My Fatbike has a 100 mm BB shell, with a Race Face external BB (Team XC IIRC). The left bearing is getting a little rough after 3 years. A replacement is $47.

I can buy a Shimano XT for less than $20, but its for a 73 mm shell. So I’d need to use the longer plastic tube from the old 100 mm BB that fits between the BB halves.

Will the RaceFace tube work with a Shimano BB? ❓

I’m not interested in a Hope, King, or other ‘spensive one! 😡

the plastic tube isn’t needed. Depending on the frame it might help keep crap out of the bearings.
Probably just give it a go

^ Yes, I know that its not needed structurally.

But the Fatty is my nastier weather ride, so keeping the crap out of the bearings is important on this bike.

The only crap it’s keeping out is the stuff coming in from holes in the frame though, how much silt had built up in the BB area when you changed it?
If it doesn’t fit in the shimano one a length of poly pile the right diameter would probably do the same thing.
If you’ve got 3 years out of a RF one then I reckon your probably fine.

I swapped my fat bikes FSA for an XT last month just as you described

Chucked the middle bit away, and had to use the spacers provided. Everything is happy now, and running sweetly

I used the race face tube with a deore BB in my fatty, works fine

ditch the tube and drill a small drain-hole in the BB shell

(probably voiding any warranty but I’d still do it)

Rocketdog – that’s what I was hoping to hear. Thanks. 🙂

Yes you can swap them, I’ve used road bb’s on my mtb and visa versa and just swapped the tubes.