BB not lasting long

[kwwmackenzie]

Hi, After about 5 months my first bottom bracket packed in, it was a shimano one (cant remember the model). I replaced it with a wheels manufacturing BB which lasted about a year. I then had a bike shop replace that one in about march. It honestly lasted about 3 weeks. So I replaced it with a Shimano 7900 Dura-Ace towards the end of April and now its about to go (the usual noise from a bb thats on its last legt). I can get rid of the noise temporarily with cleaning and some grease but it will come back within a few miles. My question is, is there anything that would cause the BB to pack in so quickly (at the moment I'm reluctant to spend much on one if I dont know its going to last). I have a cube hooper pro hybrid and do about 60 miles a week commuting.
Any thoughts would be appreciated.
thanks

[DaveM]

That is very quick for a BB to wear out. Are the bearings in them actually getting loose/failing? Or are you replacing them because they are making noise? If its noise, the BB itself may be fine. The noise could be coming from the BB moving around in the frame, from the crank arms, from the pedals, or even something else on the bike.

I assume these are all cartidge BBs. When you say "cleaning and some grease", where are you cleaning and adding grease?

As a general note, be aware that buying "top of the line" stuff like Dura-ace doesn't mean your getting the most durable part. At that level you're paying a lot extra to reduce weight/friction and the parts may actually be less tough than a decent mid-range part. But again, I'm suspicious that the problem isn't really the BB itself.