Cotter Cranks - Replacement parts
 

Hello All,

I have been working on a late 60's Atala. It has cottered cranks with a bent spider arm and likely bent chain rings as well. I was looking to find a replacement part for these. Are there any sizing/compatibility issues to be aware of when finding a replacement cottered crank? I am guessing that cotter pin size and pedal thread could play a part? Is there anything else to look out for?

While I would love to change this over to a square taper, I want to keep the vintage look without a sizable investment.

Welcome to the forum Flume,

Readers will be able to assist you better with work on your Atala if you can post some images of the bike and the spots where you have questions.

Out of alignment spider arms and chainwheels can often be put right with a LaJeunesse straightener or similar homemade tool:

http://www.avantbicyclesupply.com/wp...00-510x166.jpg

Jim Langley's Bicycle Beat: Q&A: Straightening Bent Chainrings & Finessing Your Shifting

I try this with lesser bikes. Couple of well placed hardwood blocks and clamps. Bam.

http://www.expert-toolstore.com/2461...mer-mallet.jpg

:thumb:

Sometimes me auld joints feel like they might benefit from a wee kosh with a deadblow. :D

Aye laddie, aye and delivering a few can be therapeutic as well. ;)

Stay away from the French as they will be incompatible with your spindle and your pedals.

Obviously another Italian crank arm will work. Although I have recently found quite a few prewar 3-arm cranks have a 99mm BCD, which is obviously different from the postwar 116mm BCD standard. SO double check before purchase.

A British crank should be fine on an Italian spindle. Pedals work both ways between the Italians and Brits.

Chances are that you will be just fine with your present components which will require a wee bit of TLC, coupled with a bit of understanding (read the whole procedure before starting to do the repair) and elbow grease...

Using one of my Legnano Grand Premio bicycles as an example, this is how I deal with bent spider arms and bent chain rings...

http://www.mytenspeeds.com/My_TenSpe..._Comment_1.jpg

Thanks for the replies all. I will give repair a go, appreciate the detail on your site Randyjawa. I had made a short lived attempt to true the spider arm in a bench vise, but having the crank back on the bike would make it much easier to gauge progress.

Also good to know to stay away from French crank arms if I get carried away with the crow bar.

One check you might wish to make prior to any straightening would be to verify the straightness of the bottom bracket spindle.

A simple test is to remove the right hand crank arm and hold the tip of a screwdriver or similar up next to the end of the spindle as you slowly rotate it.

In my workshop made a jig for straightening the spiders and chainwheels of cottered steel cranks by cutting up a dead frame and fitting it with a cottered bottom bracket. The dead frame/jig can be put into the repair stand and any cottered steel cranks which come into the shop loose and be checked and aligned it need be. Such a tool would be pointless for most home mechanics as they can just do the work on the bike itself. In my case went through a great many cottered steel crankesets over the years...