A watch can be devoid of oil, and run perfectly.

This watch I've worn for ten years, then all of a sudden it started losing 15 minutes at a time. So I stopped wearing it.



It's a Hamilton Custer from about 1936; cell phone from around the same era. But, I need a watch that will easily go under exam gloves. So I went to the bank, and pulled this from the safe. It hasn't been touched in 25 years.




It's a Hamilton Gilman from 1947. So I wound it up, strapped it on, and it's keeping perfect time.

Now, one would assume after two and a half decades, all the oils would have dried out. So, it appears to be true that accurate time-keeping in not a good indicator of the need for a service, and I probably shouldn't even be wearing it. I have to confess, however, that I don't really understand how it could be performing so well with the assumed increased friction on all parts due to the lack of lubrication. Be that as it may...

 

I assume that the oils may have dried out without any dust. So the friction is not too strong to stop the watch. Consequently the hairspring should be in good condition with no rust and still had a good elasticity.

The watch was kept in good storage conditions

 

It’s a matter for the owner to decide. Does he want the watch to perform well for a long time with only routine maintenance, or is he satisfied that it run well for a short time, then face the prospect of an expensive repair with lots of parts, or perhaps ruining the watch beyond repair. Decide before you find yourself in the latter situation.

 

I hear Speedmasters fit perfectly under exam gloves

 

I don't know if this will help but, I wrote most of this for someone else and it generally reads across. I'm talking about a typical pivot in a jewel here.

If we look at a Stribeck diagram then watches are over on the left in the boundary lubrication area. Car engines are further over on the right so watches don't work like car engines and there are no decent comparisons to be made there, such as starting your car every week or two to keep the oils flowing. I know some people think there may be so, I mention it.

For boundary lubrication, we form a layer on the bearing surfaces to smooth out the imperfections and this enables most of the bearing load to be transferred through that layer and not by direct contact between the pivot and jewel. We use highly polished pivots anyway but they are still not perfectly smooth. The oils we use are specifically designed to do this and to stay in one place. That means if we put the oil in the jewel cup, it will stay there and form the layer on the two surfaces.

You can liken the above to snow skiing and waxing the bottom of your skis where the wax is representing the oil. While you have oil, there is not any strict metal-metal or metal-jewel contact so, very little wear.

Contaminants (cleaner/dirt/dust) in the oil will make a sort of grinding paste and can cause a lot of wear very quickly.

One difference with cars, let's say a main bearing on a crankshaft, is that the oil doesn't stay in that location very well so, it eventually drains away into the sump and the two surfaces become dry. It's not designed to stay there and is designed to flow because when you start the engine, oil is fed at high pressure to the bearing and forms a film thicker than the surface roughness of the parts. So, the crankshaft is, sort of, floating on the oil (the same effect as water skiing, as opposed to snow skiing above) and the surfaces don't contact. If the pressure drops too low, then you'll get metal to metal contact. We don't have the high pressure option in watches and also don't need it because the parts move slowly with low load.

The problem with the boundary lubrication used in watches is that it doesn't work with the sort of speeds, loads and temperatures found in an engine so, it's not suitable.

Going back to why a watch will still keep fair time even when dry. This is isochronism. If you've ever had a pendulum clock, you'll know that the timekeeping is similar whether the pendulum swings a fairly small amount or a large arc. It's the same in a watch where a smallish balance swing, say 160 degrees, will often show a very similar daily rate to a large swing of say, 300 degrees. The typical specifications allow a larger positional variation after 24 hours from full charge, when the swing may only be 160 degrees, but it's not usually much - say 35 seconds rather than 25 seconds/day.

If there is a conclusion, it's that a watch that is dry and has high friction will have lower balance swing (amplitude) but, that does not necessarily mean it runs dramatically different to when it was serviced. You would expect the power reserve to go down but, the bigger issue is that you now have metal-metal or metal-jewel contact that will wear out the parts. In the same way, even when there is oil, if that oil is contaminated, then you will get wear.

I'm not a tribologist but we learn this on watchmaking courses and the first aim of an intervention in a watch is usually specified as "conservation". We are trying to keep your watch in good order for the next X years so, cleanliness and lubrication are the most important aspects.

If you're not worried about replacing parts (modern or cheaper movements are good examples) then run it dry if you wish. I wouldn't recommend it with vintage watches where parts are often expensive and difficult to find.

Cheers, Chris

 

Wonderful; thanks Chris.