This is a Longines 9782 gents dress watch belonging to my uncle. The stem appears to have been over torqued, and the the crown has broken off with part of the stem still inside. The problem here is that there is insufficient stem protruding from the crown to remove it easily.
As with many other posts on this blog, you'll have to forgive the poor macro-photography on the part of my camera. Here's the offending crown:
I've decided to chuck the stem, turn down a very small portion of the crown thread. This will expose the broken piece of stem, which I will then be able to extract. Unfortunately, I was unable to chuck the crown successfully as the crown kept wobbling off centre. To remedy this, I'll turn a small carrier which will hold the crown true, allow it to be turned down. The crown is 2.94mm in diameter, so the carrier is turned down to around 2.93-2.95mm (the measurement differs slightly due to wear on the crown knurling).
A test fit:
The crown and carrier chucked ready to be turned down slightly.
Finished crown with my thumb for size comparison. The female part of the crown thread is about 0.8mm shorter than it was originally.
A test fit on the new stem:
Final photos of the movement cased will follow...