EJ123

About 6 months ago, the left crankarm of the Fuel became wobbly as I pedaled, and after about 3 seconds later it just fell off. Luckily, since I carry a hex wrench set in my pack, I just screwed it back onto the bike. Usually after every 100 miles or so, I tighten that screw so that doesn't happen. Well yesterday the crank became wobbly and I pulled over immediately on the shoulder before the crankarm would fall off in the middle of traffic, heh.

And what do I find out? The bolt won't tighten at all. It feels like it got about 60% tight at one point then warps back to about 20% tight and the cycle repeats it self. What is going on?! I had my camera with me so I took a shot while I waited for a ride.



The left screw thing is stuck in the crank arm hole. I honestly can't remember if it's supposed to come out, but it's stuck there. (the circular thing with a camel/tan color goop)

DannoXYZ 

There's absolutely zero way you can get that crankarm-bolt tight enough with a little portable hex-key. You need an automotive-style 3/8" drive ratchet-wrench. Even better a torque-wrench.

This sounds like the threads in the bolt or spindle is stripped.

It's supposed to stay in there. The bolt also functions as a crankarm-puller.

EJ123

How do I fix the problem?

making

after your crank falls off it is pretty much over.

Ashen

You need a new bolt, a new bottom bracket, or maybe both. Also remember for the future, hand tight is NOT good enough for a crank.

EJ123

I never knew that, but thanks. You too Danno.

making

Nobody ever thinks my crank jokes are funny. O well.

bobn

Probably is stripped from the description. That BB looks like it needed some serious mantainence.

BikingGrad80

I use a big L shaped allen wrench for my octalinks cranks. It seems to work well as long as I apply some good muscle into it and grip the end of the long part to apply more torque. It hasn't come lose yet and I check it regularly.

Is that an outboard bearing crankset?

JanMM

Hand-tight can be ok, depending on your hands and the tools they are using.

jsmithepa

There is joke somewhere in there. Almost like ppl putting a black tape over their ENGINE LIGHT, 'coz it's annoying and they will fix it later.

making

Seems to me like a crank falling off while riding is so serious it has to be at least a little funny when joked about. Besides the word crank is a little funny. But I give, I shall try to refrain from crank jokes from now on.

wrk101

Looks like the threads on the bb are totally stripped out. Get a new bb and you should be good to go.

operator

Hand tight is ok if you're using a kilometer length cheater bar on top of your tool.

SJgunguy24

I have a Shimano XT on my jump bike and the same thing is happening to me. as I ride it makes this "pop" sound and then it gets loose. I can see clean through the B.B. so I was thinking of running a long 5/16" bolt with a washer(all grade 8 aircraft hardware) and washer /lock washer/nut combo to keep the thing from flying apart. Opinions please..... What is the strongest crankset that is made,I know BMX is usally bombproof but I need nameand models. I'm a fat guy who likes to fly. I'm 275 and the only weak link now are the is the XT crank set.

DannoXYZ 

Hmmm, it sounds like the threads in your BB (or the bolt) is stripped as well. The problem with constantly tightening the bolt is that it'll wear out the threads in the BB. Bolts, by their nature of being rolled, tend to have stronger threads than the hole that they're threaded into (which are simply cut by a tap, so no continuous grain at the surface of the metal). Over time, you'll strip out the threads in the BB axle and you'll need to replace the BB in order to keep the crankarms from loosening and falling off.

I don't know if you can run a bolt clear through the BB, the left & right side threads don't meet in the middle, so I doubt the threading is continuous.

What it comes down to is you have just ONE chance in the beginning to get the crank-arm bolt on correctly. After it comes off the first time, you tend to mangle up the hole in the crankarm and it'll never fit onto the bottom-bracket spindle perfectly after that. This leads to easier and easier loosening of the crank-arm bolt.

So on the 1st time install, do all you can to make sure the bolt stays put:

1. make sure threads on both bolt and spindle are clean and grease-free
2. use blue Loctite on the threads
3. use a star-lockwasher (split lockwashers don't work worth a cr@p!)
4. use a TORQUE WRENCH and tighten that bolt down towards the high-end of the manufacturer's specified torque

On Octalink cranks, that's about 35 lb*ft of torque. Using a puny 6" allen-key would require you to push on the end of it with 70 lbs of force! No way you're gonna do that without poking the allen-key through your hand. With a torque-wrench with 18" lever, all you need is just 23-lbs of force. Quite easily achieved with a 18" handle on the torque-wrench.

JanMM

a torque wrench is a hand tool. I guess hand-tight really refers to no tools - not this situation.