Replacing caged headset bearings with sealed

I think you will need to use conventional caged bearings or loose balls, unless you want to change the headset.

If the bike is high quality, but old, the headset might be "sealed' even though the bearings are just in a cage. The seals will be in the headset body instead. 

Mountainbikers sometimes "bodge" additional external seals by stretching a piece of old innertube arround the outside of the headset (usually lower bearing as that's the wettest place). Needs to be done as you reassemble the bike.

I would just put in lots of good quality water proof grease and leave it that.

Stop reading here, boring bearing chat incoming.

A bearing in any machine (including a bicycle) usually has a few basic parts:

-rolling elements (e.g.,balls): hard, precisely made, expected to wear out within the lifetime of the machine.

-races: surfaces for the rolling elements to run on. Hard, precisely made, expected to wear out.

- a cage: holds the rolling elements apart. really only useful in high speed applications, where you don't want fast spinning balls touching each other where they move in opposite directions. Also makes assembly easier. Cheap materials, not precisely made, expected to wear out.

-seals: to keep lube in and dust/water out without creating too much friction. Expected to wear out.

-a housing - holds bearing race in the right place.  Lower cost material. Not so precisely made, not expected to wear out.

Different types of headset arrange these parts in different ways:

- Traditional: races and housing are "one" (sometimes the race is a harder part permenantly fixed inside the housing). Can have seals on the housing.

- Modern external: headset is the housing, standard industrial-type bearing units containing rolling elements, races and seals are dropped in, May be extra external seals on the housing too. Since the wearing parts are in one place, they are quick and easy to replace, and the part with the cool US brand name on it should last forever.

- Modern internal/hidden: The bike frame is the housing, standard industrial-type bearings dropped in. Nowhere for a logo, so bad business for makers of high end headsets.

Other bike parts (hubs, BBs etc.) have followed roughly the same evolutionary path.

Headsets are a weird application for bearings, since they hardly go anywhwere. That makes them prone to odd sorts of failure, because the rolling elements are always sitting in basically the same spot, with shock loads from bumps bashing away at the races. This can lead to "self centering" behaviour, and regular dents visible around the race when you take it apart and inspect. 

There is a reasonable argument, when replacing caged bearings in a traditional headset, to ditch the cage and just use loose balls. Upside: more balls fit in, so loads spread over more material. Downside: fiddly to do, risk of balls going everywhere when you eventually take it apart.

Thank you. I feel better now.

I've only ever seen sealed bearings with flat and angled surfaces as the ball or roller bearings are enclosed inside (hence 'sealed') so it's unlikely you'd find any that fit directly in the curved space in the bearing cups. That doesn't mean someone doesn't make them but I can't see much demand. 

I think a complete headset change is the only way to go for sealed bearings. I swapped a 1" steerer threaded headset to a threadless aheadset once but this was because I was replacing the forks so it was worth the effort.

Both my Chris King and XT headsets havesealed units, but they contain bearings that seem to be the same 5/32 bearings that were in my headset bearing cages when I had them, so the units would be bigger than the cage bearings.

At least that's my quick take on this, I quite happily stand to be corrected.

Not something I've ever attempted, although I'd investigate whether it's actually possible before sizing up new bearings, buying a new tool, etc.