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Old 02-18-04, 07:30 PM   #1
Portis
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Creaky Left Crank

I had a nice tailwind (25MPH) over a very bumpy gravel road today. It left me with a creaky left crank. I have tried to tighten the pedal and the noise is still there.

With both pedals horizontal and equal weight on my cranks i notice no noise. When I pedal forward i don't really notice the noise much. When I put the weight on the left pedal and pedal backwards i really hear the noise. I suspect that my crank arm is loose.

What tool can i go out and buy to give this a tightening. It has a hex type head but I don't know the size. My bike is a Trek 4300 if that helps. I am very sure that it is in the crank. How can i tell if it is loose other than just trying to tighten it?

Last edited by Portis; 02-18-04 at 09:25 PM.
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Old 02-18-04, 08:23 PM   #2
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The hex head may just be a threaded in crank bolt cover. It's probably an 8mm. Remove that to reveal a crank bolt or nut, which is either a 14mm or another 8mm hex head.
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Old 02-18-04, 10:57 PM   #3
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If it's more than just the tiniest bit loose, you should be able to tell by getting a firm grip on the right crank and trying to jiggle the left one. If the left crank can move independently of the spindle/right crank, it's loose. In which case you should tighten it before you ride the bike again because cranks can get worn down really quickly. If the nut DieselDan mentioned isn't an 8mm allen one, then you'll need either a socket or crank wrench to get to it.

If it's not your crank and you have lower-end pedals, it could be the bearings in your left pedal. I think these can sometimes be adjusted or overhauled, but I'm not sure of the specifics..
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Old 02-19-04, 09:45 AM   #4
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If the nut DieselDan mentioned isn't an 8mm allen one, then you'll need either a socket or crank wrench to get to it.
In the picture I attached, it looks to me like the "nut" is a lot bigger than 8mm. It is a little hard to see but it has a hex head and is the size you see in the picture. I will do your test to see if it is loose. I did wiggle it quite a bit and didn't see any play in it but i will try again.

Maybe it still is the pedal. I don't have a pedal wrench so it is hard to get it good and tight.
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Old 02-19-04, 01:56 PM   #5
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Originally Posted by Ranger
In the picture I attached, it looks to me like the "nut" is a lot bigger than 8mm. It is a little hard to see but it has a hex head and is the size you see in the picture. I will do your test to see if it is loose. I did wiggle it quite a bit and didn't see any play in it but i will try again.

Maybe it still is the pedal. I don't have a pedal wrench so it is hard to get it good and tight.

Guess I was wrong, it was an 8mm. Hauled bike down to LBS and he tightened it for free. (Also bought a pair of gloves)
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Old 07-14-04, 12:21 PM   #6
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Dragging this back up - is there a known design fault in the Trek 4300?

My left crank comes loose all the time, after repeated tightening and is beginning to p!ss me off. I got the LBS to replace the hex nut (I can verify that it is 8mm). I'm going to have to buy a real 8mm Allen key tool, as the 8 mil on my multi tool just isn't strong enough to tighten it as much as it needs (requires way more torque than a 3 inch plastic bodied Toolmanator can handle).

Any advice much appreciated.
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Old 07-14-04, 12:45 PM   #7
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Once it has loosened up, the square taper hole in the crank can be easily damaged by the rocking motion. The only solution is replacement of the crank, followed by proper torquing of the crank fixing bolt.
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Old 07-14-04, 01:33 PM   #8
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Quote:
Originally Posted by Alrocket
Dragging this back up - is there a known design fault in the Trek 4300?

My left crank comes loose all the time, after repeated tightening and is beginning to p!ss me off. I got the LBS to replace the hex nut (I can verify that it is 8mm). I'm going to have to buy a real 8mm Allen key tool, as the 8 mil on my multi tool just isn't strong enough to tighten it as much as it needs (requires way more torque than a 3 inch plastic bodied Toolmanator can handle).

Any advice much appreciated.
You're right. The torque spec for crankarm bolts is about 30 lb/ft. Imagine a 30 pound weight hanging off of the end of a foot long allen wrench. You'll have difficulty generating anything close to that much torque with a folding allen wrench set.

The bad news is that, if your arm keeps loosening up, that means that it's hosed. If you aren't too particular about your crankarms matching perfectly, an LBS should be able to get you a replacement for around $15.00 or $20.00. For some reason that I can only guess at, this seems to be a problem that is more common with left crankarms than right crankarms.
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Old 07-14-04, 02:14 PM   #9
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Bike is 8 weeks old - LBS will replace it (or deal with a very angry me). You reckon it's definitely the crank arm?
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Old 07-14-04, 02:18 PM   #10
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If the crank keeps loosening up, and the shop has already replaced the fixing bolt, my guess would be that the square taper hole is no longer the right size and shape. It probably came loose the first time from inproper assembly, and got buggered up that first time. That is why it will no longer stay tight. I would take it back and quietly (at first) ask them to replace the crank. Escalate volume and intensity as necessary.
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Old 07-14-04, 02:52 PM   #11
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Quote:
Originally Posted by Alrocket
Bike is 8 weeks old - LBS will replace it (or deal with a very angry me). You reckon it's definitely the crank arm?
I can't say for 100%, but it's a common problem. Every shop owner that I've talked with has had a left crankarm come off during a test ride at least once.

When that happened in my shop, I'd hand the torque wrench to my newest bike assembler and told him to check every crankarm in the shop. Trust me, I only had to do that once.
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Old 07-14-04, 02:55 PM   #12
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If the bike is that young, it could only be as loose as you found it to be as a result of it never having been torqued down properly. This is exactly what warranty protection is for. A one-year warranty may seem short to many, but my limited personal experience and slightly less limited (I hope, anyway) common sense tell me that the bulk of problems like this arise very early on, and are usually related either to manufacture or assembly.
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Old 07-14-04, 03:08 PM   #13
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Originally Posted by madpogue
If the bike is that young, it could only be as loose as you found it to be as a result of it never having been torqued down properly. This is exactly what warranty protection is for. A one-year warranty may seem short to many, but my limited personal experience and slightly less limited (I hope, anyway) common sense tell me that the bulk of problems like this arise very early on, and are usually related either to manufacture or assembly.

Actually, if it's a creak and you have a sealed bottom bracket I would suggest checking the left and right hand arm and tighten if needed. If it still creaks, take it to the shop and have them check the bottom bracket cups. In the sealed units, a creak can occur as a result of the metal to metal contact between the cups and the bottom bracket shell. In my shop experience, generally, pedals made "clicking" sounds, loose sealed bottom brackets made "creaking" sounds. Most "creaking sounds" were related to bottom bracket problems. Generally, a loose crank arm would continue to became worse over a short period of time to the point that you couldn't help but notice it, especially when it eventually falls off...
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