Just out of interest,
Has anyone gone back to square taper bottom brackets?
My external hollowtech bearings have seized again. Grr.
I have somewhere a deore square taper chainset that I am seriously thinking about replacing the xt hollow tech with.
My MTB doesn't get used that much. The bearings should have lasted longer than 700 miles?
I don't jet wash or ride under water.
I have a 25 year old Marin with a un55 bb that's still going strong!

Used to go through a few bearings in the early days of Hollowtech2, but generally now get a couple years out of Shimano ones and even more since have started to migrate bikes to Hope.
Assume you are not over tightening the crank when fitting and putting too much side load on the bearing? That used to be the most common cause of bearing death in the early days? As Hope say, finger tighten the preload then back off half a turn. Also worth popping the seals on Shimano and wapping in extra grease.

Oh and square taper on a couple bikes - as you say, last for ever

Currently on about 10,000km in three years on a Hope stainless steel BB, the original RaceFace BB lasted 1500km. As Wriggles says about the preload nut: finger tight then back off a touch. I'll do an annual strip down and clean and grease, but that doesn't include opening the bearing case and regreasing. If it's been a bad winter then I might do an extra service.

The performance benefit and ease of replacing on hollowtech II means I don't care if they last 1/4 of the time of a square taper!

I've still square taper on my commuter hackabout. The bike gets zero love (eg cleaned only when doing the biannual chain change) but the BB is still absolutely fine and has never even been looked at once. HT BBs on my hardtail are a different story tho, hence I currently have a stash of about 6 spares, bought when on sale.

Only problem with Square taper is when you come to remove it after 10 years its seized in the frame and a sod to remove. Killed my 1993 P7 that did

I've no figures for my HT11 throughput but we're talking thousands of miles. Several thousands.

OTOH I reckon we go through 6-10 ST BBs each year at work on a fleet of around 60 bikes. Many of those will be low mileage.

I reckon that intermittent use is the cause. Wash your bike, put it away, drag it out the shed and find that things have seized.

Has anyone gone back to square taper bottom brackets?

I did, but the new M8000 XT BBs are doing well and I do prefer HT2 as a system overall. It's the best of the external BB bunch but the older HT2 BBs were junk (less junky than FSA/Praxis etc, but still junk ). To be fair the new M8000s last a lot better than all the other past Shimano BBs - ime so far 2-3x the lifespan under the same conditions, same bikes. The sealing seems to be a lot better - it hardly existed on the older units. Quite impressed by them, using them on 2 bikes and only worn one out so far.

I reckon that intermittent use is the cause. Wash your bike, put it away, drag it out the shed and find that things have seized.

It probably highlights the basic flaw of the sealing being so poor - the dirt and water gets in then they rust or the claggy stuff solidifies.

My experience backs up Scotroutes - intermittent use is bad for HT2 BBs.

And square taper BBs are ace - it’s the crank interface that’s cack. I’ve several stripped Middleburn arms hanging in my shed to remind me.

It's the dirt/grime getting to the bearings rather than useage type that does it.

Just changed the chain on my Genesis for this weekend and found the BB completely seized (Hollowtech ii), freed it up, lets just hope it lasts the WRT

I have a Royce square taper BB coupled with a 5 arm ATB pattern (110bsd) Middleburn crankset that is approaching its 15th birthday. >30,000km ridden and fitted to its 3rd bike.
Don't make 'em like they used to anymore...

Degreased
WD40ed over night
Freed up
Regreased and refitted.
Rumbly but serviceable for the interim.

Btw think the M8000 ones are still £12.99 at CRC - bonkers cheap