Emergency on-the-road Crank Repair
 

I thought that I would share this tale in case one of you has ever forgotten to check the tightness of your chainring bolts. I went out for a ride this morning on my vintage 1987 LeMond (pre Trek) and came to a steep hill, shifted to the small ring and 28 tooth cog on the freewheel, stood up, the chain came off, and before I had time to unclip, blam, I was lying on the pavement. What happened? All the bolts holding on the chainrings except one had fallen out! So now, what to do? Phone my wife, but she had forgotten to bring her cell phone shopping. So, after a bit of pondering, I removed one brake pad and bolt from the rear brake and used it replace one of the missing chainring bolts. The repair allowed me to pedal home without further problems (using the front brake only). Now, go check your chainring bolt tightness.http://bikeforums.net/attachment.php...hmentid=213406

Even one missing chainring bolt can cause serious problems:

http://i.imgur.com/YtNks.jpg

slick idea ! Thanks !

I'm trying to figure out how you ride for long enough with loose chainring bolts that all of them but one fall out. That doesn't happen overnight.

Nice job on the emergency fix though.

How did I ride for long enough with loose chainring bolts that all but one fell out? I think that even with two bolts it rode normally (I probably rode ten miles with only two bolts), and then the next one fell out........ Before the ride I lubed the chain so I just did not look for the problem. I installed the crank on the bike perhaps ten years ago and no problems until now.

A symptom of loose chainring bolts that I have noticed is sluggish shifting from the small to the large ring. When the bolts are loose, the chain pushes the ring to the outside first before shifting onto it. If you tighten up the bolts then the shift becomes far quicker. I've also had chainring bolts occasionally loosen on me; I now use Loctite on them, check them occasionally, and pay close attention to them if I'm having trouble making the small to big shift.

Wow! What actually happened to do that much damage to a chainring? I'm certainly going to check the chainring bolts on all my bikes now!

Didn't you hear the crankset knocking? Seems like it would have made all kinds of noise.

Don in Austin

I've both lost chainring bolts, and mangled a crank like the photo above on a test stand (two separate incidents). In my case the bike I lost a chainring bolt on was a 1970-1971 bike, so even when maintained it made a bit of noise. There really wasn't much more noise from the missing bolt. I finally noticed when I was going up a hill and the chainring started moving enough to make the chain rub the front derailer. As I recall I actually shoved a stick in to replace the bolt and rode the last half mile home slowly. On the other hand, the time I broke a chainring on a test stand it was due to applying too large a load, even with all of the bolts attached. Once you get it a bit off center, the sheet metal sprocket twists right up.

That appears to be a fixed gear, thus, it is likely that the torque applied to the relatively thin and large chainring on the small bolt circle lead to the chainring merely folding up. This is one of the reasons why track cranks have such a large bcd (144mm) and thicker chainrings.

Cheers
lverhagen