Symptom: Chain Rub

Cause: You've just torn your crank arm off!

Sounds weird, I know. Usually chain rub, that grating sound as your bike chain scrapes against something, is caused by the front derailleur being slightly out of position, and the chain rubbing on some part of the derailleur as it comes off the big chain ring near your pedal and crank assembly. So, when I hear chain rub, I look on the right side of my bike to see what's scraping what. This happened to me as I was coming off my last climb of the day, and it was loud and embarrassing. Also, chain rub gradually gets louder, as the derailleur slowly gets more and more out of position. A stretched out shift cable here, vibrations loosening the adjustment screws there, over time these things will get worse and so will the scraping sound. Not so, this morning. Sudden, loud, annoying.

I got off my bike and saw my chain was pushing on the derailleur, and not just slightly, but by a lot. Was my chain old and stretched out, so it was on the wrong cog? That's another usual suspect. I tested all the gears and the shifting, and the chain was landing on the right spot, but the front derailleur just wasn't happy about it. All these areas of the bike are on the right side. Never did I think to check the left side of the bike. Well, I figured I would just roll over to my bike shop and let them figure it out, so I called them just to let them know to expect me. I said, 20-25 minutes. Heh. not even close. 45 minutes. Why? My left crank arm fell off twice as I tried to baby my bike over to Incycle in Pasadena.

Oh, so that was why the chain ring was pushing up on the derailleur. With the left crank loose, and apparently no longer attached to the dowel, the right side of the pedal assembly had moved to the right, pressing up against the derailleur. That's not a good thing. I found that out as I pushed off from the side of the road after testing the shifting, and my left leg came down, and just pushed the left crank arm right off my bike. Clunk.

Thankfully, I always carry a multitool with all sorts of allen wrenches, so I reattached the left crank as best as I could, and set off to the bike shop. Every stoplight was my enemy, because starting from a dead stop and clicking back in gave the best chance for pushing the arm laterally away from the bike. So, of course, it happened one more time, after crossing an intersection, and my left crank arm was just dangling from my cleat. It's really easy to clip out of a pedal when you can kick the ground with it.  "Okay, multitool now goes in back pocket," I thought to myself, "then I won't have to dig it out of saddle bag again." Yes, I don't use definite articles in my own thoughts. They're my thoughts, I know what I'm referencing!

I made it to Incycle, and the mechanic immediately saw what was wrong and broken. Let's take a look at what I'm talking about here:

Nice brand name placement there, Shimano.

You see that silver, round connector? On a 2010 Shimano Ultegra crankset, that thing is black and plastic. And, evidently, doesn't like constant torque throughout the pedal stroke. Silly me for trying to maximize my effort. Incycle just replaced old and busted with the Durace version, which is nice and aluminum. My old Shimano Ultegra crank also used an aluminum connector, and lasted 19 and a half thousand miles. This black, plastic crap only lasted 3300 miles. According to the Incycle mechanic, my busted connector was the second one he had to replace this week. I think Shimano needs to go back to using aluminum. And now, I have an Ultegra-Durace hybrid crankset. Also, I can now say my pedal stroke is so over-torqued, I ripped a crank arm off my bike. Unfortunately, the mechanic said you don't have to be that strong to do it. Strong enough, I say!