I have a Trek Elite carbon HT. Having drifted the BB bearings out of the aluminium bb shell, do i grease the new ones prior to installation?

I would.

Yep. If it’s an Alu Shell then use what you like. No harm using carbon specific grease if that’s what you have, and possibly good if it gets trapped against carbon surfaces.

The bearings sit in an aluminium shell that is pressed/bonded into the carbon frame.

Thanks guys…i will lightly grease. Its what i though, but then i had a moments doubt…damn old age! 🙂

Yup, I use a thin smear of lithium grease when refitting BB bearings (actually, pretty much any bearings), nominally to reduce creaking, but really to make sure they’ll come out again next time 🙂

don’t mean to hijack … but will anyway 🙂

with pressed in bearings, when is grease appropriate and when should a retaining compound (threadlock type stuff) be used? Does it just depend on the application and materials?

I ask as I’ve been looking into this and opinion seems varied on the correct stuff to use

Personally, I don’t ever, ever threadlock bearings…unless I need to 🙂

What this means, is that if I get creaking cranks from a BB30 then I’ll grease it up and if that doesn’t work, it’ll get its ass threadlocked into the shell. Whatever it takes!