I'm just fitting one of these new-fangled internal BB's; non-drive side cup tightened up nice and easily, but fitting the drive side (with the bearing gubbins attached), the cup will not tighten right up to the frame, not amount of heaving will finish it off. It leaves about 1-2mm gap from the frame.

Does this matter? It's for a singlespeed so I am most concerned I suppose about chainline.

I tried clearing out the threads but it's made no difference.

Spacers missing?

Hmmmm. No spacers with it and I didn't think they were supposed to have any, but as you mention it the gap is exactly spacer size.

It's for an Inbred and it's a 113mm BB – anyone know if it should?

two thoughts:

1) do non drive halfway in and stop. Do drive side right up and tighten non-drive till it stops.
2) it's not a 73mm bb in a 68mm shell is it?

Good idea – I'll go and try tonight.

(Very helpful) chap who sold it to me said it had come off his Inbred, it fitted no problems on that. But great ideas, will give them a go. Thanks.

when you say 'internal' do you mean 'external' ?

An internal BB often does not screw in completely on the non drive side as there is a very slight taper in there. Fit is as basspine says.

inbreds are 68mm bb, so if its a external cup chainset it needs spacers on the driveside cup to fit,
ie, 68mm bb-1 spacer non driveside 2 spacers driveside.
73mm bb-1 spacer non driveside only

Thanks everyone. By internal I meant a square taper type BB where the bearing body sits inside the frame – sorry, not used to them, usually use HT II!

Will go for the non-drive side gap. Thansk again – I was slightly concerned about water ingress, but I suppsoe that's rather "golding the lily". Thanks again.

By internal I meant a square taper type BB where the bearing body sits inside the frame

Ah, OK, but you said "these new-fangled internal BB's" but they've been around for decades!

I was slightly concerned about water ingress

just lightly grease the threads and don't worry, water getting in there will only affect the threads

brant always suggested drillign a 5mm hole in the BB shell to let the water out.

I think you ought to be careful if the BB won't tighten properly – sounds like the threads are a bit gummed up – you won't always notice with HT2 BB's as the threaded bit is often shorter.

Sorry SFB – I meant it tongue-in-cheek but it came out a bit mis-leading!

Cheers!