My new bike has a shimano external BB. After 4 months hard use I have noticed there is some play in the cranks. It feels like the wobble goes through the cranks (i.e. not a loose crank that would be one side only).

Is it likely that the BB is just a bit loose or is it knackered so soon? Can I get away with just tightening it? What tool do I need to do this?

Any help much appreciated

It might be knackered, it’s not unheard of, or it might just need a tad more preload on the little plastic end cap, in which case you need one of these.

The bearings are lightly preloaded, like a headset, to remove any excess play. There are full details of how to do it on the Park Tool web site. Don’t overtighten the cap or you’ll accelerate bearing wear.

If you’re going to change the bearings, which you’ll have to eventually, you may as well get a HT2 tool combining the bearing cup installation spanner and the preload thing, Park does one, but there are other, cheaper options out there too.

HTH.

BWD has given you a great answer there – said it all really. I’d just add that the Park tool is worth the extra over cheaper alternatives. It fully encircles the bearing cup giving a secure grip on stuborn or siezed bearings. Most cheaper ones only go 3/4ers round and can “spring” or flex open under high pressures.

Might also be worth checking the cups are tightly screwed into the frame.

. “It fully encircles the bearing cup giving a secure grip on stuborn or siezed bearings. Most cheaper ones only go 3/4ers round and can “spring” or flex open under high pressures.”

do you make that shit up ?

Marketeer in the making methinks.