Retro Motobecane - help with chainring/crank

[ravenvalley]

Hi!
Converted my retro Motobecane to running Shimano Nexus 3 internal geared hub. But I will need to change the chainring, since now it's only possible to use the lowest gear. As far as I know, there aren't a lot of 3 bolt chainrings in the 25-35 teeth category. And if there are, I wouldn't know if it was easy to install it on my bike.

Which takes me to the next step - the bottom bracket. I cannot get the cottered pin loosened, but if I manage to, I suspect the threads are Swiss. Would it be possible to replace the spindle, or must I also replace the whole bottom bracket?

So, my goal is to end up with a new (single) chainring, around 25-35 teeth. And of course I dont want to spend a fortune, so what are my options?

 

[Little Al]

I would think the BB threads would be French or a small chance ISO If you can/do remove cranks & BB a spindle to suit your replacement Chain set, so long as two flanges on the spindle you intend to use are the same distance apart within 2mm or so ( lay the 2 spindles side by side ) you are good to go, there are 2 basic BB shell widths 68 & 70 mm the French favor the 68MM usually the only other thing is check your chain line.

 

[ravenvalley]

I would think the BB threads would be French or a small chance ISO If you can/do remove cranks & BB a spindle to suit your replacement Chain set, so long as two flanges on the spindle you intend to use are the same distance apart within 2mm or so ( lay the 2 spindles side by side ) you are good to go, there are 2 basic BB shell widths 68 & 70 mm the French favor the 68MM usually the only other thing is check your chain line.

Thanks, I will try that! Do I need to find a spindle with the same diameter as well, or are they all the same? Or do you mean I need to replace the whole BB?

 

[Little Al]

I would think the BB threads would be French or a small chance ISO If you can/do remove cranks & BB a spindle to suit your replacement Chain set, so long as two flanges on the spindle you intend to use are the same distance apart within 2mm or so ( lay the 2 spindles side by side ) you are good to go, there are 2 basic BB shell widths 68 & 70 mm the French favor the 68MM usually the only other thing is check your chain line.

Thanks, I will try that! Do I need to find a spindle with the same diameter as well, or are they all the same? Or do you mean I need to replace the whole BB?

Almost all the spindles are within 1/4mm the same dia when you have sorted the cranks you are going to use check your spindle to crank fit You could possibly find a low end triple MTB crank set (cotterless ) with small centre ring, you could remove the outer & granny rings & use as a single ring set if the chain line is out of line you could turn the spindle end for end the non chain side crank will be spaced out a small amount from the frame but I doubt you would notice. Any small difference in the bearing race runners will be taken up by the adjustable BB cup. It's mostly sourcing & checking the fit of various parts.