External BB bearings - worn?

For discussions about bikes and equipment.
User avatar
Sweep
Posts: 8444
Joined: 20 Oct 2011, 4:57pm
Location: London

External BB bearings - worn?

Post by Sweep »

I know this will make me seem like a total beginner (I'm not) but I only have one bike with external BB bearings - the Shimano set-up.

And as I don't live with the thing I haven't ridden this bike many miles at all.

So - to the point.

With my various cartridge BBs (square taper/Octalink) I have always checked for wear by grasping the two cranks and trying to wobble them apart by pulling them both towards and away from the frame. Any wobble/movement it means that the BB is worn out and I replace the cartridge. Of course with square taper in particular this doesn't happen very often.

I have just tried the same thing with the Shimano external BB and am getting slight movement.

Does this mean that the bearings are worn out and need to be replaced?

Or could something else be afoot?

Another question - will also look particularly nooby, but I don't have a full set of tools with this bike and so can't easily at the moment take things apart to have a look - fair to assume that even though this bike was fitted with external bearings from the beginning by Hewitt that a full set of threads are in the BB shell so that I can i time replace the questionable external bearing jobbie with a square taper? (I have standing by a good quality Deore square taper crankset which I think is a very near relation of the Deore external BB in there at the moment.
Last edited by Sweep on 16 Nov 2021, 8:33am, edited 1 time in total.
Sweep
freeflow
Posts: 1637
Joined: 29 Aug 2011, 1:54pm

Re: External BB bearings - worn?

Post by freeflow »

A small amount of movement along the axis of the crankshaft is normalish, though you might want to loosen the bolts on the left hand crank and check the bearing preload after the right hand crank is pushed fully home.
User avatar
cycleruk
Posts: 6065
Joined: 17 Jan 2009, 9:30pm
Location: Lancashire

Re: External BB bearings - worn?

Post by cycleruk »

3 tools needed to service/change external BBs.
https://www.chainreactioncycles.com/shi ... p-prod3784
https://www.chainreactioncycles.com/shi ... p-prod3785
(other makes of tool available) and an Allen Key.
Be aware there are 2 sizes of cups and you may need an adapter if the smaller type is on your bike. :x

If the movement is rocking then could be worn but possibly a bearing cup is loose and needs tightening.
Also check that the left crank hasn't come loose ?
You'll never know if you don't try it.
User avatar
Sweep
Posts: 8444
Joined: 20 Oct 2011, 4:57pm
Location: London

Re: External BB bearings - worn?

Post by Sweep »

freeflow wrote: 23 Oct 2021, 1:54pm A small amount of movement along the axis of the crankshaft is normalish, though you might want to loosen the bolts on the left hand crank and check the bearing preload after the right hand crank is pushed fully home.
many thanks freeflow - it's only slight so I can I think relax for a while.

Part of the reason I checked is that I had a "soft crash" recently - ended up in a bit of a heap on a grass verge after failing to take a bend in the wet :(

After checking and finding this slight/very slight wobble I just tightened up the crank bolts - which kinda leads to another question - do folks use a torque wrench for this? A torque force is clearly marked on the bearings.

On the other question, I assume that - if I wanted to - I could just replace the whole caboodle with a square taper? Once I had figured out what spindle length I needed.
Sweep
User avatar
Sweep
Posts: 8444
Joined: 20 Oct 2011, 4:57pm
Location: London

Re: External BB bearings - worn?

Post by Sweep »

cycleruk wrote: 23 Oct 2021, 2:22pm
Be aware there are 2 sizes of cups and you may need an adapter if the smaller type is on your bike. :x
Thanks for the reply cycleruk
Is this related to whether it's an MTB or roadie type set-up?
If so this will be the MTB one.

I do have a tool like the one you linked to (mine is Park) - I think it's the right size but since the cranks haven't been off yet haven't been able to check.

See my question above about the torque wrench.
Sweep
slowster
Moderator
Posts: 4629
Joined: 7 Jul 2017, 10:37am

Re: External BB bearings - worn?

Post by slowster »

Park Tool video here - https://www.parktool.com/blog/repair-he ... on-slotted

Although it is over-tghtening of the bearing pre-load cap on the left hand crank that particularly needs to be avoided (and is demonstrated in the video), I would not want any loose play either, since it is easy in my limited experience to get the pre-load just right, i.e. the point at which side-to-side play in the cranks disappears.

The fact that the play appears to have been cause by the impact of a soft crash would make me suspect that something had been pushed or compressed out of alignment. In your shoes I would want to loosen and remove the LH crank, slide the RH crank slightly out and then push it back into position, and then follow the re-assembly procedure in the Park Tool video.

In my experience the bearing pre-load torque is so low that a special tool is unnecessary. I just use the corner of a plastic squeegee like the one in the link below. In other words almost any piece of flat plastic with a right angled corner should fit between opposing splines in the cap and allow more than enough torque to be applied.

https://www.amazon.co.uk/3M-Hand-Applic ... 00657SFPE/

With regard to fitting a square taper bottom bracket, the bottom bracket shell usually has to be faced when an external BB is fitted, i.e. to ensure the bearings are parallel. If a square taper cartridge is then fitted of the type with no flange or flanges which are not very wide, e.g. UN55, then the bare metal of the bottom bracket is likely to be exposed. It might not look pretty, but I would try to put some Hammerite or similar on the bare metal. Square taper cartridges with flanges/lockrings which completely cover the sides of the BB shell are much less common.
User avatar
cycleruk
Posts: 6065
Joined: 17 Jan 2009, 9:30pm
Location: Lancashire

Re: External BB bearings - worn?

Post by cycleruk »

My External BBs are on road bikes but I didn't see any difference when I fitted an MTB external to one of my bikes. They all work on the same engineering style.
I'm not sure which BB had the smaller diameter cups but it did need an adapter to fit :-
https://www.chainreactioncycles.com/shi ... prod137442

I have never used a torque wrench but having 60 years of engineering experience I generally have a feel for what's right or not. :roll: :oops: :shock: :)
You'll never know if you don't try it.
User avatar
Sweep
Posts: 8444
Joined: 20 Oct 2011, 4:57pm
Location: London

Re: External BB bearings - worn?

Post by Sweep »

Thanks for all that slowster.

will bear all in mind.

Anyone any views on the torque wrench thing?

I have all the other necessary tools to hand I think but this is so far what has discouraged me taking things apart - I don't have a torque wrench with the bike at the moment.

I don't know to be honest if this slight looseness was caused by the off - somewhat miraculously there was no visual sign of any damage to the bike, me or my clothes - this I put down partly to my well stocked panniers :) - it is very likely that no appreciable force was applied to the cranks at all.

Thanks for the good point about the facing - will look at that issue closely if I do switch to square taper - would be interested in any reports from folk who have made this switch.

I am aware of the facing issue - in fact I know someone who had to take a Hewitt back once maybe twice because it appeared that some facing issue was causing repeated bearing failure.

Another question (sorry!) related to this - it is my impression that if you ride an internal cartridge bearing when the bearings are past their best you won't do any real harm - just maybe have some slightly frustrating rides. If you ride with external bearings that are somewhat shot, can this cause future issues with the facing at all - ie interface between bearing and frame?
Sweep
User avatar
Sweep
Posts: 8444
Joined: 20 Oct 2011, 4:57pm
Location: London

Re: External BB bearings - worn?

Post by Sweep »

cycleruk wrote: 23 Oct 2021, 3:56pm

I have never used a torque wrench but having 60 years of engineering experience I generally have a feel for what's right or not. :roll: :oops: :shock: :)
I have no engineering background whatsoever and can be somewhat ham-fisted :)
Sweep
nsew
Posts: 1006
Joined: 14 Dec 2017, 12:38pm

Re: External BB bearings - worn?

Post by nsew »

Sweep wrote: 23 Oct 2021, 3:09pm
Part of the reason I checked is that I had a "soft crash" recently - ended up in a bit of a heap on a grass verge after failing to take a bend in the wet :(
The front brake is set up for that sort of thing to happen. Turn the adjuster at the lever out (CW) a few turns - loosen off the cable and re-tighten with the pads against the rim - turn the adjuster back in (ACW) until the wheel spins freely. The objective is to get the vertical edge of the cantilever arms parallel to each other for maximum braking performance (MA).
Attachments
8D67F5D1-4DBF-44F9-A820-83EB98E47FED.jpeg
User avatar
Paulatic
Posts: 7804
Joined: 2 Feb 2014, 1:03pm
Location: 24 Hours from Lands End

Re: External BB bearings - worn?

Post by Paulatic »

Sweep wrote: 23 Oct 2021, 4:09pm
cycleruk wrote: 23 Oct 2021, 3:56pm

I have never used a torque wrench but having 60 years of engineering experience I generally have a feel for what's right or not. :roll: :oops: :shock: :)
I have no engineering background whatsoever and can be somewhat ham-fisted :)
There are pages of torque wrench debate on this forum. Along with Cycleruk I’ve never used one on a bike.
Perhaps if you’ve a history of things coming loose or over tightening and stripping threads then a torque wrench might be a good investment.
Whatever I am, wherever I am, this is me. This is my life

https://stcleve.wordpress.com/category/lejog/
E2E info
peetee
Posts: 4292
Joined: 4 May 2010, 10:20pm
Location: Upon a lumpy, scarred granite massif.

Re: External BB bearings - worn?

Post by peetee »

Your first step is to remove the crankset and inspect the axle. I have come across several instances of worn through-axle cranksets caused by seized bottom bracket bearings. It is, I consider, a flaw in the design of the external BB system that the axle is a press-fit through the bearings because when the bearings seize the axle can still rotate, often with little apparent additional friction, leading to the crank axle mating surfaces wearing away and the owner having to replace an expensive crankset as well as the BB.
Highlighted here:
viewtopic.php?f=5&t=112675&p=1103732&hi ... n#p1103732
The older I get the more I’m inclined to act my shoe size, not my age.
User avatar
Sweep
Posts: 8444
Joined: 20 Oct 2011, 4:57pm
Location: London

Re: External BB bearings - worn?

Post by Sweep »

nsew wrote: 23 Oct 2021, 4:49pm
Sweep wrote: 23 Oct 2021, 3:09pm
Part of the reason I checked is that I had a "soft crash" recently - ended up in a bit of a heap on a grass verge after failing to take a bend in the wet :(
The front brake is set up for that sort of thing to happen. Turn the adjuster at the lever out (CW) a few turns - loosen off the cable and re-tighten with the pads against the rim - turn the adjuster back in (ACW) until the wheel spins freely. The objective is to get the vertical edge of the cantilever arms parallel to each other for maximum braking performance (MA).
cripes that is a bit of detective work - appears to be the bike in question.
The brakes are essentially as set-up by Hewitt (as I said I haven't done tons of miles on it) though obviously the pads have worn with my riding.
Will check things out - thanks.
Must say I prefer V brakes.
If I'd been more switched-on when buying the bike I would have specced V brakes and a square taper crankset - I still feel these possibilities should have been put before me as an option.

as for the crash - a bit complicated - a very bad downhill bend in the wet.
Sweep
User avatar
Sweep
Posts: 8444
Joined: 20 Oct 2011, 4:57pm
Location: London

Re: External BB bearings - worn?

Post by Sweep »

peetee wrote: 24 Oct 2021, 8:08am Your first step is to remove the crankset and inspect the axle. I have come across several instances of worn through-axle cranksets caused by seized bottom bracket bearings. It is, I consider, a flaw in the design of the external BB system that the axle is a press-fit through the bearings because when the bearings seize the axle can still rotate, often with little apparent additional friction, leading to the crank axle mating surfaces wearing away and the owner having to replace an expensive crankset as well as the BB.
Highlighted here:
viewtopic.php?f=5&t=112675&p=1103732&hi ... n#p1103732
thanks - will check out - I should stress that the bearings still appear to spin just fine - it's just the slight side to side movement (when given pretty hefty force) of the cranks that I had noted.
Sweep
slowster
Moderator
Posts: 4629
Joined: 7 Jul 2017, 10:37am

Re: External BB bearings - worn?

Post by slowster »

By side to side play, I take it you mean that you can hold the left hand crank where it fits on the axle and push and pull the axle back and forth in the bearings*? How much play is there - 1mm, 2mm, more?

* As opposed to play in the bearings themselves, which is only/most noticeable when holding the crank at the other end by the pedal, i.e. angular movement magnified by the length of the crank.

With regard to a torque wrench, I can understand the reluctance to get one largely just for this task (especially if you plan eventually to replace the chainset with a square taper model), and given that (IIRC) you don't have carbon fibre components on your bikes for which you would also want a torque wrench. I think that the Hollowtech II design offers more scope for - and is less tolerant of - incorrect assembly, i.e. if you get it wrong it is much more likely that part of it will be damaged or fail prematurely. I think the left hand crank coming loose is something which seems to be mentioned more often in threads about Hollowtech II type chainsets, than reports of loose cranks on square taper chainsets. Once the LH crank is slightly loose on the splines of the axle, terminal damage to the crank seems to follow very quickly.

Even if a torque wrench is used to ensure the correct torque when fitting the LH crank, Shimano's instructions state that the crank bolts should be checked after 100km to make sure they have not loosened, by using the torque wrench to tighten them again, and that they should be checked periodically thereafter. It is not a design that is as tolerant of neglect as square taper.

If you don't get a torque wrench, I think you would need to check the tightness of the bolts at much more frequent intervals, at least to begin with, e.g. the first ride after assembly check it a number of times mid-ride, and possibly as often as post-ride for every ride thereafter for a while, and then maybe once a week or month depending on how often you ride that bike.
Post Reply