain some of the metal parts with particles of the different metal through a chemical process I do not understand. This happens on bare metal, not plated parts and usually happens only when you leave the parts in the bath for extended periods of time. Usually a piece is clean long before it gets stained and it is only because I forgot it for a long time that this happens. The stains can only be removed with steel wool or some other aggressive process. The ultrasonic cleaner will remove the blueing on metal parts, like some of the leaf springs. These will have to be coated again with material available at most gun or machine shops.


Another modern cleaning machine is the automatic dishwasher. My goal is to have an old one in the garage, then I will not have to compete with my wife for space in the one in the kitchen. I put all my coin boxes through the pot scrubber cycle.

Finally, I have a blast cabinet. This uses compressed air to blast glass beads or walnut shells at the part needing cleaning. The dirt and oxidation are literally blasted off. It is important to used the right media, to mask off any bearing surfaces or artwork, and to use a compressor with sufficient power. The results are impressive, as all stains, oxidation, dirt and old grease are completely removed, making the metal look like it just came from the foundry.

Special care should be taken with parts that have decals or paint. All the chemicals mentioned will remove desirable markings. Test chemicals on a hidden area to see if it attacks the paint. Cover the decal with masking tape, foto/frisket film, or even paint it with a clear polyurethane or clear nail polish. These will stabilize the decal so the other parts can be cleaned more aggressively. Even these should be used with care as you can etch or pull the decal from the mechanism.


Now it is time to reassemble the mechanism. Modern technology helps here as well. There are better oils and grease that protect that good-as-new mechanism. I put oil on the metal parts that slide, lithium grease on those that feel some pressure or push on each other, and silicon on parts that are not metal, like plastic or rubber. The important thing is to use only as much as necessary and to remove all excess. Oil and grease attract dirt, which is grit, which will wear and slow the mechanism if allowed to collect on the surface. Use only a small amount.

You will invariably forget how a couple of pieces went together. The wonderful thing about a well used device is that there will be nice wear patterns in the metal. You can see how things worked and how they mated together. These wear patterns often point to how the device goes back together. In fact, in automotive mechanics, you are taught to make sure mating surfaces are allowed to continue mating in the same way. Take a careful look at that gear or spring and see where it was attached before.

Most of all, have fun. I take great pride on restoring a pinball machine or clock, or the Seeberg Shoot-the-Bear I am working on now. It is satisfying taking a dirty, neglected, old piece and restoring it to a pleasing, working, and enjoyable amusement device.