Originally Posted by tuckervillSo if I don't want to retrofit the cranks, that means new chainrings attached to new cranks, which then means a new BB, right?
Not necessarily. I'm assuming it's a square taper spindle? There are lots of vintage and new cranksets that will fit square taper. There are also new sealed square taper BB available for cheap - no PITA adjustments necessary!
Oops. They're cottered cranks, so that makes the spindle cylindrical with a flat cut-out to accept the cotter. They look like a Lincoln Log on the end.
I'll bet that makes a difference and it would have been nice to know up front, eh?
It's either new cranks, chain rings and BB; OR new cranks to fit the old rings (with only 3 stackbolts) and new BB; OR a new set of cotter pins.
Which do you think is the easiest to accomplish?
The other measurment is the spindle length, which will determine how far out the driveside crank sits. This affects clearance of the chainrings on the stay, and chainline, which is basically how close the chain is to running in a plane between the chainrings and rear cogs. You want as little skewing as you can get to maximize drivetrain life and improve performance. Generally, 108 is for doubles, and 113 is for triples, though those numbers vary.
So that's measured from the outside of the cup to the end of the spindle? No, that can't be right. The whole length of the spindle is 142 mm as far as I can tell. I'll bet the fact that it's cottered makes a difference, huh? Yep, cuz it's 113 mm from the inside edge of one cotter space to the inside edge of the other.
But the size really doesn't matter if I'm not going to use it. I just need to know how long the new spindle should be to optimize the chainline, right?
Then, if the size of this spindle is irrelevant, with this double chainring we got here, a 108 mm BB might be best? Maybe the 113 mm, since that's how long the spindle is between cotter spaces?
Or maybe I should just try to find some cotter pins.
THANKS!
Karen