New bottom bracket

[raleighnut]

Always use Copaslip on a square taper BB, after all you might want to get the crank off again at some point. ( Copaslip- Anti seize assembly compound)

 

[mrandmrspoves]

Strangely enough, greasing the taper ensures a more secure fit and less chance of it working loose. The mechanism by which this happens is counter-intuitive. I like to explain it like this. Imagine a scrubbing brush with bristles of say 20mm. Place the brush on a carpeted surface, apply a little bit of pressure (just enough to bend the bristles) and now move it sideways say 10mm. You'll notice that the bristles bend to the side but don't slide on the carpet due to the friction between the bristles and carpet. Now pull up on the brush and at some point you'll notice the bristles catch up with the brush body and move over.
The same happens inside the crank's square taper. As the crank bolt forces the aluminium crank up over the taper, there is resistance between the crank and spindle to slide. No matter how tight you make the crank bolt, you can see that as soon as you somehow enlarge the square hole a little bit, the crank will move over without additional force from the bolt being applied. This actually happens when you pedal. The trailing face on the square taper relaxes and the crank moves up onto the taper, not down. This leaves the bolt loose and it can unscrew. The bolt cap prevents it from falling out but if you work on enough square taper cranks you would have come across a bolt that's completely loose inside.
If you grease the taper, the crank moves easier onto the taper and does less settling under pedaling forces. That's why it is better to grease than not to grease the taper. However, there is always a little bit of grease residue on the taper in anyway, since it is lightly greased at the factory to protect it from rust, so greasing more is only necessary if you suspect that the taper was supplied absolutely clean.
The last time I even saw a cottered crank was in my childhood. Thank goodness that madness has disappeared. Octalink has other problems and is definitely not a better design than square taper. It was borne out of necessity, but not as an improvement.

This one could be almost as hotly debated as helmets. I have heard both arguments, for and against. I have never had a problem not greasing - so stick with that approach. I have seen loose crank bolts on a few occasions - canot recall if they were on greased or ungreased crank. I must say I do not miss cotter pins!

 

[Stantheman]

The new BB felt great today, lovely and smooth. Well worth the effort and little expense. I will check the crank bolts every now and then for tightness.

 

[Blue Hills]

The new one I fitted today had some white stuff which I assume is some sort of thread lock already applied on the non drive side.

The white stuff could be anti-seize. Shimano's anti sieze is a sort of white gloop

I grease everything - BB threads plus cranks.

Helps things mate I think and also come apart more easily.

 

[chewa]

I grease the cups (it stops any creaking for one thing), but previously I had never greased a taper in my life. (Is that a euphemism)?

I do make sure that I use a torque wrench when doing up the cranks though and have only in the last year had issues getting an arm off (the crank has been on for maybe 4 years). It took days of soaking in plusgas to get it off so for the replacement I used some copperslip and torqued up as usual. Best part of 800 miles later all still ticketyboo.