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Hmm ok Yes, its a weird component on a bb
Majority of bbs I have serviced have the plastic ring instead of metal and it travels right to the bearing. The cheaper bbs have them but its not the best seal, you still end up with grit etc.
I suppose the plastic ones are used for a tighter seal to "try" keep the weather out and the metal ones could be used for the crank arm installation.
It wouldn't be ideal for a plastic ring to be pressed against a machined edge with a crank arm tightened on. The ring would fail or your crank arm would get loose.I have not seen one before that stops at the machined section but I know for sure, that little ring does not keep the spindle in place. The bearings contacting the spindle inside the shell keep it in place.
but yes weird haha
gubhi-
I know for sure, that little ring does not keep the spindle in place.
Yeah, never meant that, meant as a stop for the cranks. I've seen plenty of shitty seals come off like you mentioned and it's not one of those, the picture way back didn't look like one either.
Could also be to stop the chain getting stuck but the one I had up there is a 113mm and I don't think there would be room for that anyway.
snottyotter
Had one in front of me. Pried it off a bit and you can see it butts up against the machined section on the spindle, it's made of steel and too far away from the bearings to be of any use as a seal or dust cover. They're there to stop you installing the crank too far on, you may not need it if you reach installation torque before they contact but if you don't it'll stop them going on too far. Most BBs don't have them and I've always thought they're a bit weird.