So, I refurbished the transmission on the tandem before our cycling holiday, and on the evening before we're due to head north, I discover a serious problem with the chainset, and the thing needs to be replaced...the main (right hand) drive crank is seriously mangled and isn't in line with left hand crank. The granny ring also now strikes the chain stay. Cue phone conversation with the excellent Spa Cycles of Harrogate, and I've arranged to collect a Stronglight Impact tandem chainset en route to Edinburgh tomorrow.