erbfarm

I've been riding a Specialized Sequoia for about 10 years now without any problems. I overhaul the bottom bracket each year and ever since I did that two weeks ago, the crank won't stay on the bike! First, it was just on the non-drive side. I'd hear a grinding sound, then the crank bolt would come loose. After retightening the bolt for about a week, the drive side lock ring started to loosen with each pedal stroke! I know I've got everything threaded correctly on there, I just can't figure out what is causing the problem. I think the inner bracket shell is ok. there aren't any stripped threaded on either the fixed cup or the other cup. The spindle looks ok too. any ideas?

mechBgon

From the mix of terminology you're using, it's not 100% clear if you're reporting that your crank comes off the spindle, or that the bottom bracket loosens up in the frame. Pictures might help, can you shoot photos of the offending parts?

DCB0

If a square-taper crankarm is falling off, the tapers in the arm ar most likely damaged and the arm must be replaced. THis is a pretty common problem, usually caused by the arm not being propelry tightened, and less commonly because the arm is overtightened.

As for the bottom bracket coming unthreaded, I suspect it was also not properly torqued into place during the last re-assembly. Unless the bottom braket is seized and that is why it is working its way out, or the crankarm has been overtightened so much that it has moved inboard far enough to be contacting the bottom bracket and is unscrewing it while you ride.

FWIW, cartridge bottom brackets often last for years and many many miles before they need replacing, and you can tell if they are on their way out if they develop play or excessive friction. Since replacing is the only option with a cartridge bottom braket, there is little/nothing you can do to extend its life. And seeing as the re-assembly process may have been done partially incorrectly and this caused problems, I think your problems are caused by ignoring the cardinal rule of the handyman: IIABDFI (If it aint broke don't fix it)

erbfarm

i def think I'm going to spring for a cartridge bb. just was wondering what could cause this problem since I have been overhauling the bb regularly for 10 years and never had this happen before. I did replace the crank arm by the way but the same thing still happened.

cny-bikeman

Again, you need to explain what you mean by "the same thing."

"I'd hear a grinding sound, then the crank bolt would come loose. After retightening the bolt for about a week, the drive side lock ring started to loosen with each pedal stroke"

The crank bolt (assuming you mean the bolt that secures the crank arm to the BB spindle) comes loose because it was not properly tightened. Once it does and the crank loosens enough to fall off the (aluminum) crank arm is almost always damaged enough that no amount of tightening will keep it on. You would have to replace the crank arm, not the BB.

Don't know what you mean by drive side lock ring. The BB does not have a lock ring on the right side. Do you mean that the fixed cup of the BB comes loose from the right side? Or is your right crank arm coming loose as well? Or is it actually the lock ring on the left side?

There are multiple images of BB/crank parts on the Internet. Please look at a few and explain with standard terms or give us some pics.

BCRider

I take it that he's got TWO things coming loose. One being the crank arm and the other the BB shell lock ring.

erbfarm, simply put you just need to tighten the lock ring a little harder. And when you do use a tool which doesn't crush it and lock the ring to the shell threads. Perhaps if you are using the wrong tool you're only pinching it tight instead of actually threading it against the BB shell.

For the crank arm I suggest you messed up and did not get the arm bolt tight enough. And the fist time it came loose it deformed the square taper. And when that happens it quickly deforms the square taper eye in the crank arm to where it will no longer seat correctly and stay tight. But since you've got nothing to lose try removing it, file away any burrs you see and then liberally grease the taper and tighten it up again. The grease MAY let it ride up further and swage to shape to some degree. And don't spare the torque for this. You have to jam this thing on TIGHT the first time if you want any chance of making it work.

DCB0

I have seen many times a damaged crank that falls off and is repeatedly re-installed results in a slightly, and imperceptably to the naked eye, damaged taper on the spindle, and it is unable to hold on a new crankarm. A new spindle will fix this, although loose spindles can be hard to come by so an upgrade to cartidge BB (along with another new crankarm) is probably the fix.

My comments above about cartridge bottom brackets and IIABDFI were made because I thought you already did have a cartridge bottom braket. I assumed you meant you bought a mid 2000s spec. sequoia new and had been reguilding the BB every year since. But then I looked at you sig line and saw the '80 something SPecialized Sequoia' and realized you probably do have a rebuildable cup-and-cone BB.

cbuddy2005

A damaged crank arm will wobble even when the bolt is tightened and thus work the tightened bolt loose again. maybe some Loctite on the bolt threads as aquick, cheap, TEMPORARY fix. I think The BB is fine, crankarm not so much anymore.

onespeedbiker

I trying to wrap my brain around the idea that a section of aluminum could somehow deform hardened steel. Then you say that replacing the spindle will fix this problem but you also need to replace the crank arm; are you saying that it is always necessary to replace both spindle and crank arm anytime the crank comes loose? Perhaps you were responding to the OP
But I'm guessing that the same reason the first crank came loose is why the second came loose; under torquing. I have never had a SQ crank come loose on the dozens of bikes I own. I put a very thin film of grease usually I just wipe it with a greasy rag. I then torque the crank bolts 450 inch-pounds (I've learned that a good effort with an 8 inch breaker bar will do the trick). I then ride the bike around the block a few times and re-tighten. I can't imagine an aluminum crank doing anything to a hardened steel spindle, not even damage "imperceptible to the naked eye."

DannoXYZ 

Yeah, there's very little chance an aluminium crankarm can damage a hardened steel spindle. What is happening in cases where replacing the spindle fixes the loose-crankarm problem is that the threads in the spindle is worn-out due to repeated tightening of the bolt. Most people will not completely remove the crankarm and bolt and clean up everything. Dirt and grit will be on the threads of the bolt when they re-install and over time (10-years?), the threads on both the bolt and spindle will be worn out.

The most likely cause of these issues is insufficient torque. erbfarm, to what torque are you tightening down the crankarm bolts and adjustable-cup lockring? Check out this Park Tool - torque specifications page (scroll down). Note that crankarm bolts require 25-33 lb*ft torque! That's amongst the highest torque values used on a bike and can only be achieved with an automotive-style ratchet-wrench with 12" handle.

Well, this is a breaker-bar, but you get the idea. If you've ridden with the loose-crankarm for more than 30-seconds, it's most likely buggered and you'll need a new one. Also replace the bolt with a new one as well. In some rare cases with everything done properly, the crankarm still comes loose. I've had good luck with using a star-lockwasher, blue Loctite on the bolt-threads, and tightening it to the maximum 33 lb*ft torque.

For the bottom-bracket adjustable-cup lockring, you need to use the proper tools:

https://2.bp.blogspot.com/_8Tly19mAQz...ool+SET+BB.JPG

It's impossible to get the lockring tight enough without spinning the adjustable cup, so the pin-tool holds that in place. Pick a spot on the lockring to hook such that the two-wrenchs are about 90-degrees apart. Then squeeze them together as hard as you can (hold the pin-tool stationary). When removing the lockring on some bikes, I've had to hit the end of the lockring tool with a hammer! They probably used a hammer to tighten it!!!

erbfarm

Thanks everyone I'll try the suggestions