I currently have an otherwise nice Hamilton 18s 938 on my bench. It runs good dial up and dial down. But, on occasion, it will stop suddenly in one of the vertical positions. I noticed that each time it does that, the fork ends up right in the middle of the banking pins (not touching either one). I believe this points to the guard pin/dart hitting the safety roller. And, the fix is to slightly shorten the guard pin.

I am just looking for concurrence from others that I'm on the right track. Or, what else could it be?

Thanks!

Does it also stop, like that, when it is stripped to the movment only? Positional inconsistency, in the vertical positions often points to a balance that is out of true or in need of poising.

But to stop in the vertical position... I'd look to something like a hand dragging or a tight canon. If the movement is still doing that without hands or canon.... then, my first thought would be a cracked jewel that is catching a pivot on the side (or worse... that has roughened up the pivot itself).

Have you rule out all these?

Thanks for the response, Peter. I checked all the jewels and they look fine. I looked at the pivots and they look fine too. I also found that the same thing happens without the cannon pinion. If I move it very slowly, it won't stop. But, if I move it quickly, it stops suddenly. The guard pin always ends up right smack in the middle between the banking pins. I know it is darn near impossible to diagnose without the watch in front of you but I appreciate any further ideas for things to check.

Thanks again.

Well, for anyone that would like to know, I did figure this one out! The problem was that the roller jewel was ever so slightly too large for the fork. It fit enough to run (rather well) in the horizontal positions, but would catch and stick in the fork if moved to one of the vertical positions, immediately stopping the watch. I guess I always thought that a roller jewel that was too large would be obvious to detect because the watch wouldn't run at all. This was one of those "gray" areas.

I can't believe how much I'm learning working on these amazing little machines...I love it.

I'm glad that you found the problem and amazed as well.

I don't think I would have ever suspected that. I would have probably checked for the roller jewel, made certain that it hadn't slipped and... that would be that.

How did you ever think to actually measure it?

Well, Peter, I guess I was stuck on the fact that it would stop with the fork exactly in the middle between the banking pins. That is why I was thinking the guard pin might be too long. You stopped me from attacking there with your post...thanks for that. Probably blind luck that I was fooling around and decided to hold the fork up to the roller jewel and noticed that it fit quite snuggly, rubbing on the sides. So, I replaced the roller jewel with a slightly smaller one....and it worked!....even a blind pig finds a walnut once in a while.

I actually thought that the guard pin might be doing it but.... I couldn't figure out how it could have gotten that way. I've seen some pretty butchered watches but they usually leave the guard pin alone!


The 938 is a nice watch. I have one and it was one of the first expensive watches that I bought. Still, by the time I'd get to measuring roller-jewels, the watch would have been flattened by being thrown against the wall!

Opps! Did I just violate the ethics code?