Bottom Bracket Questions

benmitchell423 Posts: 29
edited November 2015 in Workshop
I have just bought a second hand frame to build up over the winter and received it yesterday. On inspection last night I noticed that it has a bottom bracket marked up sm-bb51 mountain. From a quick google this looks to be a shimano deore bb, more commonly found presumably in the mtb world.

I will be transferring over my 105-5800 kit onto the frame but will need to get a new chainset for this bike. I was going to get a 5800 chainset to match the rest of the groupset. Couple of questions,

- Would this chainset fit straight to the existing bb fitted?
- Should I just get a new bb as the cost is negligible and then I know its new and in tip top order, as I have to get a new chainset anyway?
- Is it as simple as buying a new, say 5800 bb then a chainset and removing and refitting with the new?

Sorry is the above is simpleton status but I have never been as far into the building of a bike as the bb/headset matters. I have just swapped mechs, brakes and cables before. All part of the learning process.

Any advice greatly appreciated.




  • k-dog
    k-dog Posts: 1,652
    I think MTB BBs are slightly wider so you want the one which matches your crank.

    As you say for the cost it's be worth doing anyway - much easier when you've got it all in bits.
    I'm left handed, if that matters.
  • Monty Dog
    Monty Dog Posts: 20,614
    Try it - you won't damage anything - if it snugs up tight, spins freely with no stiffness/play then it'll be OK.
    Make mine an Italian, with Campagnolo on the side..