Diagnosing mystery bike noises; Chainring photos: new vs old
My replacement Ultegra crankset arrived yesterday, and I decided to go ahead and install it. I was sort of on the fence about installing the new crankset because, as it turns out, I don’t think the original crankset was quite at the end of its life. Maybe. I’ll get to that in a minute. Before I do, I’ll recap why I ordered the replacement crankset in the first place…
Last week I was chasing down a mysterious noise that started on Saturday, October 18th, which was a hilly 81 mile (130 kilometer) ride. Originally I suspected that noise was drivetrain related, as it was intermittent, and seemed to occur most frequently when I was climbing or putting power into the pedals.
I took the usual steps to discover the source of the noise: I swapped my shoes out, swapped the pedals out, pulled the cranks and checked/cleaned/re-greased the bottom bracket bearings, oiled and lubed all moving parts, inspected the frame for cracks, made sure the chainring bolts were tight, greased the QR skewers and so on. Unfortunately none of those diagnostics bore fruit, and the annoying noise persisted–in fact, it was getting worse.
It did not. So I replaced the cassette (Ultegra CS-6700 11/28T), which had a little over 6,000 miles on it. I normally would have replaced the cassette with the chain anyway (I replace the cassette every second chain), but I was trying an experiment to see if I could get three chains out of this cassette. The new cassette did not fix the problem.
So I returned to my bike shop, and put my bike in the work stand. I turned my cranks and carefully watched the chain from above. There was a definite wobble: the chain moved inboard relative to the front derailleur cage at a particular point in the rotation. It didn’t quite hit the cage, but I reasoned that under power (which is when I was hearing the noise), perhaps the frame flexing was enough that the chain was rubbing the derailleur cage, creating the noise.
My crankset/chainrings had a little over 12,200 miles (20,000 kilometers) on them, and once I saw that wobble I figured it was time to replace the crankset. So I placed the order (Shimano Ultegra FC-6750, 50/34, 175mm).
I knew the crankset would not arrive before this past Sunday’s 100 mile ride, the Horse Farm Hundred (that ride report is in yesterday’s blog), and I was a little nervous about doing such a long and fast-paced ride with an undiagnosed mechanical issue.
So this past Friday after work I was sitting in my bike shop with a dumb look on my face, staring at my bike and scratching my head. Wiping some drool from my slack chin, I glanced around the garage, when suddenly my spare wheelset caught my eye.
I removed my rear Zipp 404, popped in the spare wheel and did a couple miles around my neighborhood. Silence. Sweet, sweet silence.
I should have performed this step much earlier in the troubleshooting process. In fact, the wheels should have been one of the very first things I checked. It’s a safe bet that you’re much smarter than I am, and would not have made this error; if not, though, I hope you learn from my mistake.
Anyway, at that point I knew the problem was almost definitely the rear hub (spoiler alert: it was). That was an entirely different nightmare, which you can read all about here.
Anyway, I got the hub overhauled in time for Saturday’s club ride, and my bike ran perfectly smooth and was very quiet. My bike also performed flawlessly on Sunday’s Horse Farm Hundred ride.
Which brings us to yesterday. My shiny new crankset arrived, and I considered not installing it just yet. I kept thinking about that wobble, though, and I decided to go ahead and replace the crankset, and would simply keep the old crankset as a backup.
After replacing the crankset the wobble I noticed is now, of course, gone. I think it was probably a good idea to go ahead with the replacement.
That said, I’d love to get some learned opinions from very experienced/professional bike mechanics, so I took a few photographs of the old and the new chainrings. You’ll notice the inner ring is in nearly new condition and shows virtually no wear, as I do 95% of my riding on the big ring. The big ring definitely shows a significant amount of use–and there’s the issue of the wobble I noted earlier–but I’ve not had any issues with skipping or shifting. Thoughts?
Here are the pictures (click to enlarge, you can progress forward and backwards while enlarged with the arrows on the left and right):