I took the opportunity to improve my bike mechanic skills, and replaced the chain myself (rather than going to a shop). Aside from anything else, I think it's useful to know how a chain tool works, just in case I have to make an ad-hoc repair when I'm in the middle of nowhere. So, it makes sense to practice at home, when I can take my time and look things up online. I also replaced the rear cassette (cog wheels to change gear) at the same time.
So, I was back on the road in May. Unfortunately, the new chain only lasted a month, then it snapped too. This time, I'd only gone 258 km. I don't know whether I just got unlucky (dodgy chain) or whether I did something wrong when I fitted it.
After that, I procrastinated for a while, but I finally got round to fitting another new chain recently. I carefully documented the process each time, and I was planning to post step by step instructions here. Unfortunately, this didn't quite work out that way.
I went out for a test ride at 2am, when the roads were pretty clear, but I only got halfway round the block. Just as I was turning at a junction, the rear wheel locked up, so I had to hop off and carry the bike over to the side of the road. I'm glad that didn't happen in heavy traffic!
Checking the bike again in daylight, I saw that the rear mech (derailleur) had somehow got wrapped around one of the spokes in the rear wheel:
I'm not quite sure how I managed that. I couldn't see any easy way to get it loose, short of applying brute force. So, at this point I decided that I was out of my depth and I should turn to the experts. I went to a local cycle shop, and they took a look. They were able to get the mech free, but they discovered a new problem: the hanger (that connects the mech to the frame) was bent:
(If you draw a horizontal line across the middle of the cog wheels, you can see that the adjacent metal is almost in a banana shape.)
Under normal circumstances, they would simply remove the hanger and replace it. However, in my case the hanger is actually part of the bike frame, so it can't be removed. Another option is to bend it back, but that might weaken the steel, and they're not willing to risk it.
This frame was handmade by Roberts Cycles, but they're now closed while Chas Roberts takes a sabbatical. I've emailed one of the mechanics who used to work there, to see whether he can take a look; I don't know whether it's possible to de-weld the hanger from the frame, or whether I potentially need an entire new frame.
I'm also not sure about the cause and effect here: did the broken chain pull the mech out of alignment, or did the chain snap because the mech was stuck in the wheel?
I actually have two bikes: the touring bike and a Brompton (folding bike). In theory, that means that when one of them has mechanical problems I can switch over to the other one for daily use while I repair the broken one. In practice, it means that I tend to put off the repair, because I have another working bike. Then the second bike also develops a fault, and I wind up with two broken bikes and nothing to ride. I've been in that situation for several months, but it's now time for me to focus on the Brompton: either fix it myself or admit defeat and take it to a shop.