Weird bottom bracket

[derge]

While stripping a donor bike I came across this nice YST threaded BB. Does anyone know anything about it? I’ve been unable to find anything about this particular model. The bike was supposedly from 1997.

The plastic, accordion-like bit in the middle is odd, I can’t figure out why it’s there. Just a cheap easy way to fill the space I guess?

 

[Fastpedaller]

Those 'dust tubes' just intended to stop crud falling down the set tube into the bearings - quite a common part in the 80's. I think I still have one in a garage drawer.

 

[fossyant]

My old Dura Ace threaded BB has the plastic 'tube' to keep any crud out - e.g. water getting down seat tubes.

 

[derge]

That makes a lot of sense - it was grimy!