Spun the cranks on my old bike and it did sound quite loud and uneven so resolved to replace bottom bracket. Finally removed today and its a square taper shimano un 73 – the xt of its day! It looks in pretty good condition since its been in there for just over 7 years. Not ridden much in the last 2 years so that makes 5 years of almost continual use. Now debating whether to risk it and fit to new frame or to get hold of the supposedly much inferior un54 – any thoughts??

i ran loads of 73's and 54's and couldn't really tell the difference. think the 54's have a plastic sleeve, but you can use the metal one from the 73 I think.

there's no obvious external signs of wear on these (unless the taper is shot), but rough feeling and odd noises generally indicate getting shot. I used to run mine till there was obvious play (grab hold of crank and see if there's and wobble – if there is, make sure it's not chainrings or something like that before replacing bb!)