More often than I would have thought likely I come across (Hamilton 987 series) wristwatch movements with a cracked jewel. The jewel is still firmly in place but there is either a crack line or a tiny piece which has flaked off.

Is this likely to have ocurred when the jewel was inserted, or at a later date ? What are the implications of leaving it alone in cases where a replacement is difficult to obtain ?

dan

Dan,

Here is a discussion we've had on cracked jewels.

Here's a handy chart about
cracked jewels and what
running on them can do.

That's neat, Andy.

From the shape of the pivot, can we conclude that these are balance jewels (capped)?

In the worst cases, I've been able to SEE worn bushings in non-jewelled trains. They look slightly oval. I've understood how they would effect performance but I've never considered how a worn bushing might wear the pivot. Do you think I'm correct in supposing that, over time, worn bushings will also effect pivot wear?

They say it's a balance pivot so I would assume its capped but I believe it would apply to any jewel capped or not,the sharp edge of a cracked jewel can at times act like a cutting tool against a steel pivot. The brass bushings of a clock being softer then the jewels of a watch would of course wear first and much faster then the steel running in them unless the brass bushings have contaminants embedded in its surface that are harder then the pivot like the time I found metal polish caked in the bushings of an old clock in which case anything can happen. In theory the random piece of hard grit or dirt that gets trapped in a soft bushing will work itself down into the bushing to the contact surface or even a little below it before it has a chance to do too much damage but caked metal polish is something completely different ,you cannot make a machine ***** proof.
Regards
Anthony