Changing to triple -Octalink or Hollowtech II ?

[Mr Pig]

If they are screwed in right I don't see how they will move beyond the tolerance in the thread.

The thread doesn't define the absolute position of the end cap.

Think of it as a bolt. Say you screw a bolt onto a threaded hole in a block of steel. Now imagine that the face of the block is not square, not at ninety degrees to the hole, but is slightly off. The bolt will zip into the hole until the head of the bolt contacts the top of the block. Obviously the head of the bolt will not be flush onto the block, it will be touching on one side but not the other. What happens next depends on the strength and configuration of the two parts.

As you tighten the bolt further what will typically happen is that the shank of the bolt will bend as the threads pull on the head, allowing the head of the bolt to sit flush on the surface. Obviously this will weaken the bolt and if the shank bends enough, is put under enough stress, it might fail immediately.

This is what I can see happening in a Hollowtech bearing. The bearings are effectively mounted in the head of the bolt so could end up pulled off of true to the threads/frame. As I say, I've not used a Hollowtech bearing but I've seen this often enough in other, similar assemblies to know it happens.

 

[Steve Austin]

So, would you recommend folk get their frame faced then Mr Pig?

The theory goes that if you don't your bearings will only last a short period of time. No one can specify what this 'short' period of time is though.
I really can't see how a smear of paint on a BB shell can affect the angles of the bearings, and I genuinely believe if your frame needs facing then its a manufacturers defect and the manufacturer should have to foot the bill anyway. I love fettling with my bikes, but that doesn't mean I want to buy a bike that needs 'finishing'.

 

[Mr Pig]

So, would you recommend folk get their frame faced then Mr Pig?

Like I say, I've not fitted these myself, of even looked at the parts in the flesh, so I can only guess. But I doubt I'd bother. I'd fit the bearings and look at how the mated with the frame. If it looked good I'd tighten it up progressively and feel how the bearings were running. If they ran smoothly, job done.

If the faces were off you could tighten until you felt the bearings start to stick, then back the thing off slightly. You might get away with something like that.

If the bearing housing distorted significantly the bearings would not last very long at all! ;0)

 

[Smokin Joe]

I would say that the cups are too large a diameter to distort as they mate on the face of the shell. None of the (albiet few) people I know who fitted outboard bearings bothered to get the frame face, none had problems and all of the frames were pre-outboard days when manufacturers would have had no reason to face the shells.

 

[mickle]

I never did establish why the industry abandoned the perfectly good square taper. I've got a RaceFace Turbine crank on a RaceFace Ti BB. Five years old and still going strong, as light as anything and I'm a clydesdale.

On the bearing discussion I'm with the Pig.

 

[Mr Pig]

I never did establish why the industry abandoned the perfectly good square taper.

My guess is that they need something to do!

Manufacturers have designers working for them who need to justify their salaries, they need to go into work and do something. They need to change designs for the sake of it, otherwise they're out of a job.

And everyone is happy with that. Manufacturers want to be seen to be moving forward, pushing the technology, and I'm sure that often we get genuine improvements. Sometimes though things will be changed just to make them look more technical, or to make manufacture or assembly cheaper.

I would say that the cups are too large a diameter to distort

They might well be, I've not seen them. Or rather it might be very hard to distort them. I certainly think that it should be possible to fit them without facing the frame if care is taken. Like I say, I'm just guessing, but I can see why manufactures might feel that facing the hole is prudent.

The other factor we've not talked about yet is loading. These bearing housings effectively sit on the outside of the BB and the load from pedalling will be transferred to the outer edge of the hole in the frame. If the bearing housing isn't supported all the way around it may distort under load.

 

[Steve Austin]

Outboard bearings and the matching crankset are stiffer. thats why. Noticeably stiffer.

Got them on all my bikes now

 

[Dave5N]

Well all I can say is that in my rather limited experience (sample of 1 bike, though stamped on in 'cross) it has so far worked fine unfaced.

Quite prepared to take a different view if/when it fails because the faces aren't flat and parallel.

 

[xpc316e]

Why bother with all this new-fangled stuff? Just buy some new old-stock square taper stuff from fleabay and forget about facing the frame and the headache of working with unfamiliar systems. I managed to recently buy some new old-stock biopace stuff on ebay, and I am chuffed with my purchase.

 

[Mr Pig]

Outboard bearings and the matching crankset are stiffer.

Which makes sense. The further out the bearings are the less the crank shaft can rock on them.

 

[PpPete]

Why bother with all this new-fangled stuff? Just buy some new old-stock square taper stuff from fleabay and forget about facing the frame and the headache of working with unfamiliar systems. I managed to recently buy some new old-stock biopace stuff on ebay, and I am chuffed with my purchase.

Believe me, if I could find a suitable 9 speed triple chainset for square taper - on ebay or elsewhere - I would be on it like a shot. I've read all the arguments for increased stiffness from bigger diameter and so on, and I'd still be quite happy with square taper. Getting the BB is no prob - even MTB cranksets can be found, but decent quality triple road cranksets (52/42/30 or similar) with square taper seem to be unobtainable now. Unless you can point me in right direction?

 

[Steve Austin]

I'm pretty sure you can find Campag cranksets in that size shape readily available. check Bike+ and GB cycles

 

[PpPete]

Good thinking Steve... but all 10 speed, and all too expensive for me (even when they are half of RRP !)

 

[02GF74]

BB facing hmmmmmm, don't like the sound of that. I wasn't aware of this and have fitted one such set to a friend's; will need to check up on it but it seems to be fine.

I wonder by how much out of parallel the opposite BB faces need to be to cause a problem?

You would have thought a BB was a tube faced off at both ends so should be pretty accurate to start off with, well, perhaps not on a £ 99 argos bike.

 

[PpPete]

A number of previous posters seem to have gotten away without BB facing.

My own feeling was that if the outboard bearing units are torqued-up as recomended by Shimano (around 50 Nm as I recall) - and the spindle goes through with no trouble, then the axes in the bearing units must be

A) parallel
in line with each other

which implies that the shell threads were true with each other and the faces were parallel or, if the faces were not parallel, then the recommended installation torque is insufficient to distort the bearing housing..... in either case facing would be un-necessary.

However if you put the bearings in and the spindle didnt go through - then not only should you have faced the shell, but also re-tapped the threads to ensure it all lines up.

I was prepared to chance it - as my bike is not of the £99 Argos variety - but in the end I an Octalink unit came up on fleabay before a Hollowtech II one so the choice was made for me.