Thumpic

I found this in the bb...is it just to hold the bearings during assembly???

thanks..........

cuevélo

I think that it's to keep water out the bearings and tubes, or to keep rust out of the bearings. All the mid to high quality cup and cone bottom brackets that I have taken apart have had one.
A mountain bike that had rusted a lot on the inside had a pile of rust on that plastic piece and it kept that rust from getting in the grease of the bearings.

rhenning

Many older better bottom brackets had that part. It goes over the spindle between the bearings and races. Keeps the water from washing out the bearing grease. Roger

Thumpic

in this instance...it didn't work........but thanks for the responses......................

DMF 

Is there a hole in the hanger tube to drain it?

pgoat

they rarely worked, but better than not having one....when overhauling a BB I used to slather grease all inside (after cleaning out the old grease residue)

Bikewer

Hehe- I once found a dead wasp in the BB shell....

masiman

These were not perfect seals but they did help a great deal for bottom brackets that had cutouts.