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Crank Arm Replacement

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Crank Arm Replacement

Old 12-15-15, 10:48 AM
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Paul J 
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Crank Arm Replacement

Last week I had mentioned that on a long climb our granny chain ring had worked loose and I wasn't able to tighten it on the road. Thursday evening I went to my LBS and we took the crank off and found the threads stripped with no hope of salvaging using longer bolts or something. First thing Saturday morning I talked with Tandems East and was able to drive over and pick-up a replacement Race Face triple 170 crank arm. Back to the LBS and we were able to bring the rings across after replacing the mangled granny and had us on the road to take advantage of the 65 degree weather this past weekend. Mel was gone but we were able to figure things out with his guys over the phone.

I always love going to Tandems East and look at all the bikes he has on hand, from a used Trek or Sterling to new Cannondales, Co-Motions, Calfees and Sevens. It's a two-hour drive but worth it every time.

One fun thing, my LBS has a small machine shop and he is trying to salvage the original crank arm.
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Old 12-19-15, 06:01 AM
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A Helicoil insert should work if there's enough meat on the spider. Takes about 5 minutes to drill-out, tap and install one.
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Old 12-19-15, 08:48 PM
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The shop wasn't able to find a helicoil so is machining an insert. He's just having fun with it in know.
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Old 01-06-16, 06:20 PM
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Not to take over your thread, but it is an appropriate place for my question. Is there any reason why a stoker crank couldn't be a 165, and the captain's crank a 175? Or do they have to be the same size? My wife is just a little too small for ours realistically, and I was just thinking earlier today about maybe making the switch.
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Old 01-06-16, 06:32 PM
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Originally Posted by LuckySailor View Post
Not to take over your thread, but it is an appropriate place for my question. Is there any reason why a stoker crank couldn't be a 165, and the captain's crank a 175? Or do they have to be the same size? My wife is just a little too small for ours realistically, and I was just thinking earlier today about maybe making the switch.
No reason they have to be the same and it's not that uncommon to have them vary. In addition to leg length differences, a change in crank length can also compensate for variations in preferred cadence. Switching to a shorter crank tends to result in an increased cadence. If the captain prefers a higher cadence than the stoker when both have equal crank lengths then putting on a longer crank for the captain can help to reduce his preferred cadence so they are better matched.
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Old 01-06-16, 11:27 PM
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I run a 175 front, 170 rear and about 140 mid position on a triplet. No reason not to have differing lengths depending on rider. Crank arm shorteners are also a choice, but are likely to be less than the 165 that you mentioned. The shorter crank arm also makes it so that the seat does not have to be lowered as far, or allows a shorter rider to ride on the back if the saddle is at the bottom of its possible height.
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Old 01-07-16, 06:43 PM
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Originally Posted by LuckySailor View Post
Not to take over your thread, but it is an appropriate place for my question. Is there any reason why a stoker crank couldn't be a 165, and the captain's crank a 175? Or do they have to be the same size? My wife is just a little too small for ours realistically, and I was just thinking earlier today about maybe making the switch.
No problem at all. We ride 175 for me in front and my wife uses 170 in he stoker position. It's the same r.p.m. Just bigger circles in front. I have very long legs hers are much shorter.
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