I'm having an issue with a cotter pin bottom bracket. There was a loose at first so I dismantled the whole thing down. I fixed the bearing issue but now I noticed that the left crank arm is loose on the BB axle. I'm just not sure how to fix this. Any ideas?

Did you get the flat on the correct spot on the spindle?
Is the cotter seated fully?
Did you swap cotters from side to side? Supposedly, upon initial installation, the flat is filed to fit.

I've put the right cotter to the right side and the left cotter is flat to flat. Seems like the flat spindle part is larger than the cotter. Seems like the crank moves in and out and back and forth.

Did you whack the fat end of the cotter pin to set it, or just use the other end's nut to draw it tight? Cotters need a solid strike to get tight. Andy.

+1, cotters need to be pressed or hammered in with much greater force than can ever be achieved by tightening the nut. You're lucky because most people who try to draw the pin via the nut end up stripping it. Once the pin is driven home, the nut keeps it there.

If it was tight before and you did not change the BB spindle or cotter pin then you did not tighten sufficiently. Cotters are quite soft metal - so that they can more easily conform to the spindle flat. As FB noted that means they must be pressed or hammered home, but if using a hammer it's important to note that you need to support the crank arm so that you have a firm base and do not damage the bottom bracket bearing. The other issue is that due to the softness if you ride for any significant distance with a loose cotter you can damage it so that it does not mate properly, and the cranks will loosen even if the cotter is tightened well.

The cotter got hammered into place. I recall that there was a play there when I first got the bike. I can try hammer it more to see what will happen. Also the cotter looks different than the other side. It's flatter where the other one as a indent.

Did it look like this?



If so, the pin is damaged and must be replaced; no amount of pressing or hammering will eliminate the slop.

If one side has an indent and the other has play even when hammered you need to replace both cotters (should always do so anyway). there is one common diameter, but also two others, so take the cotter in with you or measure it in mm with calipers. It's possible you will have to carefully file the flats. Plenty of guidance available by searching for cottered crank. As usual Sheldon offers some of the best info.

John,
you might have answered my question. The right side (good one) pin looks like your picture but the bad one is kinda flat. I will replace it and see what it does. Thanks for your help.

Always replace cotter pins in pairs unless you know they came from the same source. The cut angle of the wedge varies brand to brand, so mismatched cotters will have the cranks not line up 180° apart.

If you need a new pin, but two.

Thanks FBinNY. That's a great tip/

Can the bottom bracket be upgraded to those square taper ones by changing both the crank and BB?

I think it could but I want to preserve the cranks as they have Raleigh imprinted.

Yes. If that's what you want.