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Swapping Crank arms on Square taper?

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Swapping Crank arms on Square taper?

Old 01-05-09, 12:02 AM
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Swapping Crank arms on Square taper?

I've read that it isn't a good idea to swap crank arms on square taper cranks.

Is this true?

I would be swapping cranks a few times a year and was wondering if my cranks/crank arms would get damaged.

Thanks!
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Old 01-05-09, 12:04 AM
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Yes, the square taper may get a bit worn. Doing it a few times a year shouldnt be a problem. If you start to feel looseness, just replace the BB. Square taper BB's can be found anywhere. Yesterday I put a quarter into the machine for a Diet Coke and it gave me a Square taper BB.
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Old 01-05-09, 05:02 AM
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No its not a great idea to take square taper cranks on and off often as they do wear which will start it creaking.

Many years ago I use the same cranks for road and track racing with different rings and was therefore dismantling it several times a year. It didn't fail on me but it did start creaking.

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Old 01-05-09, 05:04 AM
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Originally Posted by cedricbosch
Yes, the square taper may get a bit worn. Doing it a few times a year shouldnt be a problem. If you start to feel looseness, just replace the BB. Square taper BB's can be found anywhere. Yesterday I put a quarter into the machine for a Diet Coke and it gave me a Square taper BB.
Actually, since the spindle is hardened steel and the crank arm is soft alloy, the wear takes place in the square hole of the crank arm, not on the spindle. So replacing the BB will not remedy the problem once the interface becomes sloppy.
Once the crank arm hole is too large to get a good tight press-fit when mounted on the spindle, you need to replace the crank arm(s).

Last edited by simplify; 01-05-09 at 05:06 AM. Reason: to include quote
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Old 01-05-09, 05:27 AM
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For the purposes you're talking about, if you take care and use something like Loctite 243 to dress the BB spindle, you should have few problems. The Loctite will help prevent creaking. It's no different to taking down a ball-and-race BB for servicing every six months or so. It's reasonable to get a torque wrench and tighten the crank bolts to their specified tightness.

If your left crank starts to wobble while riding even after you've tightened, then it's cactus. The right one is less likely to wobble because the forces are a little different thanks to the chain, and the crank is actually trying to tighten the crankbolt as you pedal.

So in the end it's the square taper on the left crank that you need take really good care of.

Hope this helps. Or not.
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Old 01-05-09, 03:26 PM
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Originally Posted by cedricbosch
Yesterday I put a quarter into the machine for a Diet Coke and it gave me a Square taper BB.
That's because you can't get a Coke for a quarter anymore
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Old 01-05-09, 05:22 PM
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so...

where can I find single crankarms?

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Old 01-05-09, 06:01 PM
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Originally Posted by subframe
so...

where can I find single crankarms?

jenson catalog, lbs, coke machine
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Old 01-05-09, 06:39 PM
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Originally Posted by subframe
so...

where can I find single crankarms?

Eharmony???
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Old 01-05-09, 06:42 PM
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Originally Posted by DannoXYZ
oh, if only...
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Old 01-05-09, 06:45 PM
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A few times a year should be any problem. I've done that for quite some time to clean stuff or to swap frames.

As long as you don't ride it loose and you have a JIS BB with a JIS crank (for example) you should have no problems.

Torquing to spec is a good idea and loctite the bolts (I use 222).
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Old 01-05-09, 07:37 PM
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once you place the crank arm on for the first time (and as mentioned^^^ it has to be the same taper) after tightening to the corretc toruqe spec you should remove the crankbolt and there should be approx 3mm from the end of the bb spindle to the flat taper of the crank arm.

the crank arm is actually deforming and stretching to fit over the bb spindle. as the alu crank arm is more pliable. if you remove them and reinstall, it will stretch it again. After enough times it will enlarge and the end of the spindle will almost be or will be flush with the alu crank arm seat. Then it will loosen and basicly be useless. If the crank arm loosens while riding you really need to tighten it straight away or the taper faces on the crank amr will be damaged.

Always tighten the crank arms onto the spindle using the steel crank bolts then if you wish you can remove them and install lighter bolts.

you do not grease or lubricate the taper surface, but you must grease the spindle thread well.

A few times a year would be ok I guess, just don't over toruqe it to prolong the life of the components.
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Old 01-05-09, 08:20 PM
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What I've noticed in some cases, is that the tip of the spindle will actually gouge out some material from the crankarm. Repeated installations makes the square hole in the arm larger and larger. Each time, it pushes the arm further and further up until the tip of the spindle will bottom out on the bolt and no more tension is possible. The arm then wobbles slightly.
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