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Crank arm play.

Old 05-09-12, 03:48 AM
  #1  
PhilipHines
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Crank arm play.

Hi Guys

Am new to this forum, and bike maintenance etc etc, so apologies for any faux pas.

I have a cannondale R700 2005. https://web.archive.org/web/200706022...del-5RR7D.html. Done several thousand miles with no real servicing/replacements.

Recently i had a spate of my non drive side crank (left) coming off, which was a bit of a hassle. Took it to a bike shop and they said the cup on the crank was useless (i had slipped it from over tightening), and that this old FSA Gossamer was prone to coming off. SO they put and updated cup on, and apart from one time when it loosened it has been fine for the past 100odd miles. However now new play has emerged. At a certain point in my stroke, the crank jumps a bit with play.Yet the crank arm remains in the tig

I have a friend who has tools which i can use to try to tighten. He said get a new BB. What do i do, do i tighten, or new BB. If new BB (currently a FSA MegaExo integrated apparently) what size/do i have to stick to same, can anyone recommend one?

Thank you very much

Phil
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Old 05-10-12, 07:59 AM
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anyone know at all? Thanks
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Old 05-10-12, 09:03 AM
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I am not sure what you mean by the 'cup' the shop replaced but in general if the left crank arm keeps loosening and coming off you need a new crank arm.

Is the crank arm loose on what would be the spindle? or is the bottombrakcet loose in the frame? a pic or two may help
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Old 05-10-12, 10:30 AM
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Thanks. By cup, i mean cap i suppose. On the left crank there is a threaded aluminium cap, which you tighten in order to push the crank onto the spindle. When the crank came loose/off you could tell it was loosening by the movement, but also you could see it coming away from the edge of the bb, with the spindle being exposed. Currently the 'cap' is tight, there is not gap between the bb and crank, yet there is play. I'm not with by bike atm, but will double check that it isnt still the cap issue, and is definitely the bb i suppose.
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Old 05-10-12, 11:59 AM
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That sounds like it's your bb. It looks like it's the sealed bearing kind, which usually means tightening it won't really help, but you can always try. You need to get a new bb. You can get a different one if you want, just make sure it's the same size and offset if it has it.
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Old 05-10-12, 12:14 PM
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cheers. how would i find out the size of my BB? I did some googling, and something came up saying 68mm/73mm.
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Old 05-10-12, 01:03 PM
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Your BB is most likely a 68 since it is a road bike.

Is this your crankset? I have little hands on experience with these but I think that little cap just covers things up. You need to tighten the allen bolt to hold the crank in place. Pics?

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Old 05-10-12, 01:21 PM
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I think he has an ISIS crank. Probably the cap that's messed up is the part that tightens the arm onto the spline. Once it's come loose under riding conditions, it's probably damaged both the crank and the spindle. Time for a new front end.
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Old 05-10-12, 02:07 PM
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Yes, he mentioned the crankarm came loose in the 1st post. What we don't know is how long he rode on it with the loose-crankarm. Any more than 1-2 minutes at most will result in the crankarm splines being destroyed. No amount of tightening the crankarm bolt/cap will fix that and there's no way to keep the bolt/cap tight once the crankarm is permanently buggered. At the very least, he needs a new crankarm and bolt/cap. The BB and spindle is most likely fine.
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Old 05-10-12, 02:57 PM
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Diagnosis: Wiggle drive-side crank arm, then wiggle the non-drive side crank arm. If one side wiggles slowly or is loose, but the other side is firm, then it's a loose crank arm. If both sides have perceptible play of equal amount, more than likely, the BB is loose.

First get familiar with how a BB assembly basically works: They are all similar in mechanical design principles. There is a heavy-duty, usually round, beefy, horizontal steel spindle in the middle that spins on two sets of bearings on either end of the bottom bracket shell. To fix the bearings against lateral movement into the frame of the bike, the assembly includes bored cups that are threaded tightly (usually in the US, drive-side is left-hand thread, non-drive side is right hand thread) into the shell into which the bearings fit, which then sandwiches the spindle precisely inside the BB shell. The spindle is LONGER than the BB shell, and the ends protrude from bored center holes of the threaded cups. The ends of the spindle are either notched or square-tapered. Right and left crank arms mount onto the ends of the spindle, and are then pressed and fixed onto the spindle using crank bolts ( or sometimes nuts if the spindle has threaded bolt ends rather than a tapped threaded hole - like a belly button that's an insey, or an outsey)

If both crank arms wiggle: Usually this means BB cups are not tight up against the spindle. The cups will need to be adjusted and re-tightened to torque spec. Usually on the drive-side, I use between 30 - 50 ft-lbs. On the non-drive side, with lock-ring style (traditional) BB, I use about 20 - 25 ft lbs. With newer cartridge BBs, I use 30 - 40 ft-lbs. To tighten the cups correctly, often requires removing the crank arms off of the spindle. You will need a crank arm extractor tool to do this. Note that drive-side cups are left-hand thread (lefty tightey, righty-loosey). non-drive side cups are threaded normally (i.e. righty-tighty, lefty-loosey).

If one crank arm has play and moves in a viscous way, then it may be damaged already or too loose. If the crank is not damaged too badly, you may be able to tighten the crank bolts tighter and reach the torque spec. Otherwise, you will need to replace the crank arm with something compatible (i.e. same length and supports same BB spindle end standard - e.g. JIS square taper, ISIS, Octalink, etc.) If you tighten the bolt to spec, and the crank still moves and wobbles, replace that crank arm.

If you cannot tighten the crank bolts either because of being stripped or deformed, then you may need to replace the spindle (if it's threads inside are damaged) or you may need to get new bolts. Bolts are either 8mm or 10mm allen or 14mm hex socket. You will need to tighten these to 20 - 25 ft lbs of torque or other spec according to your maker to prevent slippage and the crank arm from loosening and possibly getting damaged. Over tightening can also cause damage so you need to follow specs.
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Old 05-10-12, 04:44 PM
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Hi Thanks for the replies. The crank is the FSA Gossamer, shown in the image above (thanks Bianchigirll). So i've just checked and i was wrong it appears that the play was from the crank arm (left) coming loose again. I took the crank entirely off and found a lot of 'crud' or 'crap' between the spline and the edge of the bottom bracket. Possibly getting down there from when it initially came loose, preventing me from ever tightening it fully again? Iv'e removed most of this 'gunk' now. I Checked the play on the other crank arm and there was none even when the left crank was off, so i'm guessing the bottom bracket is tight? I could see no visible damage to the spline or 'splinal' grooves in the crank arm. DiabloScott/DannoXYZ, i did ride on it a while when it is loose i.e. miles, but i couldnt see and metal distortion or shavings. Bianchigirll there is no fastening method on the other crank that i could see. gyozadude Surely if iv'e damages the crank arm, i will have damaged the spindle (spline)?

thank you all very much. Unfortunately can't upload any pics at the moment as don't have a camera, can source one tommorow if still required. Good night
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Old 05-10-12, 05:35 PM
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Remember that this is a splined crankarm & BB-spindle, not the typical square-taper set-up that's most common out there. Those actually require at a minimum 25 lb*ft torque on the crankarm-bolt, and best to get 30-33 lb*ft, depending upon the model.

Yes, on the FSA, the right-side crankarm is permanently attached to the BB-spindle. If you wiggle the right-side crankarm in non-rotating radial direction (in-plane with frame, up/down, forward/back without rotating), and there's no play, the BB & bearings is OK. This is most likely the case.

Then when you wiggle the left-side crankarm in any direction and there's play, it's due to the loose interface between the splines of the crankarm and BB-spindle. You'll want to take the crankarm off completely and clean off all the debri from between the splines on the spindle and crankarm. Look closely for metal shavings and burrs. Remove these with jeweler's file.

When you re-install, here's a trick I've found that ensures the crankarm slides all the way into the splines properly:
1. insert a dime or other thin metal-scrap into the gap between the pinch-bolt ears of the left crankarm

2. insert pinch-bolts into the threaded side of the pinch ears

3. once the bolts contact the time, tighten them 1/4 a turn, this expands the clamp of the crankarm slightly

4. slide crankarm over BB-spindle as far as you can push by hand

5. apply blue Loctite 242 on end-cap/crankarm bolt and torque to 5 in*lb (+0.5/-1.0).

6. unscrew pinch-bolts and remove dime

7. apply blue Loctite 242 on pinch-bolts and re-install from non-threaded side.

8. screw in pinch-bolts until all excess threads have been removed, then alternate back and forth between them about 1/4 turn at a time until you achieve 103-114 in*lb torque.
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Old 05-11-12, 10:23 AM
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Yeah, ive removed the 'grime', and re applies the crank tightening everything up hard (i don't have a torqe wrench, so can't really do the dime method yet). I'll keep riding, and if it comes loose again, i will just by another crank arm, and get a shop to fit it. Does this sound logical. Thank you for all your help!
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Old 05-11-12, 11:41 AM
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Sure you can do that, and that's most likely what the last shop you took the bike to did as well.

The crankarm is most likely toast and the wiggle will return. It's highly critical on the very 1st installation that you torque the two pinch-bolts incrementally. And get their final torque evenly balanced as well. As with square-taper cranks, you pretty much have only ONE chance in the very beginning to install the crankarm correctly. Once it loosens and you ride on it for more than a minute, it's buggered permanently.

I've ridden miles one-legged with my left-foot resting on the chainstay to save a loose crankarm.
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Old 05-11-12, 12:13 PM
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I'm still not sure if he has an ISIS spline or external BB. First he said his "cap" was screwed up which sounds like an ISIS spline and the cap has the center allen bolts to tighten both sides of the crank on to the BB. Then he said it looks like the one Bianchi Girl posted - external BB with allen pinch bolts on the left, but Gossamer came in both versions so maybe he doesn't know what he's looking at.



The cap on the external BB version doesn't have anything to do with tightening the crank onto the BB and it wouldn't have anything to do with the crank arm coming loose. The cap and allen bolt on the ISIS system would.

Last edited by DiabloScott; 05-11-12 at 12:18 PM.
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Old 05-14-12, 12:33 PM
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Ok well if it comes loose i shall take it to someone to get the arm fitted, as sounds like i need a torque wrench. Diabloscott. The right crank arm looks exactly like bianchi girls picture. On the left arm you have the two pinch allen keys, however you also have a 'cap' thing which threads into the hollow protruding grooved thing from the BB which the splines fit into. If i were to loosen the pinch bolts the crank arm would theoretically not come loose as the cap acts to screw it tight to the frame. I.e. you put the crank arm on, thread in the cap, and as it tightens it pushes the crank towards the frame, the clamp/pinch bolts can then be tightened to secure it to the spline. however what hapens when it comes loose is the cap unscrews so the crank can come loose.

Thanks
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