How important is it to face the BB Shell?

spongtastic

How important is it to face the bottom bracket shell when installing an external BB crank?

I have an 04 Malt One frame, a FSA headset set of LX cranks.

My not so LBS want £40 to install, and obviously I don't want to pay that much, which on top of an hours drive counts up to quite a bit.

The heasdset isn't a problem as I can use a mates press, but there seems to be disagreement about the crank, some say just do it, others say no way.

Any opions?

clas

very

if you dont the bearings will be loaded unnaturally and fail sooner. it may also cack up your drivetrain

The Big Cheese

As above - essential with Hollowtech II and X-Type external BBs

omegas

Lots of different opinions on this subject, some people fit hollowtech and never have a problem with misalignment some people have constant squeaking cranks.

A lot of talk about facing the frame when the most important part to get done is the threads chased as this give the true alignment across the hollow shaft.
I have not seen how the bottom bracket thread is cut into the frame and at what part of the manufacturing stage this is done. If the thread is cut at the later stage it will be done with a double alignment mandrill so that the threads are cut parallel to one another, if not the standard type bottom bracket would not align to screw the locking collar on.

So how accurate does this have to be done? Probably with in .003” if not when the thread is chased as recommended my Shimano it would cut them out of the frame. So don’t be drawn to much into the facing of the frame as this can be of a tolerance again something over .003 What is important is the alignment of the two threads as if this is out you will load the bearings in a horizontal and vertical plane.

All bearings are manufactured with a clearance built in for expansion from heat, which is not a problem for a bottom bracket.

So the choice is yours, do I just fit them myself and see how long they last or pay someone to chase the threads and face the frame.

nicklouse

In Shimanos fitting instructions they say the bb shell must be faced.

And omegas facing has nothing to do with the thread alignment.

the thread could be perfectly aligned but the faces could be miles out.

omegas

Hi nicklouse

My previous post is just saying make your own mind up take your own chance, I am sure everyone that works in engineering has there own opinion on this subject.

The design of the hollowtech bottom bracket mounting system is used widely in industry on all types of machinery for mounting bearings. (two bearing cups screwed into a housing or shaft.

A 25mm shaft running at 1000 rpm with 0.08mm run out in the horizontal and 0.03mm in the vertical is an acceptable standard worked to in engineering, in simple terms the closer tolerance worked to is the thread to thread alignment the secondary face to face. This standard defines acceptable limits for shaft-to-shaft alignment of coupled machines. The limits are defined in terms of maximum offset and angularity.
These are perpendicularity, parallelism, straightness, roundness, flatness, eccentricity, and run out.

If the face to face has run out when the shaft is perfectly aligned the load is transferred into the threaded cup or bearing housing causing premature failure of components.
Its all about what is a acceptable amount of face to face misalignment for a set of cranks turning at approx 90rpm.

I am sure I written a paper on this about 30 years ago………..

supersonic

Quite often you see damaged and galled faces on bb shells, usually due to the chain getting jammed between the shell and crank.

dennisn

Rotor SABB makes a bottom bracket with bearings that swivel in the housing
thereby allowing everything to line up. Fits Shimano and some others. Kind
of expensive though. Of course.

Dennis Noward

artillerydave

I would say visually inspect your bottom braket faces to see how they look before fitting, if there is a massive overspray of paint or it feels / looks rough then I would get it faced, personally, I am on my Third Merlin frame an 04 malt, an 06 Malt and a rock lobster B52 and all were visually fine, not faced and the BB (LX hollowtech 2) is still sweet as a nut and smooth as anything. If the frame is poorly prepared (Merlin seem not to be) then get it faced. Also Omegas soulds like the kind of person who knows what he is talking about (didn't understand a word of it)

nicklouse

To sum up if you understand Omegas and have the background and knowledge do what you want.

Other wise get it faced.

And a smoothly rotating shaft has no similarity to a crankset axle.

It is amazing how many creaky X-type/HT11 cranksets have not had the bb faced. Also the ones that keep on finding that their cranks come lose Oh guess what they did not have the bb faces checked and faced if needed.

TBH i do not care. I charge more to do it if i have to strip it all down first. and then there is the explaining that the housing has warped Also you will find that top end bike mechanics do chase and face everything before doing a custom build.

struck

thats a stupid question dude always get it faced if it isn't already. if the frames second hand take it to shop to check its been done properly

clanton

Ok - so how faced is faced? I took my Cotic frame to have the bb shell faced to a bike shop that has a good reputation locally (NOT my LBS!) and they faced the frame (I watched them do it) but there was still lots of paint on it - should it have been all shiny metal or is that not needed?

struck

either side needs to be flat and perfectly parallel. some paint isnt a problem but i prefer to get it to the metal without cocking up BB dimensions

stevebrock

i just had my BB shells faced on my 07 Rockhopper, reason being that i'm installing a Hollowtech Xt Crankset and the factory one was an internal octalink BB.

My LBS charged me £15 to remove the octalink BB and face the frame!