This early S Copal shutter looks like a close copy of the British Epsilon. This one from a 1953 Olympus Six was completely corroded and seized. With no choice but to strip it and clean it, although after re-assembly the shutter was slow, so further investigation was required.
I found that the shutter drive ring was bent, pitted and wasn’t running smoothly on the housing (a sure sign of being forced). This caused binding and slowed all speeds above 1/25s.
I used 1200 and 2000 grit wet / dry paper and Solvo to polish the internal ring to remove the pitting and straightened the pins. Upon reassembly, the shutter matched selected speeds of 1/25s up to 1/100s but was still 1/2 stop slow at 1/200s – a tell tale sign of a tired booster spring.
The slow speed escapement spring was also tired which required it to be closer to the housing centre to gain accurate speeds up to 1/5s. Unfortunately 1/10s was now failing, so after much trial and error I decided to live with the closer escapement placing and re-profile the 1/10s speed ring step.
The result was a shutter that was within 10% of all speeds up to 1/100s and 30% slow at 1/200s…….good enough for B&W!