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Which is best or doesn’t it really matter?
TIA
Neither
What then? Nothing?
Check out a GMBN press fit bottom bracket video on YouTube. Technically you should use a carbon prep compound of some sort, followed by some other assembly paste. Can't quite remember, but its worth a watch.
Flame thrower
I’ve read differing views on this. Grease, carbon paste, retaining compound or nothing. I sort of get the argument put forwards about each. I’ve got a bb30a bottom bracket on my caad 13 (alloy frame rather than carbon). I just put some waterproof grease in the bb shell and pressed the bearings in. So far so good - no creaks from the bearings at all. I find from time to time when it all gets funky around the bb I occasionally get some clicking. I normally pop the xranks off, clean and regrease and put back together and then it’s blissful silence again.
Smear of Teflon grease won’t do any harm !
Metal on metal - copaslip.
Metal on plastic or plastic in metal - whatever suspension grease I'm using. Superlube, M-Prep, slick honey.
Carbon assembly paste normally has a fine "grit" in it to increase clamping force for a given bolt torque. That doesn't really apply here.
I’ve got a bb30a bottom bracket on my caad 13 (alloy frame rather than carbon).
BB30 isn't "press fit", it sits the bearings directly in the frame so actually removes the cup part. It still has issues (narrow bearings, difficult to seal) but PF has a different set. For BB30 the answer is bearing fit compound, like threadlock for non threaded parts.
The issue with press fit (imo) is there's nothing really holding the cups into the frame unlike threaded BBs so it moves arround slightly and creeks.
The only advantage of PF really was it allowed the bearing cups to be made flush with the frame which meant the chainstays/pivots could be wider (coupled with 1x drivechains).
T47 looks like a good compromise, internal bearings, with low profile cups.
In my experience, using carbon assembly paste is the worst thing to use as it is abrasive and forms a grinding paste between the BB cups and carbon frame. If it is a tight/interference fit between the cup and frame then threadlock is ok, but if there is a bit of play then a light epoxy is needed to lock it in place.
Neither. Try plumbing assembly compound. Works brilliantly.
Lard 😉
Neutral grease is the only advisable lubricant on carbon**: Park PPL-2 (or similar)
**Does it say it's specifically safe for carbon on the packaging???
Copper slip/grease is a very poor lubricant. It's a a wide temperature range anti-seize compound mainly used in the automotive/heavy industry. There are way better products for bike use. I wouldn't let it anywhere near a bike.
I use it on the outside of bearings as an extra bit of waterproofing, like the lower head set race.
Loctite 243
my understanding is press fit is designed as a compression fit to get round variable tolerances of frames (either from poor manufacture or wear/flex) so really doesn't need a grease/lube to work as designed though a small amount can help with initial insertion (oh er mrs).
Carbon prep and retaining compound.
Someone mentioned the GMBN vid. Worth a watch.
Starting at 8:35:
Nowt, never greased (a shimano) one, never had a creak from the BB on either CX, Road or MTB