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Old 04-07-11, 11:35 AM   #1
audrey5432
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Ill Fitting Left Crank Arm

My husband received a 26" Men's Safari from his job. (brand new) After riding it for less than an hour the left crank arm fell off. The nut holding it in place was stripped. (He brought it back home) Upon inspection the left crank arm would not fit fully on the axle. (When I looked on the inside I could see irregular groves. Here is a picture of the section of the crank arm that has the groves; sorry groves cannot be seen in photo.)


We called the company and after shipping us the wrong part, twice, they sent us another new bike.

Here is a picture of the "new" new bike's problem area:


There is a noticeable gap (~1/2") between the left crank arm and the bottom bracket.

Is this a defect in manufacturing/design error or just the way some bikes are? My fear is that if he rides the bike the same problem will reoccur.
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Old 04-07-11, 02:55 PM   #2
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Originally Posted by audrey5432 View Post
There is a noticeable gap (~1/2") between the left crank arm and the bottom bracket.

Is this a defect in manufacturing/design error or just the way some bikes are? My fear is that if he rides the bike the same problem will reoccur.
Are the pedals about equidistant from the seat tube? If so, the 1/2 inch gap is normal.

The "defect" on the first bike is that the left crank arm wasn't bolted on tight enough. Riding the bike with the crank arm loose then damaged the parts.
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Old 04-07-11, 03:05 PM   #3
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Are the pedals about equidistant from the seat tube? If so, the 1/2 inch gap is normal.
No, the left is significantly further away. even when concidering the gears on the right side.

Edited for spelling error

Last edited by audrey5432; 04-07-11 at 03:06 PM. Reason: spelling error.
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Old 04-07-11, 03:15 PM   #4
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No, the left is significantly further away. even when concidering the gears on the right side.
I wasn't asking about the bottom bracket end of the crank arm. Let me rephrase: Are the pedals centered on the bike? Does the rider have to place their right foot snug up against the frame while stretching their left foot way to the outside?

If the pedals are indeed off center, then look at the spindle (ie "axle") where the left crank arm mounts. How much of the square portion is visible? You shouldn't see much of the square taper portion.

Alternately, super tighten the bolt/nut that attaches the left crank arm. The spec is "Oh my gosh" tight.
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Old 04-07-11, 03:22 PM   #5
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I was looking at the pedals. 3/8" inch of the taper is visable. As to the bolt/nut: it is so tight I cannot move it at all.
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Old 04-08-11, 06:18 PM   #6
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The required torque on the nut/bolt that attaches the crankarm is about 27-33 lb*ft. The only way to achieve this amount of torque is with an automotive-style ratchet wrench with 12" handle. Park Tool makes a stupid 6" wrench with 14/15mm sockets to use for crankarm bolts. There's simply no way to achieve the required amount of torque with that wrench.

The distance you want to inspect is the distance between the back of the crankarm where the pedal attaches and the chainstay. Inspect one side, then spin the cranks 180-degrees and inspect the other side. They should be pretty close to identical although slight variation of up to about 1/8" between the two sides should be fine.

Even if you're shipped a bike completely assembled, it would be good practice to disassemble it, grease all the bearings and re-assemble paying attention to all the fasterner's torque values. The following are serious safety areas that should not be ignored (can really turn into life-or-death scenario) :

- brake-lever clamps
- handlebar clamps at the stem
- stem clamp at the fork
- crankarm bolts
- wheel-nuts or QR skewers (flip the lever, not spin it)
- brake-cable fixing-bolt (too loose and the cable slips, too tight and the cable snaps)
- spoke-tension on wheels

Here's a list of torque-values for the various fasteners on a bike: Park Tool - recommended torque

Also do a search on here for "loose crankarm".

Last edited by DannoXYZ; 04-08-11 at 06:23 PM.
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Old 04-08-11, 06:25 PM   #7
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The crank arms were attatched at the factory, so I assume they were done to specs. (at least I hope they were)

I had a friend come by. He measured it exactly the way you just stated and the left is 3/8" further away. He found this number interesting. Later after he went home he measured his own bike. His is also 3/8" different. (but with his the one that is further away was the side with the gears.)

I plan to have my husband ride the bike next week and see if the left crank arm falls off like the other bike. If it does, I'm going to get my money back.

Thank you all for your help.
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Old 04-08-11, 07:12 PM   #8
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bicycles need professional/proper assembly. everything is pretty much not up to spec
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Old 04-09-11, 12:02 AM   #9
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Originally Posted by audrey5432 View Post
The crank arms were attatched at the factory, so I assume they were done to specs. (at least I hope they were)

I had a friend come by. He measured it exactly the way you just stated and the left is 3/8" further away. He found this number interesting. Later after he went home he measured his own bike. His is also 3/8" different. (but with his the one that is further away was the side with the gears.)
It very well could be that the bottom-bracket spindle was installed backwards. Not uncommon in mass-assembly operations.
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