Bottom Bracket Help!!!

Bruce0286
Bruce0286 Posts: 8
edited February 2018 in MTB workshop & tech
Morning All,

I've spent a couple of hours yesterday fitting my SLX M-7000 11 Speed RD, Sunrace 11-46 Cassette and SLX M-7000 Shifter and SRAM X1 11sp chain all is working well considering at the moment I am just using the middle 34t Chainring of my original chainset. But I know this is less than ideal and the "backpedal" issue is quite exagerated on this setup. I have a replacement bottom bracket (MT800), SLX crankset and SLX 34t chainring. My current chainset does not have removable chainrings so I need to change this.

My confusion comes in that a lot of advice online recommends facing of the BB Shell before fitting the new BB as I currently have a Square Taper BB. I contacted a highly recommended, reputable LBS and was surprised when I asked about facing they said they don't do it as it's not needed?! I even confirmed I was going square taper to hollowtech and they said nope they've done many and never faced any.

This seems at odds to what I've read online but this LBS is one that pops up countless recommendations by word of mouth and online.

If I'm doing this, I want to do it properly. What's everyone's thoughts on this?

Thanks in advance.

Comments

  • The Rookie
    The Rookie Posts: 27,812
    Its less prevalent now as most frames have an external BB in the line up so manufacturers are facing most decent frames now.

    Its not necessary that all frames need facing but it is advisable unless you are confident yours is good, an out of alignment BB won't last long, my daughters frame needed a lot of facing to get square.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Bruce0286
    Bruce0286 Posts: 8
    Thanks :).

    If I was to use something flat and place it against each side of the shell to ensure there are no visible gaps between the BB shell and the surface I use then measure several places around the BB shell with a digital caliper to ensure it is a consistent width around the shell would that be enough to be confident the shell is suitable? I already have a digital caliper, and sure I can find something flat and smooth to check against?
  • The Rookie
    The Rookie Posts: 27,812
    It would help, but the shell could be a perfect parallelogram and it wouldn't pick that up.

    When I first installed an HT2 I had some preloved bearings so just chucked them figuring if they failed quickly I'd get it faced, no issues, and that was a humble Carrera frame. ON the other hand my daughters more expensive Dirty Joe was horrendous, we had to take nearly 1mm off the highspot to get it right.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Bruce0286
    Bruce0286 Posts: 8
    Thanks, mine is a Carrera frame. But obviously that would account for little as it could be completely different. The BB only cost me about £12 so I'll just whack it in and see what happens :).

    Thanks for you help.
  • milemuncher1
    milemuncher1 Posts: 1,472
    I’ve done a few square taper to HT 2 threaded BBS, I’ve never needed to face any of them.

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