mikennett

I bought an older model Motobacane Mirage, I'm guessing mid 1970s, and converted it to fixed gear. Now two years later one of the cranks is loose and I have been told by the local mechanic that its because the cranks were switched at some point prior to my purchase, that they are not the original parts, and they are for a reason not entirely clear to me(something to do with an odd pin size?) unfixable.

The mechanic tells me that I might require an entirely new bottom bracket which could cost anywhere between $100 and $300 dollars, and considering I made the bike for about $100 I'm not too keen on this idea. And for the privalege of knowing how extensive the damage is, I'll have to pay him. He did also recommended that I search for used replacement parts but thus far my efforts on ebay and craigslist have failed.

Does anyone know where I could find a full crank set, including a bottom bracket, for a old Motobacane Mirage? Or have any other suggestions for another potential solution? I live in NYC if that helps. Thanks in advance.

mparker326

Can you post a picture of your crankset and let us know which crank arm is loose? Does it have cotters or is it a 3 piece crank?

If it has cotters, and is loose, you would just need a new cotter in the correct size.

If it doesn't have cotters, you should be able to replace the crank that is loose. Usually it is the left crank that is loose. If that is the case, you don't have to worry about chainline if you replace the arm.

I'm not sure why you would need to replace the entire bottom bracket based on a loose crank arm. The threading for the bottom bracket would either be swiss or french so parts would be hard to find unless you went with the expensive Phil Wood option which wouldn't be worth it on a low end bike.

Either way, I'd find another bike shop. Look for one that does a lot of ss/fg work or a bike co-op.

time bandit

so you had to pay him just to tell you that it was broken?

wtf? i wouldnt take my business there.

mikennett

Heres a picture. I uplaoded it as an attachment so I hope that works. To be honest, I am not overly familiar with mechanics/repairs. The reason I was told that the cotter could not simply be replaced is because it is an abnormal size so any replacement cotter is slightly too big or too small - I'm currently going with too big. Either way, the crankarm retains a nice 3 inch range of zero tension making for an awkward peddling motion.

jeffmendoza

Sheldon on Cottered Cranks

mparker326

Read Sheldon Brown link other poster provided.

Take out existing cotter. Go to a LBS that has been around a while. Give them the cotter. They will put it in the cotter slots in the Park Ruler they have. They will determine what size you need. You will pay $2 for a new cotter in the correct size. May as well buy 2 while you are at it. Go home and read Sheldon Brown again on cotters & install the pin 180 degrees from the other one. Done.

The LBS you went to didn't have the correct size cotter and wanted to make more than $2 off you.

mikennett

Update: Just in cae anybody wanted to know, I sought a second opinion and it turns out y'all were right - I just needed a new cotter. New guy told me I was lucky to find the size as it was highly abnormal (called it an "R-size") and had to try about 12 before he found the right one, but now all is well. Thanks for the help - saved me a bunch and got my bike usable much quicker.