[Closed] Facing your bottom bracket, or not?

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".

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!

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.

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

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

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.

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.

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.

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!

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.

All interesting reading, cheers guys!

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.

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.

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 [i]is[/i] 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!

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

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.

I am convinced facing is a myth

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

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

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

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.

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.

So what about facing head tubes then? 🙂

Edit: Ah I see toys19 has that covered!

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?

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.

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

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.

[quote=MSP ]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 [s]have such a bad reputation for bearing life, and the cranks working loose.[/s]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.

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

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

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.

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

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

ahh, the wisdom, care to elaborate?

😀 read my previous posts that I linked to.

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?

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.

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

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.

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.

Well, I don't know what to say. What I do know though, is that if I screw a cup into a shell and the face isn't perpendicular so I have a gap on one side and not the other. Then I keep tightening 'til that gap goes away, then something has either moved or deformed. Whether that has an impact on the smooth running or longevity of the BB I guess depends on the BB or where/how it's moved/deformed. But I know it happens.

Just for balance, and to illustrate I have no axe to grind, I very rarely face the shell ends on bikes we build.

I face bb shells as a matter of course when bullding bikes.
It's amazing to see that mid way through facing a frame, you can sometimes see paint and material removed from one part of the face but not the other.
I also chase threads through to make sure they are aligned with one another.
For me it's simply correct practice to make sure that the bb is starting life off in the best circumstances possible.

To the OP - just fit a square taper crank and UN55 bb and forget about alignment 🙂

Slightly off topic so apologies to the OP (talking head tubes not bb shells).

toys19's headset analysis is very nice but unfortunately does not describe the actual mechanism of most headtube misalignment. It shows a misaligned tube where the end faces are not perpendicular to the bore. Pretty much all mass produced quality frames start with a head tube that has been faced / bored in a lathe prior to assembly (so begins life perpendicular and parallel).

Welding or brazing the frame concentrates a lot of heat on the rear face of the head tube, and if you get the heat wrong it pulls into a visible banana shape. So the end faces and bore are still locally perpendicular, but the top and bottom faces are no longer parallel (more than 1mm out if you really go crazy with the torch).

Similarly, if the head tube has short overhangs above top tube / below down tube (so ends are near the heat), then it can also flare / ovalise.

Provided these misalignments aren't too big, then they can be corrected by facing, without which it can be impossible to fit cups / headset will have tight spots. Sometimes the headset problems are actually caused by the out of round / localised excessive interference causing deformation of the (realitevly thin) bearing race.

toys19 also suggests that it needs 1400 kg to close the misalignment gap on his headset analysis model. This is probably correct - and the thread on a relatively stout headset press can generate forces far in excess of that figure. In the day job I've run bolt torque vs clamp load tests on M24 fine pitch bolts and generated forces well in excess of 100 kN (actually a lot more force than that but haven't got the data at home to quote). So briefly back on topic - maybe a fully tightened bb thread generates a lot more axial force than you think.

Similarly, any animal fitting a headset by the hammer and wood block method can attest that it is very easy to fit a cup out of parallel with the bore, and it is only when it comes up against the faces that it squares up.

mick_r cheers for the response there are a couple of points I would like to raise.

it is very easy to fit a cup out of parallel with the bore, and it is only when it comes up against the faces that it squares up.

I am not sure I agree with this, and have never seen it. In my experience you can start it off out of parallel, but very soon, long before the cups touch the face, the thing straightens out. If it does start out of parallel you tend to get marks on the cup parallel faces too. There are many pics that will attest to the fact that even after pressing your headset in there can be a gap on one side due to a non square face that no amount of torquing with the press will resolve (because they tend to have parallel press tool faces so they cannot force the cup out of parallel) . (can I find a pic like this now? When I need it? No, but I have seen them, honest)

I agree about the possibility of weld distortion, but I will admit I have never seen it, if I bought a frame with this I would send it back.
But to try and remedy it with any of the market available hand tools is a ridiculous notion, there is so much backlash in the contact between the reamer/facer and the shaft that it rotates on that it will just conform to whichever direction it decides to take, plus how do you set your datum? The cone it uses at the other end will never ensure centralisation. To do this you need a lath, mill or boring equipment. Any aftermarket facer/reamer just makes it look pretty.

Facing BBs - my feeling is that it's more about removing paint bulges and the like. The BB shell does distort fractionally when welded or brazed (though very little if made properly), the issue is more a powder or paint drip causing a bearing shell to distort slightly.

Head tubes are a different issue - the cups are thinner and more easily deformed, and there's no thread to control the insertion and alignment.

The hand tools might not get it absolutely perfect, but they get it close enough to solve the problem.

My LBS told me that if I didn't face my BB I'd die of cat aids 😳

Personally as yes I am quite the homo, I prefer the rear mounted bracket. Gives me more support in the general anus area.

Peace
#mountainbikesaregay

[quote=The Flying Ox ]Personally as yes I am quite the homo, I prefer the rear mounted bracket. Gives me more support in the general anus area.
Peace
#mountainbikesaregay
😕