Didnt face my 456 or Meta 5, Shimano SLX BB has gone 9 months now and is still smooth !

14 months out of my xt ht2 – i think alot of the failures on stw are the trailcenter pressure washer brigade – always thought that was a shrewd business move on the trailcenters part ….

I only changed it cause i won a hope ceramic at a race im my spares box now

Also burls i agree with a good tool screws into the thread but i always thought when i was doing it at work .. Ok so thread 1 is paralel to face 1 and thread 2 is paralel to face 2 but are 1 and 2 paralel to each other ? I had a variety of face tools over a couple of shops i worked at and never came across 1 that could do all faces and threads paralel to each other …

Bottom line is for BB's they last a good 30% longer and your warranty is valid if they do burn out after 8 to 10 months rather than the 12 to 18 months they're supposed to last.

In that case, don't face it and every 8-10 months you get a new one free of charge from the manufacturer. 😯

No need.

For those saying "you might as well", I offer a frame blessing service. Only £10 so you may as well. I can do them via phone 😉

Manyt failures are due to over preloading the bearings especially on Shimano HT2 chainsets, I reckon.

oh and could someone point me to the but of Shimano's instructions that say facing is necessary?

trail_rat – Good point, I suppose it depends on how they are cut in the factory. Would like to think it's done after the frames been welded as welding can damage the threads and in the larger companies sure to be done by machine. If it's clamped and a twin headed cutter is used won't be a problem but if the frame is flipped because it only has one cutting head could create a slight error. The geek in me would like to have a look at how bike frames are made in the bike factorys.

I asked Brant exactly that in the previous version of this question. Pretty sure he said they are cut separately.

To summarise:

It has been statistically proven that 75% of BBs fail due to over preloading the bearings especially on Shimano HT2 chainsets. The remaining 75% fail because of pressure washers but only the coin operated ones at at trail centres. Kaesae is at least 30% correct in stating that you will get 50% longer bearing life from a faced frame. 9 months is an acceptable BB lifetime.

It's good to see that we can have a pragmatic discussion and personalities are not influencing the advice.

I knackered a new BB in one race – granted it was the Muc Off 8! I faced the frame and now have one BB still going strong after 6 months whereas I was wearing them out approx 3 months at a time.

And no – no jet washing, no mistreatment (other than racing) and I only weigh 75kgs.

Clubber, will you bless my frame please? I'd feel much better… 😀

Some questions for those who follow the BB facing folklore…

If you screw an external BB bearing in to the BB shell until it just contacts the shell at one point, what is the clearance between the BB bearing and shell at the widest point ?

What is the maximum reduction in thickness of a BB spacer under the compression of normal tightening of the BB bearings ?

If the answer to the first question is less than the answer to the second question, why get the frame faced ?

What is the maximum misalignment allowed for the bearings used in BBs ?

What is the maximum misalignment found on unfaced frames ?

If the answer to the third question is less than the answer to the fourth question, why get the frame faced ?

If cycle manufacturers put a 12 month warranty on their bikes, then why don't they face all BB shells to avoid the inevitable warranty claims for failed BBs?

Oh come on Graham you can't just come on here and be logical about it!

Not enough grease packed in the bearings, Over-tightening & cleaning the bike with either a pressure washer or Muc-Off type stuff is what kills HTII type bearings.

And that folks is a "Bike Fact" 😉

Sticking my engineering hat on (ok, electronics, but engaging brain at any rate) – a few possible reasons I can think of that might require them to be faced (assumes the threads each side are correctly on-axis, which you'd kinda hope there are):

if there's a large misalignment, the external bb cup's only going to contact at one point – I don't think it should wind itself out 'cos of the thread direction (not to mention the cranks holding it in), but as a result the thing might wander in the threads (I think someone on the forum's had a knackered frame from something like this)

if there's small misalignment, the bearing shell might seat ok 'cos of a little slop in the threads, but the bearings would be running a little off-line and possibly bind a little, or not spread the load so effectively.

Same thing should apply with headsets.

Certainly wouldn't have been much of an issue in the days of loose/caged ball bearings (rather than cartidge bearings) 'cos you had to sort out the tension/feel by hand. Might be why CK insist in facing headtubes – assuming their bearings are closer toleranced (I've no idea if there are, mind) then it's more critical, the slacker the tolerances in the bearing then the more it'll tolerate a slop frame fit (but equally may not spread the load across the bearings as well, so would wear faster I'd expect).

Any mechanical/bearing engineers in the house with an informed opinion ?

>If cycle manufacturers put a 12 month warranty on their bikes, then why don't they face all BB shells to avoid the inevitable warranty claims for failed BBs?

I'd guess added cost of manufacture vs the cost of a possible warranty claim – of all bikes bought I'd guess a lot don't get ridden enough in the first year for any failures to show up, and of the rest I suspect many just replace the BB and don't think about claiming under the warranty

(fwiw, the older 'dales I have/had certainly had the bb's faced – not sure 'bout the headtube – and my '03 sworks enduro had bb, headtube, disc mounts all faced)

jond – Member
Any mechanical/bearing engineers in the house with an informed opinion ?

Yep, but only about 25 years in industry dealing with sealed bearings from 10mm to over 1000mm in diameter, many in quarrying applications which kill pretty much everything.
But I don't want to spoil the opinions of a few who have whacked some into a bike a few times 😉

" takisawa2 – Member

I've never bothered. If I was buying a nice, shiny, expensive new frame then probably would, but not on the piles of tat I usually hack around. "

Always strikes me that if it's a nice, shiny expensive new frame then it ****ing well shouldn't need faced.

There is only one symptom that indicates the need
for facing the bottom-bracket shell. When attempting to
adjust a high-quality adjustable-cup bottom bracket with
new parts, the spindle feels smooth through a portion of
its rotation and tight in another portion of its rotation.

When tapping a bottom-bracket shell it is a simple matter to go a step
further and face the bottom bracket as well. This is
cheap insurance to enable easy adjustment of the bottom
bracket and maximize the longevity of bottombracket
parts. For this reason, some shops will routinely
tap and face bottom-bracket shells on high-end
bikes.
In the case that a shop sells bare framesets, it is a
good marketing technique to face them before putting
them out for display. Knowledgeable customers will look
for whether facing has been done to evaluate whether
the frame has been properly prepped for assembly.

Barnetts Manual of Bicycle Repair

When attempting to adjust a high-quality adjustable-cup bottom bracket with new parts, the spindle feels smooth through a portion of its rotation and tight in another portion of its rotation.

Why would misaligned bearings cause that ?

Knowledgeable customers…

What knowledge would that be then ?

Always strikes me that if it's a nice, shiny expensive new frame then it ****ing well shouldn't need faced.

Bingo.

Knowledge of mtb folklore…

Frames need facing if you're fitting a chainset that requires a crank to bottom out on a splined interface at a given distance across the axle to achieve the correct preload on the bearing, and you don't have access to cup or axle spacers of different widths to achieve the correct fitment.
e.g. If you have a 73mm shell and wish to fit a Raceface or Truvativ chainset with a 2mm driveside cup spacer, it's a good idea to assemble the chainset before fitting it into the BB to measure the distance from the preload washers across the axle, then measure the distance across the BB cups through the centre where the axle would sit.
Typical measurements across BB's are 98 – 101mm, and typical axle measurements are 96 – 100mm depending on the chainset and BB used of course.
The goal is to get the BB measurement to no more than 1mm wider than the axle spacing width to achieve the best possible fit allowing for compression in the preload washers and BB bearing cup axle sleeves to eliminate side loading of the bearings while still getting a snug fit.
I have 5 years of data to back this up based on maintenance records of demo and Hire bikes used at a trail centre.

1mm and 0.5mm spacers are now commonly found in X type BB fitting kits, but until recently it was necessary to face BB shells to accomodate some chainsets.
And that's where I think the whole facing debate originated.

So to summarise, it is necessary in some cases, but not all if you get your spacing right, or fit Shimano cranks.

MrOvershoot – Member

,,,,,,,,,,,,,,,,
Not enough grease packed in the bearings, Over-tightening & cleaning the bike with either a pressure washer or Muc-Off type stuff is what kills HTII type bearings.

And that folks is a "Bike Fact"

Mine on a genesis IOID ( raceface) was full of grit after strahthpuffer – maybe 300 – 400 miles on the bike in total. Never washed with a power washer or with muc off and nothing done to it since original seemembly

To me there are two issues
1) crap sealing and vulnerable to dirt entry
2) potential for misalignment – hence the need for facing. Tehre is a clearance in threads and if the outer faces are not parallel when the cups are would in they will end up slightly off parallel as well.

I think its a crop system all in all. I have other bikes with octalink and its much better