We haven't ridden our Thorn tandem much in recent years. However, on Tuesday we did 22 miles on it, including a bit of the Peddars' Way. I noticed part-way along that the drive side pilot's crank was loose. As luck would have it, we were pretty close to the A11 crossing where there is a rest area with the "Pitstop" burger bar. I asked J. Random Motorist if he had any tools and he did indeed have an allen key big enough (I didn't in my portable tool kit). He tightened it up and it got us home.
We've just put the tandem back together and I noticed it's loose again. It seems to me that it's the sort of thing that, once it has started, it's likely to carry on loosening. This week is the first time this problem has occurred and we've done almost 15000 miles on the tandem in almost 16 years. I have a correct-size allen key somewhere, which I haven't found yet, but I had a Topeak multi-tool in the cupboard with the right size allen key on it. I've done it up as tight as that could do, but I feel that it needs more torque.
Assuming it comes adrift again, what should I replace? The whole BB or just the cranks?