Press Fit Bottom Bracket

nellie72

I am currently trying to install a Shimano Pressfit BB (SM-BB71-41B).

My question is does the middle cartridge actually perform any function? It keeps falling out into the frame every time i try and seat it and is becoming very annoying now.

The fact that is so loose makes me think it doesn't add any value to the unit.

I am just wondering if I can fit the bearing housings without it?

whyamihere

It serves a couple of purposes. First is to keep crud away from the bearings and crank axle. Water and dirt can get in at various places in the frame. The second reason is more important. Some frames have gear cables or brake lines routed through the BB shell. The plastic cover in the middle prevents the rotating axle from getting anywhere near these and causing them to wear - This is especially important if the rear brake hose is routed through the BB area.

If you don't mind potentially having shorter bearing life and you don't have cables or hoses routed through the BB, it can be left out.

steve_sordy

That plastic tube does indeed perform an important function. It does all of the things that @whyamihere mentioned. But to do it, both ends of the tube need to be in close contact with the bearings.

Try using some grease to hold the tube in contact with one of the bearings while you fit the other. The grease should be compatible with your frame, ie choose carefully if you have a carbon frame.

nellie72

Thank you both.