I have been doing endless detective work tracking down a problem in my Gran Tourer. When I ride it for more than about 5 miles, the bottom bracket would start to click and/or make some audible clunks. This gets worse the more miles ridden. However, after letting the bike rest for several hours, it would be smooth as silk again.
However, ostensible bottom bracket issues are notorious for being due to other causes, from seat creaks to hub issues to pedal issues to headset issues to ... And I've run them all down, greasing, swapping cranks and bottom brackets, lubing the saddle, rebuilding the headset, repacking pedal bearings, installing different pedals, and endlessly fiddling with bottom brackets, from teflon taping the cups, caged/uncaged bearings, tight adjustments, loose adjustments. I've probably left a few things out, but you get the picture.
The worst part of this ordeal is that each test ride begins anew with an increasingly smooth and quiet ride - all this debugging work is really smoothing out the ride. But then after a few miles, the exact same behavior arises. And one must go on a ride of reasonable length, not just a quick run around the block once or twice. This stretches out the turnaround time for new avenues of investigation.
But I think by simple process of elimination, I've run down the cause, or causes, I should say. This evening, I spent more time and care installing and adjusting a loose bearing bottom bracket and crankset than I ever have before. Following this, I didn't have time for yet another five mile loop, so I sat and turned the crank, listening to it with my fingertips on the arm and the frame.
It seems to display a tight/loose pattern per revolution. This indicates that the bottom bracket cups are misaligned, which can have two causes. The first is that the bottom bracket shell needs facing. The second is that the right and left hand side bottom bracket threads are misaligned.
Facing a bottom bracket is a routine chore. The shell appears to have been faced once, but there is no way for me to tell if it was done adequately. Misalignment of threads is a far more serious issue, which could entail having to rethread the bottom bracket for Italian threading.
If I had a spare cartridge bottom bracket around, I could easily diagnose this. Misaligned threads would make installation difficult or impossible. But if it did install easily and then the creaking and clunking disappeared, the facing is then the issue.
But while I can't even begin to count how many Suntour V series derailleurs are cluttering the shelves, getting underfoot, like a population of cats in an eccentric's home, I don't even have one cartridge bottom bracket around. That says something, although I'm not sure what.
I also don't have the conventional tools to diagnose and remediate facing and threading issues, so it is time for one a very infrequent cry for help to a LBS. I really hate to do this, it is like admitting defeat, but even the DIY obsessed have their limits.
Like buying a four hundred dollar facing tool to do a job that the LBS charges thirty bucks.
So I'll be tearing down the crank and bottom bracket yet again and outsourcing this job.
I sure wish I had figured this out before I got done building this bike, but I was only taking it for relatively short spins during this period. I had noticed a little fritziness in the bottom bracket, but I assumed that the usual repack or even replacement would quickly sort that out when I got around to it.