Bicycle Mechanics - Plastic BB cups - OK or junk?

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DinoShepherd
04-07-05, 01:10 PM
UN-73 BB. The square taper Shimano style. I have noticed these have come with both aluminum and plastic BB cups.

Questions:

1) Which came first?
2) Is one considered an upgrade or a cost saving move?
3) Do the plastic ones tend to squeek less?
4) Is the plastic as robust (durable) as the aluminum?

The reason I ask is that I recieved one of these today with the plastic cups. First I have seen...

<edit: I do mean the removable cup is plastic. The other is still aluminum.>

Any feedback is greatly appreciated.

-Z

Rev.Chuck
04-07-05, 01:16 PM
About the only time you can mess one up is if you tighten it with the tool crooked. I think they creak less.
fsor
04-07-05, 01:43 PM
VERY TIMELY!
I just got one of these as well and freaked. Does the plastic cup take the same torque as the AL? I did not get any installation info. Thanks!

pmseattle
04-07-05, 05:46 PM
I don't like them because the plastic seems cheap and shoddy. Having said that, I have an old mountain bike with lots of very hard miles on it, and it still has the original ( 1996 ) BB UN-53, which still turns smoothly with no end play, and has never emitted creaking noises.
Rowan
04-07-05, 09:11 PM
To my mind, they are better than the alloy ones. Less likely to sieze in place. You do need to be careful threading them in as the threads can be destroyed relatively easily. As far as I am aware, they don't have a stressed function, other than stabilising the body of the cartridge so it doesn't flex up and down on that side.
mtbikerinpa
04-07-05, 09:22 PM
The plastic cups are designed to be a cheap wieght loss as well as an anti-creak device. Since it is completely encased in the bottom bracket shell, there is no issue with cracking in use. I have never seen a case of the plastic cup cracking or deforming, but in a freeride bike I would still feel more secure with a metal one.