Building an older French bike into a fixed gear. Bottom bracket has been a pain in the butt. Fully overhauled it and it should be working nicely again despite some cup issues. Instead of buying a new crankset, would I be able to drill out the rivets holding on the smaller of the chainrings to make this a 1x. Would that be too sketch? If not, can I replace the BB inard (not sure the correct terminology) for a square tapered one? Any help would be wonderful, thank you!
by -damnit-
11 Comments
Drilling out rivets won’t affect the chainring structurally because a rivet adds no strength.
no way you’re going to find a replacement ring that fits really
You really should think about purchasing a new crankset (or one off Ebay). The crankset shown is all steel, & weighs **A TON**.
> If not, can I replace the BB inard (not sure the correct terminology) for a square tapered one?
You’d need both a new, square-tapered crankset, AND a new bottom bracket (also square-tapered). The bottom bracket spindle shown can only work with cottered cranks, indicated by the slotted flat spot on the spindle.
Here is some information on square-taper (i.e., cotterless) cranks
https://sheldonbrown.com/tooltips/cotterless.html
Your chainline is still going to be where it would be if you didn’t remove it; so before you go and drill this one into separate parts – I’d try running it as is. If you can get the chainline where you want it – and you really want to save the grams – then drill it out.
If you’re hell bent on using it why not just leave it as is, it’s not like it weighs a ton or would be in the way(assuming you’re going to use the large ring as your fixed gear of choice). I would be worried about how a 3 bolt crank would perform on a fixed gear too, I’ve seen a few bent chainrings lately posted in photos here. Wouldn’t it make more sense to find a BB with a more contemporary crankset option?
It’s been done. Go for it if you think you’re hard enough!
Re: square taper, we’d need the dimensions for the BB shell with the vintage cups popped out to confirm if the right adaptor exists. I’m imagining something like this [adaptor](https://www.ebay.com/itm/301825751629) so you could thread a standard square taper BB in. I’ve seen them for American BMX standards, but I’m a nitwit with vintage standards.
Velo Orange still makes a French threaded square taper bottom bracket.
I have no concerns about drilling out those rivets though
Personally, I wouldn’t drill those. Structurally, nothing to worry about but it seems like a lot of work to ruins a perfectly good vintage double crank that someone else might have legitimate use for. As other have said; just leave the inner and run it without a derailleur. Alternatively, get the French thread square taper BB from Velo Orange, a cheap (used) 110BCD crank, chainring and 1x conversion chainring bolts and have a proper setup.
One thing to note, fixie chains are wider than geared bike chains and normally have wider sprockets to match. You can technically run that chainring with a fixed chain but it might wear prematurely (probably the chain since that chainring is probably bomb proof). My first conversation was an old Peugeot with French threaded BB and I just ran the outer ring by itself with some washers to make up for the removed inner ring. It worked fine for a while.
NEVER use cottered cranks OR riveted spider interfaces for a fixed gear!
I have seen many of these fail on fixed gear conversions, either:
– the centre rivet doesn’t hold and your chainring freewheels and you loose all pedal control
– the cotter pin sheers under the load applied when trying to stop in a hurry
Either one results in a loss of control and likely a crash. Failure under pedal power is equivalent of breaking a chain – slip and smash your knee into the bars. Failure under stopping without another brake of some kind will result in no stopping and likely a similar loss of balance. If the cotter pin sheers you will now have cranks that independently rotate out their normal 180 degree sync. All of these can be seriously dangerous.
I think of how much flex I used to get out of my modern fixie with a new track frame and 105 crank set, I think I would bend them in under a hour.
The bb axle you have is Cottered and yes, you could replace it with a cotterless one , to be able to use a square taper crankset. You just need to know the length you require.