shimano external BB bearing replacement

[xerxes]

Re:

I came across this some time ago: http://www.mountainbikerides.co.uk/inde ... p;Itemid=9

However, it doesn't work with all external BB cups, the RaceFace BB cups I had didn't allow you to get to the back of the bearing - you can see my comment about this on the page I linked to.

 

[02gf74]

Re: Re:

Shouldn't the bearing shells keep them parallel anyway since they are screwing into the same threads an internal would.
.

The facing removes the paint AND any metal distortions from manufacturing. The facing tool (part of the Park Tool Kit) is designed to make both sides of the shell perfectly parallel. That is the biggest killer of external BB is a non-parallel mounting. (and incorrect bearing preload).

Older frames did not need to worry about this.

 

[FluffyChicken]

Re:

I know what it does but I still don't get why it is really needed. The cups should be aligned by the threading in exactly the same way the internals are aligned. Nothing changes that. The plastic washer take out any minor imperfections or metal one would just leave gaps. That is unless you clamp them down so hard it starts to push in on the bearing seal somehow.

They are not press fitted (for HTII) like headsets, hence the threading keeps them align. If the threading is poor it wouldn't matter what style was put in.
If they where misaligned you would get the same tight/loose spots as as headset.

 

[Flynn]

Re:

Well bugger and balls, I didn't face the BB shell before I fitted the new BB but like FluffyChicken, I'm not entirely sure that it is totally necessary. The instructions that were supplied with the BB may have mentioned that as a precautionary measure but I wouldn't know because I spilled my tea all over them and then put them in the bin

With work and other commitments at the moment, I haven't actually ridden the bike at all for 3 weeks now and its going to stay that way for a while so I don't think I'll worry about it.

Interesting topic though.

 

[02gf74]

Well at least you've been shown how to replace the bearings when yours collapse after 2 miles. Fancy not having the BB faced, tut tut.

 

[Flynn]

Re:

Hahaha, beginners mistake! Must do better.

I'll let you know when the bearings pack up!

 

[FluffyChicken]

Re:

To be fair, if you don't ride it then they last longer than most.

I regreassed my bearing once (Shimano slx) and has lasted 3 or 4 years through the winters on an unfaced 24 year old bike.

Warn out the modern cheese middlburn rings first and snapped a tooth on the middle ring.

Bearing change fallowing this procedure will be next on the list. Much easier than most internal bottom brackets.