never really known the true answer to this so any knowledge appreciated, ive had mine in about a year, so should it be on its way out? (xt one)

remove cranks – turn the bearings and feel if they’re ‘gritty’. How bad you let them get is down to you but I tend to replace mine before they get more than just ‘a bit’ bad as I’ve foudn they start squeaking.

remove chain from chainset, spin chainset and listen for any noise / see how freely it spins. this will give you indication of BB condition, ie if it only spins around once I`d suggest BB bearings on way out, similarly if spins but is noisy

re: jamesb suggestion – I’ve always found external BB cranks barely spin when new so I’d be careful about assuming the BB is shot just from the spin test.

yes point taken (eg Campag Record doesn`t spin too freely at first), just a bit of a simpler test than having to remove crank arms.
Also can test for side play by gently rocking side / side crank arms, gives indication of bearing wear

The above advice is OK for the perfectionists…however it’s perfectly possible and OK to run your bearings beyond the point at which they are rough, as long as you are careful that you are not damaging something non-consumable.

One of my bikes has a UN52 with a bit of play and I’m still riding it OMG!

It either has a lot of play in it (when you grip the cranks and move fom side to side) or it is stiff to turn.

Nothing else matters, except creaking. But rule #1 of creaking is that it’s never the component you think which is making the noise.

Disassemble, degrease and check bearing tolerances carefully, if they exceed manufacturer’s specification then replace. Or… notice the cranks are moving up and down as well as round and round, which is generally a bad sign.

‘Dead’ things are generally pretty obvious aren’t they? And the latest spec HT2 bearings, which I presume are what you have, last an awful lot longer than the old ones, so just because they’re a year old, doesn’t mean they’re fecked. You can always very carefully pop off the plastic top-hat things, use a pin to remove the bearing seal, clean with WD40 and re-grease if they feel gritty but have no play.

But if they go round, don’t make weird noises or display obvious symptoms of wear, like play, I’d just leave them to it and go riding 😉

#1 Pedalling is hard because the axle is rotating in the bearing. Water got in and the inners have corroded and seized.
#2 They knock when you push and pull sideways on the cranks indicates that they are worn inside. They can continue like this until it affects your shifting due to the chainrings wobbling about
#3 They feel gritty when turned by hand – on their way. Consider lifting the seals and flushing them with GT, then re-packing with grease. Or just leave.

Well just replaced mine as it was very noticably wobbly, had thought the pedals were the cause, took a look noitced a wobble through the crankset, rode it one last time and it was quite noticable wobbly. Unless it’s seized up just keep going, what the worst that can happen?

Though removing the cranks the inspecting the bearing, maybe re-greasing them (careful removing the tophot) wouldn’t hurt…
http://www.mountainbikerides.co.uk/index.php?option=com_content&view=article&catid=24:drivechain&id=35:shimano-hollowtech-ii-bottom-bracket-bearing-replacement&Itemid=9