Fitting new bottom bracket

FoldingJoe

Before I set off tonight I'm going to fit a new BB as the other one seems on it's way out.

First time fitting a new BB, so do I need to add some grease or do they come pre-greased, as it were?

Also, would it be an idea to add a touch of copper grease to the thread before installing?

Cheers,
FJ

veronese68

Should come pre-greased. Copper grease on the threads and also between the removable cup and the body if it's an ali cup. Plastic should be ok without. I had an XT BB with an ali cup seize onto the body through electrolytic corrosion or something. Took a huge lever to get it out.

greg66_tri_v2.0

FoldingJoe wrote:

Before I set off tonight I'm going to fit a new BB as the other one seems on it's way out.

First time fitting a new BB, so do I need to add some grease or do they come pre-greased, as it were?

Also, would it be an idea to add a touch of copper grease to the thread before installing?

Cheers,
FJ

The bearings, if accessible, should be pre-greased.

Definitely grease the threads, and grease the surface where the two parts contact inside the frame. Basically, use a lot of grease on anything that might touch anything else. IME BBs can creak if not well greased, and it's a royal faff to get them out just to grease them.

And go easy. Cross threading is not recommended.

FoldingJoe

I find the Shimano ones fairly straightforward.. well, compared to Campag.

tailwindhome

What's all this 'facing' business about?

mudcow007

aye, grease that sucker up, the more the merrier

in fact do it whilst naked is the only way to go

The Rookie

Erm.....what BB? BB30/External, octalink, powerspline, square etc etc etc?

TWH, if fitting an external BB the outer faces of the shell may need facing to ensure they are square otherwise the bearing may not sit square and won't last long, if the frame is pre external BB it will certainly need doing.

tailwindhome

The Beginner wrote:

Erm.....what BB? BB30/External, octalink, powerspline, square etc etc etc?

TWH, if fitting an external BB the outer faces of the shell may need facing to ensure they are square otherwise the bearing may not sit square and won't last long, if the frame is pre external BB it will certainly need doing.

Got it. What is 'facing'?

If I buy a older/secondhand aluminium frame it's likely to need done, yeah?

What about a new frame?

ETA - Thinking about taking the Cannondale Caad 5 apart and rebuilding - just to learn how to do it...

rjsterry

It's basically grinding the faces of the BB shell so that they are perpendicular to the central axis/threads. Older frames would probably need doing, newer frames designed to take external BB cups, probably not.

FoldingJoe

The Beginner wrote:

Erm.....what BB? BB30/External, octalink, powerspline, square etc etc etc?

TWH, if fitting an external BB the outer faces of the shell may need facing to ensure they are square otherwise the bearing may not sit square and won't last long, if the frame is pre external BB it will certainly need doing.

Sorry, Hollowtech II.

gtvlusso

FoldingJoe wrote:

The Beginner wrote:

Erm.....what BB? BB30/External, octalink, powerspline, square etc etc etc?

TWH, if fitting an external BB the outer faces of the shell may need facing to ensure they are square otherwise the bearing may not sit square and won't last long, if the frame is pre external BB it will certainly need doing.

Sorry, Hollowtech II.

In essence:

Copperslip
Hollowtech tool
5 mins

done.....grease the threads first with copperslip. And don't cross thread it (pretty difficult to cross thread hollowtech BB's).

mcj78

I never really understood the "facing" thing - surely if the threads in the frame are straight, there's no way that the BB could sit anything other than perpendicular to the frame - even if there was an uneven thickness of paint of a mm or so round the edges of the BB shell, wouldn't the BB just tighten against the outermost surface? Even in the case of a big blob of paint/whatever which prevented the BB sitting completely flush, would an ever so slight "high point" on the BB shell edge create enough pressure on the BB body that it affects the seating of the bearings? :?

Don't think either of the bikes I have with external BBs are faced & nothing's exploded, is the BB shell facing thing just a way to detract from the apparently poor lifespan of the external BBs? Heard plenty of folk who've had their BB shells faced & found it made absolutely no difference to BB lifespan

tgotb

This is conjecture, but what if the screw-in part of the BB isn't particularly stiff in itself, and relies on the BB shell itself to provide support. If it's screwed into a properly-faced BB shell it will be properly supported all the way round, whereas if the BB shell is wonky, it will be supported (in the worst case) at a single point. This might cause the outer race to distort under load, which would definitely impact longevity.

That said, I suspect that BB shells on most older frames (the decent ones, at least) are probably pretty square anyway, so there's probably no issue in practice

veronese68

TGOTB wrote:

This is conjecture, but what if the screw-in part of the BB isn't particularly stiff in itself, and relies on the BB shell itself to provide support. If it's screwed into a properly-faced BB shell it will be properly supported all the way round, whereas if the BB shell is wonky, it will be supported (in the worst case) at a single point. This might cause the outer race to distort under load, which would definitely impact longevity.

That said, I suspect that BB shells on most older frames (the decent ones, at least) are probably pretty square anyway, so there's probably no issue in practice

I'd say that is almost certainly the reason. Again, I don't know this as fact but that's what I thought.

mcj78

Veronese68 wrote:

TGOTB wrote:

This is conjecture, but what if the screw-in part of the BB isn't particularly stiff in itself, and relies on the BB shell itself to provide support. If it's screwed into a properly-faced BB shell it will be properly supported all the way round, whereas if the BB shell is wonky, it will be supported (in the worst case) at a single point. This might cause the outer race to distort under load, which would definitely impact longevity.

That said, I suspect that BB shells on most older frames (the decent ones, at least) are probably pretty square anyway, so there's probably no issue in practice

I'd say that is almost certainly the reason. Again, I don't know this as fact but that's what I thought.

All sounds feasible enough - I suppose it certainly wouldn't hurt to do it, however, personally i'd probably test fit the BB cups first & check to see how flush it sits before hauling the lot down the bike shop to have some paint scraped off 8)