After a long pause I have returned to testing the clock mechanism. I have made some repairs to the components that make the chime work at the right time and for the right number of bings of the bell. One lever had been repaired a long time ago, but the repair had failed. A spring was also rather bent and not acting well enough.
I suspect that the original repairs may have been made by my great grandfather who once owned the clock!
Initial tests show that it chimes correctly, but it needs to be run through quite a few cycles to have some confidence that the repair has worked.