Crank arm fell off..wtf?
Was on a ride today I noticed what I thought was some strange play in my pedal/cleat. Sometime later, I couldn't shift into the big cog and then the chain fell off a mile before the ride ended. Turns out the crank fell apart. The left side arm fell right off. I thought I broke the threads as a strange, small ring (turned out to be a seal) was on the ground. Bah.
Assuming it sheared apart, I went to the local shop to discuss the FSA warranty (it's a FSA SL-K compact). The mechanic (at a great shop in Ballston area of Arlington VA) cleaned it up, examined it and realized that it just came undone. He couldn't explain it other than saying it may not have been torqued correctly when it was installed (600-700 miles ago) (I purchased it at a different shop). He did notice, however, some grinding/"chewing" marks in the teeth of the spindle and in the grooves on the left crank arm probably caused by today's ride after it started to loosen. He reinstalled it using loctite and some anaerobic solution of some sort.
Thankfully, he doesn't think it should affect much again. Is this an unusual occurence? Will the scars on the grooves and/or teeth cause any problems.
Not unusual at all when the bike-shop employee doesn't use a torque-wrench and get that bolt to the proper specs. Without an automotive-style 3/8" ratchet wrench, there's no way anyone's gonna get a crankarm-bolt up to the proper torque of around 27-35 lb*ft.
Unfortunately in your case, the mating teeth between the crankarm and bottom-bracket spindle has been chewed up by the looseness and wobbling. This is invariably a rapid downward spiral where the wiggling motion it allows will cause even faster loosening and falling off crankarms. Keep an eye on it, if it falls off again, you'll most likely need a new crankarm.
Last edited by DannoXYZ; 06-24-07 at 02:14 PM.
Thanks. That's what I feared. The extra play in the grooves might cause it to loosen up. Crapola.
I don't see how the left crankarm loosening would affect your shifting...unless you're running left-hand drive?
I've seen certain brands and models loosen several times (even when properly torqued) and the manufacturers have varying viewpoints on the warranty issue. At least one of them feels if the rider notices a loose crankarm, yet continues to ride on it until it falls off, it is rider error and not covered under warranty.
Originally Posted by ahsposo
FSA SLK cranks are known for having the fixing bolt on the left crank arm back out letting the arm fall off. It's a design flaw. Use the search function here and read the reviews at roadbikereview.com. Supposedly, replacing the alloy bolt with a steel one fixes the problem.
I can understand the varying warranty issues, but when it happens on a ride and the rider cannot figure what is wrong until it is too late, I think the warranty issue should hold. In this case, unfortunately, there is no telling whether the mechanic who built it up messed up on the torque. Seems less likely since it has been many many months since I purchased it.
As far as the shift, best I can tell is that it started to come undone and shifted drive side outward. The FD worked fine, but I guess it couldn't reach the big ring once is started to come unscrewed.
Ah, I didn't realize that crank was a two-piece system. My bad.
Originally Posted by deskjockey
I hear you regarding the warranty, and agree for the most part. If a certain crankset make and model loosens chronically, the manufacturer should either cover it by warranty, or just issue a recall. As with so many things though, they try to pass it off as mechanic error, rider error, sunspots, etc. If they choose to not do anything about the issue, it's the shop that always gets blamed and has to eat the costs. After all, the manufacturer is never seen, but the shop mechanic is in the public eye and subject to scrutiny, belittling and being poked in the snoot.
FYI: Most bikes sold through shops come with the cranks already installed at the factory. It is when the wrench makes the assumption that factory torque specs were applied that it's their fault anything loosens up. Nice way to pass the buck.
Last edited by Wordbiker; 06-24-07 at 11:08 AM.
Originally Posted by ahsposo