Bicycle Mechanics - Replacing cottered crank?
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07-09-08, 12:49 PM
I have what may be a very ignorant question. I have an old Motobecane and I would like to replace the crank, however the bottom bracket seems just fine. Am I going to have trouble finding a new crank on? If so, what do I need to look for?
07-09-08, 01:51 PM
You'll need to replace the spindle.
IF you stick to sq. taper, you could probably reuse your existing cups and avoid the expense/hassle of finding a replacement BB. (is it French or....? problems)
Loose screws sells a spindle that could probably work. It's "offset", so if you used the "short" end on the DS side, it would probably work, although chainline might not be ideal....Probably too far out.
I might be doing a similar swap in the future, making my brothers early 70's Asian 10 speed into a 15 speed.
Else, things get more expensive.
07-09-08, 03:04 PM
If the crank is functional, I would just leave it. Any cottered crank Moto was not a high end bike, so no point in upgrading.
Cottered cranks are a pain to remove. I would just pour about 2 tablespoons of oil down the seat tube a couple of times a year to keep the BB lubricated and just ride it.
07-09-08, 11:38 PM
I would take it to a bike shop and have the axle measured. I was able to remove the crank cotters via Sheldon's SFH and pipe method. I tried using a press and didn't find the results I needed. Or just take the whole bike in and have them do it. They should be able to get square taper axles in the length you need - they come in many sizes from looking at the catalog. I also changed out my BB as the old one was hashed; the new one had deeper cups I guess for better adjustment. Mine is an old Hercules with 70mm BB width.
See Sheldon Brown's site regarding French bicycles LINK (http://www.sheldonbrown.com/velos.html). On a strictly economic basis, it may not be justifiable but he does list (and Harris Cycle apparently carries) the Sugino spindles you would need LINK (http://sheldonbrown.com/harris/french-cranks.html#bottom). Or stay with the cottered cranks and get new cotter pins from Harris (further down the page at the previous link). Also see his page on cottered cranks LINK (http://sheldonbrown.com/cotters.html).
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