Originally Posted by
juvela
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The OEM chainset is not cottered but rather Thun pattern. This arrangement does not employ the shell's threads. What appears to be a cotter on left side crank arm is actually a pinch bolt. Loosen the nut and arm will slide off the spindle's splines. You can then unthread left side bearings and right hand arm with chainwheels will come right out. Spindle is permanently affixed to rh crank arm.
Since the shell's threads were not employed by the chainset you may discover that they need to be chased/cleaned to get BSC dimension fittings to thread in.
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I tried this and it seems jammed or something. The chainguard is also badly warped so I'm thinking there might be some damage to this part of the bike. If like another poster mentioned there are no bb threads, will a threadless bottom bracket work?.