I’m looking for some impartial technical advice. I’m buying a new XT chainset (external BB type), and the shop tells me I need to spend an extra £17 to have my BB shell tapped and faced.

It’s a 2002 Specialized S-Works HT frame, and it’s only ever had one cartridge BB in it in all that time. Surely then the threads and facings would be fine?

Is this retailer just trying to get a few extra quid, or is he right that tapping and facing is necessary on a regular basis to ensure life of bearings?

Any words of wisdom would be welcomed.

£17 is cheaper than a lot of places and the tool is far from cheap and the cutter needs sharpening periodically. I don’t think they are trying to bend you and when I ran HTII in an unfaced frame the bb started complaining after 2 rides.

Given you’re spending a fair wedge on a chainset a decent shop would do it for free.

For ht 11 I think its reasonable – if the faces are not parallel then the bb cups will tend to get pushed out of line when its tightened. No need for other types of BB with a cartridge that inserts into the shell but for HT11 I see the purpose

I see the purpose too, but my thought was that a frame of such quality as the “cost no object” S-Works ought to already have a BB shell that was extremely accurately engineered.

I’m just trying to cut costs – need a whole new transmission and I’m attempting to do it all off eBay or cut-price retailers, and to fit it myself if at all possible.

Don’t use HT11 then – I think its carp engineering anyway – whats wrong with your old chainset and a BB to suit if the BB has gone.

threads should be fine, facing only needed

Hmm, I’m inclined to agree – it’s not worth the risk of putting in expensive new kit if it’s not faced.

Surely it’s a 30-second job though? Anyone know where I can get it done for less than £17?!

TJ – in answer to your question, my cranks, chainrings, BB, chain and cassette are all doomed to die at about the same time, having well worn out over the past winter. So it’s time for a full upgrade and I don’t want another square-taper axle!

hollowtech mk1 aka octalink for you then

It’s more than a 30 second job that’s for sure! Also you can’t sharpen the cutting heads you need to buy new ones, £120 a pop for a Park one.

I’m still not utterly convinced facing really makes that much difference, but as said above it seems a fairly small cost to know your new chainset is fitted correctly.

why face something that is held in alignment by threads..? makes no sense to me, then add to that the fact that the cups are then tightened against nylon shims that’ll change shape when pressure is put on them..so a bit facing isn’t gonna make a bit of difference IMO.

making sure the threads are clear is important though.

when I ran HTII in an unfaced frame the bb started complaining after 2 rides.

I think that tells you all you need to know about HTII 🙁

impartial technical advice

dream on sunshine :o)

it’s not held in alignment by threads but by the ends of the shell

Very insightful SFB, bit poor by your standards though

it’s not held in alignment by threads but by the ends of the shell

yes, I wondered why the retapping might be suggested – unless the thread is damaged it’s better left alone.

then add to that the fact that the cups are then tightened against nylon shims

I didn’t know that – never having looked at one close up – but if that’s the case the whole thing is even sillier, as it will be the threads that determine alignment, and no amount of retapping is likely to change the alignment of the threads significantly without destroying them!

Tightened against nylon shims? Not always, not if you have a 73mm BB.

They definitely can be resharpened, we send ours away along with drillbits but i cant remember the name of the company that does ours.

when I ran HTII in an unfaced frame the bb started complaining after 2 rides.

when I ran 3 HTII bbs in unfaced frames they have lasted over 2 years each (both very wet an muddy summers too).

If they are installed an maintained poorly they will fail, otherwise they are fine. Facing is snake oil imho.

a frame of such quality as the “cost no object” S-Works ought to already have a BB shell that was extremely accurately engineered.

Niner are the only company (other than custom) I know of who face BB’s and disc mounts in the factory.

why face something that is held in alignment by threads..? makes no sense to me, then add to that the fact that the cups are then tightened against nylon shims that’ll change shape when pressure is put on them..so a bit facing isn’t gonna make a bit of difference IMO.

I have a first gen XT HTII and the shims are not nylon. Very tough phenolic and very accurately made. Much more so than a facing tool will manage I imagine and well within the recommended tolerances stated by the bearings too.

As has been stated you should NEVER align anything using threads, always have an aligning surface to mate to. Hence getting the opposite sides of the BB shell to be as aligned as possible.

Not prepared to get into an argument about whether this has an effect in reality but I do strongly believe that Shimano rock at engineering. They may force obsolesence on us all every couple of years, bump up prices screw us all up the a$$ annually. But in terms of good engineering practice I think they beat most of the other manufacturers. Most of the stuff they do and reccomend is for a very good reason from a structural point of view.

But in terms of good engineering practice I think they beat most of the other manufacturers.

so all those people who’ve said the bearings have seized after a wet ride have fitted them with a rock ?

my LBS charged me £10 for facing, which I thought was okay.

I’ve fitted HT2 cups to faced and unfaced frames and not experienced any real differences in bearing life (small sample I know). If it’s an expensive BB/bike then facing makes sense long term I think. For hack bikes it’s less obvious.

if facing sets the bearing alignment, this implies that the cups must be able to flex enough to take up any misalignment between the threads and the facing, so the metal at the neck must be quite thin ?

There will be some tolerance in the threads, so there will be room for misalignment.
Hence why the facing of the BB shell is important and why it controls alignment rather than the threads in the shell.

Simonf,
it’s standard practice to align a component using a faced edge. The backlash in a thread means it can happily rotate to account for a reasonable amount mis-alignment between the faced edge and the flat surface.
It’s not the cups flexing, its movement within the thread.

so all those people who’ve said the bearings have seized after a wet ride have fitted them with a rock ?

Erm… I don’t really know how my original statement implies this in the slightest. Going to ignore.

The backlash in a thread means it can happily rotate to account for a reasonable amount mis-alignment

Is this true ? So a thread can rotate to align but a bearing cannot ? The same kind of thread which subsequently seizes requiring extreme measures to undo ?

so all those people who’ve said the bearings have seized after a wet ride have fitted them with a rock ?
Erm… I don’t really know how my original statement implies this in the slightest. Going to ignore.

No, your statement implies Shimano have high standards of engineering which one might suppose would preclude rapid bearing failure…

Simonf,

No, your statement implies Shimano have high standards of engineering which one might suppose would preclude rapid bearing failure…

Which therefore suggests owners with failed BB’s have fitted them with a rock? Still don’t follow that line of reasoning.

Is this true ? So a thread can rotate to align but a bearing cannot ? The same kind of thread which subsequently seizes requiring extreme measures to undo ?

A bearing manufacturer generally states a permitted degree of misalignment. I imagine the mixed stories of failure and not will be due to a million reasons, one of which would be that some bikes will be within these tolerances from the factory floor, another bike may not. Facing the bike ensures you’re within the tolerances.

Pop a bolt on a nut, screw it up to halfway along the shaft, notice how there’s play in the nut. Tighten it up completely, this play dissapears. The nut surface is aligning itself to the top surface of the bolt.

A screwthread is a clever way of maintaining a force between two flat surfaces but shouldn’t be used to align surfaces where tolerances are important. I.e. in two pricey bearings taking a lot of load.

Again, confused as to how bolts seizing is related to the alignment issue, but seizing is usually corrosion or atomic migration. This prevents rotation of the bolt and hence makes it very difficult to reduce the mating force generated by the pitch of the screw thread.

Hope that clears it up

Pop a bolt on a nut, screw it up to halfway along the shaft, notice how there’s play in the nut. Tighten it up completely, this play dissapears

oh, I see! I had assumed that the tightening pulled it straight!

confused as to how bolts seizing is related to the alignment issue

well, I thought if there was enough room for all that play there would be enough clearance to prevent seizure…

It’s good to learn new stuff :o)

No probs :-),
To be honest most of my postulating is to justify to myself the cost of getting my frame faced all those years ago 😉