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Old 01-05-10, 07:43 PM   #1
ddot
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Loose crank arm -- Is it a bad sign?

'Allo folks. Went for a ride this evening and noticed my non-drivetrain crank arm had some play. I de-saddled and examined closer: the crank arm plays and moves 1/4 of an inch away from the frame. The other arm is not loose at all.

I took the cap off and saw a rusty (and loose) crank bolt. I finger-tightened it and rode home.

My questions:

1. Is this an imminent sign of my bottom bracket dying? It could be the original -- it's a 70's Italvega.
2. I have some tools coming in at the end of the week and will be able to re-tighten it. After finger-tightening it, there was still play. Bad sign?
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Old 01-05-10, 07:54 PM   #2
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Bad for your crank arm. Says nothing about the BB - if your right crank doesn't have play, it's fine.

But get that crank bolt tightened up ASAP. Finger-tightening it won't be anywhere near enough to prevent further damage to your crank arm, which may already require replacing...

But generally they can handle being mashed a bit, so you should be okay... just don't wait till the end of the week to tighten it; borrow a tool to do it, or don't ride it.
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Old 01-05-10, 08:05 PM   #3
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The bb spindle is probably a much harder material than the crank arm, so the crank arm will likely deform before the bb spindle would. Hard to say how early you've caught on, though, but how long has it been since you pulled the cranks and checked the bb out anyways? Finger tight is nothing to a crank arm bolt, usually needs to be tightened in the range of 300-435 in-lbs torque.
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Old 01-05-10, 08:08 PM   #4
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+1 Do NOT ride it if there's any play of the crank on the spindle. This connection depends on the square hole in the crank being a good match to the square taper end of the spindle. Once it's loose there's a good chance that the hole in the softer Al crank gets distorted by movement against the steel spindle. So it may already be too late to save the crank, but it almost certainly will be if you continue to ride before tightening it properly
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Old 01-05-10, 09:04 PM   #5
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Hard to say how early you've caught on, though, but how long has it been since you pulled the cranks and checked the bb out anyways?
Never have before, nor do I know what to look for.
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Old 01-05-10, 09:05 PM   #6
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Not that this hasn't already been said, but simply to emphasize, your bottom bracket is ok, but your crank arm is in imminent danger. With the bolt loose, it is quite likely the steel bottom bracket spindle will wear away at the taper of the crank arm, leaving it useless. Tighten it down properly as soon as you can.

Bad news is, it might already be dead, but it's worth a check.
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Old 01-05-10, 09:05 PM   #7
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So it may already be too late to save the crank, but it almost certainly will be if you continue to ride before tightening it properly
If I unscrew the bolt, is there a way to check if the crank arm is beyond use?
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Old 01-05-10, 09:08 PM   #8
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Bad news is, it might already be dead, but it's worth a check.
I just felt the looseness on my 5 minute ride around the block this evening. Is it possible that it has been wearing down before I noticed it?
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Old 01-05-10, 09:11 PM   #9
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If you only just noticed it, your crank is prolly still good.
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Old 01-05-10, 09:26 PM   #10
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Some guys are just oblivious to stuff like that, hard to tell over the internet...
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Old 01-05-10, 09:33 PM   #11
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If I unscrew the bolt, is there a way to check if the crank arm is beyond use?
It's easy.

Tighten the arm back up to torque spec and if it comes loose again it's beyond use.
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Old 01-05-10, 10:15 PM   #12
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^^^ +1 ^^^
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Old 01-05-10, 10:43 PM   #13
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Tighten the arm back up to torque spec and if it comes loose again it's beyond use.
The set of wrenches I ordered are Stanley triangle, handheld wrenches. Will that be enough torque?
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Old 01-05-10, 10:57 PM   #14
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The set of wrenches I ordered are Stanley triangle, handheld wrenches. Will that be enough torque?
I'll try and save you operators irate reply, but a torque wrench that accurately measures torque will properly install a crank bolt.

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Old 01-05-10, 11:08 PM   #15
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In the absence of a torque wrench, do it up pretty bloody hard.
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Old 01-05-10, 11:22 PM   #16
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torque wrench vise grips huh? haha. Is that so you can tell how much torque it took to remove it?
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Old 01-06-10, 11:20 AM   #17
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It's easy.

Tighten the arm back up to torque spec and if it comes loose again it's beyond use.
Yup, and the torque spec is generally around 30 or 35 lb/ft. For reference, imagine a 30 lb weight hanging off the end of a foot long wrench. That's more than I would probably use if left to my own judgement and definitely more than you are likely to generate using a 6" long allen wrench.
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Old 01-06-10, 03:56 PM   #18
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Yup, and the torque spec is generally around 30 or 35 lb/ft. For reference, imagine a 30 lb weight hanging off the end of a foot long wrench. That's more than I would probably use if left to my own judgement and definitely more than you are likely to generate using a 6" long allen wrench.
Do you think I'll be able to generate that amount of torque with these Stanley tools?


This whole discussion is making me a little nervous about working on my bike. I don't own (or planned on buying anytime soon) a torque wrench set. Could I buy a torque wrench and use my Stanley sockets?
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Old 01-06-10, 05:04 PM   #19
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It would be extremely difficult to get the correct torque with that set.
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Old 01-06-10, 05:29 PM   #20
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A torque wrench isn't really nessicary but you can overtighten your crank arm which is bad for it too, you might think about taking it to your LBS.
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Old 01-06-10, 05:40 PM   #21
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For that vintage of bike, I assume you have either hex nuts or hex-head bolts to hold the crank arms on. You'll need the correct sized socket in 3/8" drive to attach it to a torque wrench (not sure if your set is square drive or something else). Harbor Freight sells a decent 3/8" torque wrench for less than $20 and a set of metric sockets for $10.
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Old 01-06-10, 06:59 PM   #22
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For that vintage of bike, I assume you have either hex nuts or hex-head bolts to hold the crank arms on. You'll need the correct sized socket in 3/8" drive to attach it to a torque wrench (not sure if your set is square drive or something else). Harbor Freight sells a decent 3/8" torque wrench for less than $20 and a set of metric sockets for $10.
After looking through my dad's 6-point squre drive sockets, I think I need a 14mm. However, the torque wrench he had at the house didn't fit the drive of the sockets.
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Old 01-06-10, 07:21 PM   #23
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don't worry about the torque wrench. Just do it up as tightly as you can and you'll probably be fine. As said before, if it comes off again you should replace it.
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Old 01-06-10, 10:38 PM   #24
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Just do it up as tightly as you can
Depending on how big you are, of course... do it up as tight as a little feller could.
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Old 01-07-10, 07:52 AM   #25
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Since the problem appears to be just the left side, replacement is easy and fairly inexpensive, if the OEM parts aren't too important to you.
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