Recently I was riding my bike on not too many hard trails and I transfered onto a dirt road and while I was riding my left foot when pedalling kept moving side to side, so I thought it was the pedal then all off a sudden my entire crank just fell off and when I looked at it the nut ,I geuss, just fell off. But part of it makes no sense to me cause that would be a really hard part to just loosen over time. Well anyways I had to walk/coast it home for a few miles mostly up hill. Has anyone else had a similar problem?

Later,

Another MTBiker

Happened to my cousin while we were on a ride. The fuggers at the bike shop didn't tighten the bolt when he bought it new, and we didn't have the proper tool to repair it on us, so we all went to the bar and got drunk. True story.

I had a similar problem: the crank didn't come off, but it loosened. I took it to the shop to get it tightened, and they showed me how riding on it had worn away at the crank. I ended up having to buy a new crank, only rode on it for a few miles. Do NOT, if you haven't already, ride on a loose crank. It WILL get ruined--softer aluminum gets worn away by the harder bolt steel. Look out!

A friend of mine has his removed by a malcontent in an attempt to harm him.

Unfortunately, left side cranks falling off of new bikes is a fairly common problem. I had that happen once in my shop while a customer was test riding. I took out my frustration on the newest guy in the shop. Handed him a torque wrench and told him to check every crank arm in the shop. Never happened again in my shop. Talking to other shop owners, I know that my experience isn't unusual. Nobody wants to talk about it because they aren't proud, but it's common.

Now I haven't toured every bike manufacturing plant in the world so I don't know how they all work, but in the one that I have toured, the bikes come down an assembly line and a guy tightened the cranks on both sides of the bike from drive right side using an ordinary ratchet wrench. I suspect they just don't get the left side cranks tight enough.

I have been riding my bike for about a year, and then it happened, not over just a few days. So I think I am just gonna buy a new crank set with a cassette, a really good deal for like 129. Its a truvativ. So I hope that works out. I really like the story about getting drunk though.

Later,

Another MTBiker

MTBn' is tough on a bike. Perodic checks on the tightness of all parts, especially the crankset, BB and HeadSet are required.

Aluminum is soft, steel is hard. Under great stress, the cranks can start to deform just slightly, and that's all it takes. That taper-fit on the old style BBs will work very well, but if it gets even slightly out of square, no amount of tightening the securing bolts will help.

I don't think the designers of these parts ever envisioned guys jumping off huge drop-offs!