Eccentric motions

When I got my tandem bike for my wife and I to ride I was stoked. I had wanted a tandem since I was about 14, when I first began having problems with my riding companion keeping up with me. It seemed like it would be more fun, more speed, better communication and cool all at the same time. It proved to be all of that and more.
After a few hours of riding the bike creaked like a cheap department store bike. Turned out to be the eccentric. For those that don’t know about eccentric bottom brackets, because you have 2 sets of cranks and 2 chains on the tandem, there has to be a method of tensioning the timing chain and by far the most common is that the front bottom bracket sits inside an eccentric adaptor in a much larger than usual frame shell. Hard to describe, but really very simple. By making the BB shell big and positioning the axle off centre, the position of the crank varies with the rotation of the adaptor piece.
Some eccentric systems use a pinch bolt arrangement. This is the cheapest method and it requires cutting the BB shell at the production stage. Most use a wedge anchoring system such that one segment of the round unit expands against the other when a bolt is tightened. Adjustment becomes a pretty simple rotate, hold, tighten. The bolt requires quite a lot of preload to keep the whole unit in position (remember all the crank’s force is trying to rotate that).
So the solution to the creaking problem was a healthy layer of Shimano anti-seize compound on all individual pieces prior to reassembly. You have to remove the cranks from the BB to do this, but current 2-piece cranks make this easy. Any little bits of dirt in the assembly, and they do seem to find their way in there during riding, contribute to the noises made. The anti-seize is not a permanent solution, but it does silence the tandem for many weeks (i.e. at least 1500 km riding).
What about the single speed?
Most people convert their old hardtail to a single speed via a tensioning gizmo that goes in place of the rear derailleur. A more recent, and more elegant, solution is the eccentricizer BB which produces only a tiny amount of adjustment, but enough that you can make it work (this device moves the BB bearings outboard of the frame in current 2-piece crank practice but the bearings are housed in an eccentric housing that moves the crank axle from the centre of the shell to nearly touching the shell).
Dedicated single speed frames, such as my Rig and the Trek 69r, have two different solutions. The Trek has sliding dropouts and a conventional BB. The Fisher uses a tandem style eccentric BB and normal dropouts. The Fisher does creak - mine has just started after several hours of use. A look at the web proves that everyone’s creaks. Many people seem to think that the noise cannot be quieted, ruining the quiet bliss that is single speeding. Tonight I hope to prove them wrong when I disassemble the eccentric and cover it in anti-seize.
One nice thing about the eccentric is that you can choose ground clearance by rotating the cranks upwards, or you can choose centre of gravity by rotating the cranks downwards. It even lets you try both to see how subtly the BB height in a frame design affects handling.

Keep those eccentrics greased and they’ll do their job quietly.