…cartridge bearings inside headsets that is.

Will surrounding the cartridges with grease trap dirt or prevent water ingress?

grease stops water getting in IMO.

I tend to carefully reemove the seal (use a pin or similar) and pack as much grease in as I possibly can and then refit the seal. More grease = better waterproofing. Seals should keep grit out (should keep water out as well- but don't always). To avoid too much grit sticking, clean the outside of the cartridge as best you can.

If it's full of grease there's no room for water.

I agree with the above. No room for water! makes sense for such a slow moving application.

But over packing with grease means a sticky bearing – trying to turn over packed cartridge bearings can be quite hard compared with lightly greesed beainings in my experience?

Dunno, always had loose balls which I like to keep well greased.

lol. I'm sure you do!

IMo a smear of grease to prevent the outside corroding and never removed the seals to pack more grease in the bearings.

On this one you will get the whole range of possibilities as opinions as to the right thing to do

Do you use a grease gun for adding grease to bearings or just fingers?

i thought the OP was asking whether you put extra grease around the cartridge bearing, not in it.

I periodically re-grease the cartridge bearings in my coiler rear and apply the same theory as other posters to the headset, ie. if its full of grease theres no room for water. I also put extra grease around the headset cartridge bearings on the same theory (no room for water) and also to prevent the external faces corroding as tandemjeremy says. I wipe off any excess that gets pushed out which could attract/hold grit.

I think the Zinn book mentions something about half packing with grease which I assume is just a happy medium between no water and smooth running.

There's a good reason why the bearings aren't packed with grease.
Unfortunately I can't remember it 🙂

I prise off the seal of the baring and pack in grease. My grease gun doesn't work so I spint he bearings to work the grease around and add more in the gaps. I then replace the seals and put a layer of grease on all bits of metal that touch other bits of metal – My thinking is that this will act as a barrier (albeit temporarily) to help the seals, but also stop metal bits sticking together. I figure excess grease will work its way out of the bearing or into the tubes around it.

Howevber I try not to put too much in as it caused me a problem on a freewheel once.

No such thing as "too much grease" in a headset IMO. Freewheels are very different though.

Greasing the outside of a headset bearing will bring two benefits; waterproofing and preventing creaks from dry mating surfaces. Think carefully about the type of grease you use outside, some are more tenacious then others, I use a specific grease for in-water applications, but I've also found vasaline good for this application as well as to coat a BB body before fitting it into the sloshiest part of a bike.

if it's new, it don't need it
if it's old, it's not worth it

😉

I've started expermimenting with this.

I took a brand new (cheap) BB bearing and packed it full of grease. Before I touched it, it ran 100% smoothly. After I'd popped the seals and packed with grease it was not so smooth (say 90%).

So I'm not sure if I have a net gain or not.. It isn't as smooth, but maybe the longevity will be improved?

And I'm not sure if it was the addition of the grease which has caused the drop in smoothness, or the action of removing and reseating the seals.

depends what you mean by 'smooth' – if you mean 'free turning' then, yes, the less grease you put in the less friction/stiction there will be so it will turn more easily.

That won't last though…

There's a good reason why the bearings aren't packed with grease.
Unfortunately I can't remember it

It can cause enough pressure to pop bearing seals but I wouldn't have thought they run fast enough on a bike to do that
I pack as much as I can into headsets

The small sealed bearings used for bicyle applications are designed to run at thousands (if not tens of thousands) of RPM, at those sort of RPM's overpacking with grease would cause overheating, not really that likely in cycling applications 🙄

Kaesae would know the answer.

RIP Kaesae 🙂

Genaral rule of thumb –

If it moves (Or might seize), grease it. If it doesn't, don't. 🙂

To clarify what I mean by "smooth", I mean turning the bearing in my fingers, feeling for graunchiness/lumpyness.. I'm not referring to the effort required to turn the bearing.

What happened to kaesae then, he was some kind of bearing master so I gather?

Kaesae was THE all-knowing bearing master but he got banned for also being a complete mentalist and a tit.

He'll be reading this from bike thief heaven and wishing he could impart his bearing wisdom.

Who put those stars there? And there are only 3 letters in T1T.

I saw a kaesae youtube video about removing a pro 2 freehub using 2 pence pieces, which I did myself once. I thought it was quite a cunning trick!

Love him or loath him, Kaesae was the best thing to happen to this forum for some time.