Facing your bottom bracket, or not?

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  • Facing your bottom bracket, or not?
  • endurokid
    Member

    So,

    I got my new frame home and realised that my LBS didn’t face the BB for me, even though they should’ve done, there didn’t seem to be any bubbling or lumpy spots around the BB with regards to the paint so I just fitted the BB and left it, its been on for a month or so with no problems but I wanted peoples opinions on this?

    I can’t see it causing any problems but you never know!

    Cheers

    Premier Icon Northwind
    Subscriber

    I never have. Some came faced, another was done when I had the frame in for other work, didn’t make any difference that I can tell. I did chase some thick paint off one of my Mmmbops though but just to flat it back to the metal, no actual “facing”.

    Premier Icon mrblobby
    Subscriber

    Past few frames I’ve had didn’t need it. Funnily the last one I did it to was an mmmBop, but that was just for a bit of paint too. I’ve read that the HT2 style bottom bracket is fairly tolerant to small misalignments between the faces, and other BB’s have different levels of tolerance. May be b*llocks though as I think I read that on here!

    Premier Icon faustus
    Subscriber

    Some magazines suggested this was a ‘must do’ but it’s crap. Never done it, and still on original BB after 4 years and 2 different frames. I check the face for lumpy paint, and would lightly sand any if needed.

    endurokid
    Member

    I’m running a Hope BB, not sure what difference that will make. It doesn’t really both me as the paint seemeed pretty straight around the BB, it was just one of those questions that I meant to ask to see if anybody had had any issues!

    Cheers

    johnners
    Member

    Don’t the BB shell threads (rather than the faces) take care of the alignment?

    toys19
    Member

    This ^^^^

    I am convinced facing is a myth, if you search under my user name you will see I have done countless analyses of the issue in various ways and have yet to find any evidence that it is anything more than a ruse invented by park tools to sell expensive gear and help LBS’s to sell the procedure.

    Premier Icon midlifecrashes
    Subscriber

    Your BB is going in to your frame in whatever alignment the threads are cut. Scraping a bit of paint and/or metal off the outside edge of the shell is not going to change that.

    Premier Icon cp
    Subscriber

    Don’t the BB shell threads (rather than the faces) take care of the alignment?

    Not at all no, there is plenty of play in a thread so once the bb shell butts up against the frame, any misalignment of that end face relative to the face on the other side will cause the BB cup to be distorted.

    I’ve not done it to the last few frames with no ill effects – most alu. BB shells are machined off anyway, so should be no need. Paint is easy to remove if there’s over-spray.

    Premier Icon mrblobby
    Subscriber

    Don’t the BB shell threads (rather than the faces) take care of the alignment?

    May be b*llocks though as I think I read that on here!

    Would seem reasonable!

    Not at all no, there is plenty of play in a thread so once the bb shell butts up against the frame, any misalignment of that end face relative to the face on the other side will cause the BB cup to be distorted.

    As does this!

    toys19
    Member

    Not at all no, there is plenty of play in a thread so once the bb shell butts up against the frame, any misalignment of that end face relative to the face on the other side will cause the BB cup to be distorted.

    I have measured every single one of my frames with a shimano cup and a dti and have yet to find any measurable play.
    If you look at the park tool the clearance between the cutter and the shaft it spinds on means that the cutter will just align to any face misalignment anyway.

    endurokid
    Member

    All interesting reading, cheers guys!

    clubber
    Member

    It can be an issue but IME it’s so rare that it’s a non-issue.

    I’m still convinced that the myth comes from an early batch of external BBs that failed quickly but warranty was rejected due to not having had the frame faced – eg an excuse to avoid paying out.

    endurokid
    Member

    I’m still convinced that the myth comes from an early batch of external BBs that failed quickly but warranty was rejected due to not having had the frame faced – eg an excuse to avoid paying out.

    Makes sense.

    johnners
    Member

    Not at all no, there is plenty of play in a thread so once the bb shell butts up against the frame, any misalignment of that end face relative to the face on the other side will cause the BB cup to be distorted

    The BB shell is part of the frame, and it’s quite a fine thread so “plenty of play” is a bit contentious. I also don’t see a cast BB cup deforming that easily.

    I don’t think I’m buying the whole facing fetish.

    I’m still convinced that the myth comes from an early batch of external BBs that failed quickly but warranty was rejected due to not having had the frame faced – eg an excuse to avoid paying out.

    …but that has the cynical ring I’m looking for in an argument!

    ndthornton
    Member

    I faced my bottom bracket last week.
    Iv been putting it off for ages as he has a bit of a mouth on him.
    I plucked up the courage and told him straight…. I said “I’m sick of this! You cost the best part of £50 yet for some reason you cant cope with a bit of muddy water. I mean this is England for Gods sake.. what did you expect! The first sign of bad weather and you start crunching, creaking, dragging your heals and complaining like child… Well Iv had enough, this is the absolute last time I’m changing your bearings. If this happens one more time its the bin for you I promise!… I’ll go back to my old square taper… Don’t you laugh at me! He may have been a bit floppy and his cranks did fall of occasionally but at least he didn’t faint at the sight of a puddle!”

    We haven’t spoken since

    toys19
    Member

    I also don’t see a cast BB cup deforming that easily.

    Johhners see my calcs on this from a while back, it moves by a very very small amount, much less then the angular float of the bearing.

    fasthaggis
    Member

    I am convinced facing is a myth

    Yup ,I think the same ,never done it or felt the need.

    toys19
    Member

    ok this is for press fit headsets, but the theory is broadly similar.

    http://singletrackworld.com/forum/topic/are-superstar-headsets-any-good#post-5104402

    endurokid
    Member

    Well, the general consensus is I’ll be fine, which is the answer I was looking for!

    clubber
    Member

    It’s worth noting that Shimano don’t nor have ever said anything in their fitting instructions about facing.

    Given that external BBs came along at a time when no one had ever heard of facing BB shells (ok slight exaggeration but accurate to all intents/purposes), if it really was an issue they’d have been keen to mention it to avoid loads of bad press about how poor external BB life was.

    They never have because it’s not a real world issue.

    johnners
    Member

    Johhners see my calcs on this from a while back, it moves by a very very small amount, much less then the angular float of the bearing.

    Calcs you say? Right, that settles it! I’m going to continue not facing any BB shells, just like I’ve been not facing them for the past 10+ years.

    Premier Icon mrblobby
    Subscriber

    So what about facing head tubes then? 🙂

    Edit: Ah I see toys19 has that covered!

    clubber
    Member

    Well I would say that head tubes are faced or at least should be square as part of the manufacturing of the frame, same as BB shells. If it’s not, most people would rightly complain that the frame wasn’t properly finished.

    The issue was the transition from internal to external BBs and the use of that as an excuse to avoid some warranty claims.

    what about deformation during the frame build?

    the bb especially, you have 4 tubes joining the bb shell with an awful lot of weld?

    Premier Icon Onzadog
    Subscriber

    I think this came about because so many of the early bottom brackets died in double quick time. People were looking for an explanation (someone to blame) and they picked on shell facing.

    Personally, I think the nylon washer is compressible enough to take up a bit of misalignment. Any more than that and it’s a thread issue that facing isn’t really going to help.

    A lot of early demise on HTII type bottom brackets is due to people over tightening the preload cap. Oddly enough, the same thing happened with headsets when things first moved over to A-headsets.

    The deep groove ball bearings in bottom brackets don’t like lots (or any) side loading.

    In short, fit the bottom bracket properly and don’t worry about facing.

    Premier Icon Nobeerinthefridge
    Subscriber

    Threads keep the BB aligned, a headtube is a far better candidate for facing.

    Premier Icon MSP
    Subscriber

    As I always write on facing BB threads.

    With a shimano style crank, ie slide the arm onto the spindle and tighten the pinch bolts, it doesn’t matter because the crank design allows for some adjustment.

    However with a crank that uses a bolt to draw the cranks together, ie race face, then the width of the BB shell is important, there is no room for adjustment in the crank design, so the BB shell needs to be at the specified width. If it is wider even by a single mm, then the bearings are either overstressed or the cranks aren’t fastened properly. Which is why raceface have such a bad reputation for bearing life, and the cranks working loose.

    Premier Icon scotroutes
    Subscriber

    MonkeySpacePilot wrote:

    As I always write on facing BB threads.
    With a shimano style crank, ie slide the arm onto the spindle and tighten the pinch bolts, it doesn’t matter because the crank design allows for some adjustment.
    However with a crank that uses a bolt to draw the cranks together, ie race face, then the width of the BB shell is important, there is no room for adjustment in the crank design, so the BB shell needs to be at the specified width. If it is wider even by a single mm, then the bearings are either overstressed or the cranks aren’t fastened properly. Which is why raceface have such a bad reputation for bearing life, and the cranks working loose.provide shims to adjust for any tolerance issues.

    The RaceFace BB on my fatbike has just died. That’s almost exactly 24 months of regular (ab)use. RaceFace sell bearing replacement kits too.

    Premier Icon MSP
    Subscriber

    They didn’t use to provide shims, guess they have realised the design flaw.

    Premier Icon scotroutes
    Subscriber

    Dunno. This is the first/only RF BB I’ve owned!

    shandcycles
    Member

    Threads keep the BB aligned

    No they don’t. Not if the cups are tightened up against the shell. It’s not really debatable, it’s just a simple engineering fact. There needs to be clearances in the mating threads to allow the threads to work, so the cups will always align to the face of the shell, not the thread. Assuming of course that the shell is close enough to being perpendicular to the thread bore that the cups don;t bottom out on the threads before the cups bottom out on the shell. That kind of setup isn’t unique to bicycles either.

    However, most decent frames will have the shell close enough to being square that facing probably isn’t needed.

    toys19
    Member

    shandcycles, with the greatest respect, that is utter bollocks.

    shandcycles
    Member

    shandcycles, with the greatest respect, that is utter bollocks.

    ahh, the wisdom, care to elaborate?

    toys19
    Member

    😀 read my previous posts that I linked to.

    shandcycles
    Member

    read my previous posts that I linked to.

    that looks like interesting stuff. I’ve read the post about the headset cups in an unfaced headtube. Do you have similar analysis for a threaded cup and misalignment?

    shandcycles
    Member

    toys19 – just as an aside, one thing I picked up on in your previous post was this :

    What would make the cups not parallel? The cups have 10-20mm of parallel stub going into a tube (also parallel) can you explain how facing influences how the cups go in?

    I’m not sure how much influence it’s going to have on your calcs but the bore on each end of a headtube is not (often) going to be parallel or concentric. The heat (assuming a welded frame) is going to distort the headtube so it’s no longer straight but is bowed. And that’s why you both face AND ream the headtube so that your getting closer to a parallel bore on each end. The same is true with a BB shell. Because on both a headtube and a BB shell most of the joints are on one side only of the tube, the tube (again I’m assuming a welded frame) will always bow to some extent no matter the skill of the joiner.

    toys19
    Member

    I don think this tool will improve the parallel-ness or concentricity of anything.

    shandcycles
    Member

    I think using a cone as first pass on one end and a relatively deep insert on the second pass on the other end will get things close enough for what we’re talking about needing done.

    I feel I’m going slightly off-topic here a little as really I was commenting on the fact that if the faces of your bb shell aren’t perpendicular with the thread bore then when tightened, a bottom bracket that seats on the face of the shell, *may* have issues with binding and premature wear.

    I’ve seen this many times when a bb is swapped out for a different type. I admire the analysis you’ve done but it doesn’t alter the fact that I’ve fixed binding bottom bracket spindles by chacing and facing the shell and I bet many other mechanics have too.

    toys19
    Member

    I’ve seen this many times when a bb is swapped out for a different type. I admire the analysis you’ve done but it doesn’t alter the fact that I’ve fixed binding bottom bracket spindles by chacing and facing the shell and I bet many other mechanics have too.

    I would need to see this in the flesh, the bottom bracket and headset tools are so flawed I cannot believe they would make any difference, and I am utterly unconvinced that any bottom bracket shell face misalignment has any bearing on the bearing..

    The threads on a BB are fine pitch, and large enough diameter that they totally control the alignment of the BB. I measured lots of bb shells using a shimano cup screwed in to leave a 1mm gap, the BB cup, using a dti to 0.01mm did not register any movement on firm hand pressure. In fact I got more movement out of a seat tube by squishing it with my hand pressure.

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