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Old 2005-04-05, 05:52 AM   #1
markf
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need some new cranks

well, i need some new cranks. i've got my new hub picked out, now i need some new cranks. i'd like to go longer than 150mm, but don't want to spend the cash for the black widows. what's the best crank i can get for square taper and under $50? the 170mm Dotek's on UDC for $25 seem alright, but are they strong? will they hold up to serious muni abuse?


should mention i'm coming from 152mm Nimbus X cranks, which would've been fine but i didn't keep them tight enough. D'oh.
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Old 2005-04-05, 05:57 AM   #2
jagur
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Re: need some new cranks

Quote:
Originally posted by markf

should mention i'm coming from 152mm Nimbus X cranks, which would've been fine but i didn't keep them tight enough. D'oh.
what hub are you using? my nimbus X 127's havent ever come loose on a UDC hub.. are you greasing the tapers so they go on farther?

BTW, i found Kooka's on ebay for 68 bucks... look there you might get lucky.
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Last edited by jagur; 2005-04-05 at 05:58 AM.
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Old 2005-04-05, 06:32 AM   #3
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The Sugino tandem cranks are an option. I don't know how they compare with the Dotek cranks. My gut feeling is that the Sugino cranks are better but I have no testing or data to back that up. Here's a thread on the Sugino cranks and where you can order them: Sugino crank thread.

With any aluminum crank you need to make sure the cranks are installed correctly the first time. You don't always get a second chance with aluminum cranks. Put a little grease on the tapers, put some Red Loctite in the bolt/nut threads/ then use a torque wrench to tighten them to 35 or 40 foot-pounds. That should do it. If they are tight enough at the start and Loctited then they should stay tight for a long time.
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Old 2005-04-05, 08:06 AM   #4
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i neglected the locktite. thought if i kept an eye on them i'd be fine. turns out i don't have that sharp of eye, or i suck, either way i need some new ones. I'll be using a suzue hub, and the unicycle.com hub is too wide for my gb4 muni frame. there's a 3-4 year old suzue hub in there now and i'm trying to keep this semi-cheap so i can afford to drop some cash on a nice trials uni, as i think doing trials-y things on my muni is the single biggest reason i broke stuff. but thanks for the ideas.
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Old 2005-04-05, 10:03 AM   #5
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I think the Loctite is an important step. Here's what I think happens with the standard square taper cranks. It's just a thought experiment. No real analysis to back it up.

When you put a lot of force on the crank (landing a drop or just pedaling hard) the crank will want to squirm up the taper a bit. Then when you take that force away the crank wants to go back to where it was. So the tapered interface goes through a lot of cycles of the crank being pushed up the taper and then going back down.

This squirming on the taper will be more pronounced with aluminum cranks than steel cranks because aluminum is softer than steel which means an aluminum crank can be forced further up the taper. Then there are different grades of aluminum alloy. The common 6061-T6 is softer and not as strong as some of the 7000 series alloys like 7075-T6.

The better and more expensive aluminum alloy cranks are made from the 7000 series aluminum. The less expensive alloy cranks are made from the 6000 series aluminum. The Odyssey Black Widows are made from 7075-T6. The Kookas are made from a 7000 series alloy but I'm not sure exactly which. One source said they're made from 7075-T6.

The cranks made from 7000 series aluminum are going to squirm less on the taper with all other things being equal (quality of the machining on the taper, etc.). That could explain why better quality cranks, like the Kookas, stay tight longer than lesser cranks made from lesser aluminum.

So the crank squirms up the taper under load. When that happens there is less force pushing back on the crank retaining bolt/nut so the retaining bolt/nut has an opportunity to loosen up just a bit. Do that over and over and over and over and eventually the retaining bolt/nut can get loose enough to allow the crank to flop around.

My theory with the Loctite is that the Loctite will keep the retaining bolt/nut from loosening up if it's given the opportunity.

The other important part is to get the retaining bolt/nut tight enough to begin with. That's the reason for the torque wrench. So lets say that the crank squirms up the taper but since the retaining nut is so tight that it continues to push against the crank. There is never a gap created between the crank and the retaining nut and no opportunity for the retaining bolt/nut to loosen. The Loctite is there to make sure it stays tight. You take the force off the crank and the crank returns back to where it was and everything is still tight and the retaining nut hasn't moved.

Just a theory. But it explains why the retaining nut needs to be so tight and why the Loctite may be helpful. It also explains why aluminum cranks can be harder to keep tight than steel cranks.
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