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Novice wanting to know about crank arm compatabiliy.

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Novice wanting to know about crank arm compatabiliy.

Old 06-24-13, 04:30 PM
  #1  
jsidney
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Novice wanting to know about crank arm compatabiliy.

This is an older bike. 1985 Trek 520.

I am needing a left crank arm that will work with a Sakae CR. I cannot find a Sakae CR left crank arm and I don't know if I can just pop something else on there in it's place. This is not a permanent fix, I will be getting the group changed out later on.

I really don't know much but since it is on the left side I didn't see why I couldn't just put any old 170mm crank arm on there.
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Old 06-24-13, 04:40 PM
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As long as it fits, and is the same length as the other side, you should be good to go. Especially if it's just temporary. I think I've read before that it's left arms that more commonly fail (which would explain why you're looking for a left). fleaBay has a bunch for $13 delivered, seems the cheapest are square-taper, which I'm guessing is what you're looking at from 1985.

Also, for purists, if you're working with Sakae, that's Japanese, which should have a JIS square-taper BB, which is the shorter kind. If you happen to try a left crank of the other square-taper standard, (ISO I think it's called, taper-angle is the same, but it's longer), then your BB would work, but the square taper would not go as far into the crank. Some purists would complain, but for temporary use you can't go wrong. (If it was the other way around, if you had ISO sq-taper BB, and you tried to put a JIS crank on it, it wouldn't fit; the end of the spindle would bottom out before you started pressing the crank onto the taper, if that makes sense).
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Old 06-24-13, 04:43 PM
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Oh, and take care that you buy a crank with the square-taper in the right orientation. They come at least two ways; relative to the crankarm, the square-taper hole could look "square", or it could look "diamond".
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Old 06-24-13, 04:44 PM
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jsidney
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Originally Posted by RubeRad View Post
As long as it fits, and is the same length as the other side, you should be good to go. Especially if it's just temporary. I think I've read before that it's left arms that more commonly fail (which would explain why you're looking for a left). fleaBay has a bunch for $13 delivered, seems the cheapest are square-taper, which I'm guessing is what you're looking at from 1985.

Also, for purists, if you're working with Sakae, that's Japanese, which should have a JIS square-taper BB, which is the shorter kind. If you happen to try a left crank of the other square-taper standard, (ISO I think it's called, taper-angle is the same, but it's longer), then your BB would work, but the square taper would not go as far into the crank. Some purists would complain, but for temporary use you can't go wrong. (If it was the other way around, if you had ISO sq-taper BB, and you tried to put a JIS crank on it, it wouldn't fit; the end of the spindle would bottom out before you started pressing the crank onto the taper, if that makes sense).
Thanks fore the info.
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Old 06-24-13, 04:48 PM
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If you are replacing the arm because the pedal threads are stripped, you should be aware that they can be economically repaired with a Helicoil insert.
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Old 06-24-13, 04:50 PM
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Originally Posted by RubeRad View Post
Oh, and take care that you buy a crank with the square-taper in the right orientation. They come at least two ways; relative to the crankarm, the square-taper hole could look "square", or it could look "diamond".
I didn't think about that. Thanks for warning me.

https://img.cla*****.com/883/722161/1...jpg?1370466087
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Old 06-24-13, 04:57 PM
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Originally Posted by jsidney View Post
I didn't think about that. Thanks for warning me.

https://img.cla*****.com/883/722161/1...jpg?1370466087
That pic I would call "diamond". I think that is more common.

And dsbrantjr is right, stripped pedal eyes can be repaired with helicoil by most well-equipped shops, but if the crank is not special, and soon to be replaced, it might not be worth it. I had it done once to save a crankset which was special to me because I got it from my dad, so it was worth it at $40 (although others at BF seem to say the going rate is closer to $20). Your choice of course.
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Old 06-24-13, 04:58 PM
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Originally Posted by RubeRad View Post
That pic I would call "diamond". I think that is more common.

And dsbrantjr is right, stripped pedal eyes can be repaired with helicoil by most well-equipped shops, but if the crank is not special, and soon to be replaced, it might not be worth it. I had it done once to save a crankset which was special to me because I got it from my dad, so it was worth it at $40 (although others at BF seem to say the going rate is closer to $20). Your choice of course.
My problem is there are not shops any where near me.
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Old 06-24-13, 05:28 PM
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Originally Posted by jsidney View Post
My problem is there are not shops any where near me.
Then your choice is clear! Quit your day job and start a bike shop!

And meanwhile, order a crank for $12.95 from fleaBay.
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Old 06-24-13, 06:04 PM
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Originally Posted by RubeRad View Post
Then your choice is clear! Quit your day job and start a bike shop!

And meanwhile, order a crank for $12.95 from fleaBay.
I have one ordered. I don't think a bike shop will last long in this area. Not enough population in the county.
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Old 06-24-13, 06:56 PM
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Other thing is Q-factor - how far away from the bike's centerline does the crankarm sit - basically how far does it flare out. This isn't as important as the other concerns though. As long as you've matched diamond orientation, JIS taper, and 170mm length, those are the more-important things.
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