External BB advice

[Dogtrousers]

I was sorting out my stuff for tomorrow morning, checking tyre pressures and so on, when I noticed that my cranks weren't turning freely. There's no graunch or bind feelings in the bearings, but if you shove the crank backwards it doesn't spin at all, it just stops. As if the BB contained a thick, damping treacle, or something.

It's a SRAM Apex chainset with SRAM GXP BB. A very modern thing, that I've never dealt with before. Time for some research.

I thought it probably just needs the preload on the bearings setting or some other tweak. So, off I go to youtube and watch a couple of videos and now I'm baffled. There doesn't seem to be any adjustment you can do to it. Assembly seems to be a case of putting it together and tightening it up. No setting of bearings at all.

So what should I do? I don't have the tool for removing the cups, so first step will be get one of those. But in the meantime ... advice sought. And I'll be riding my trusty old-fashioned bike tomorrow.

The bike is still relatively new and has done only a couple of thousand miles. It has been leaning against a radiator and we switched the heating on a week or so ago (well, my wife did).

 

[Moodyman]

Check the preload cap - usually a black cap on the left crank. Should just be finger tight - if it's more than this then it's too tight.

 

[Levo-Lon]

Is this happening with the chain off so its able to spin free? And cranks spin fine forwards.

if its with chain on its worth checking the wheel for a tight free hub..or the mech

as you say the sram cranks just tighten up and no preload adjustment like shimano etc

 

[Dogtrousers]

Check the preload cap - usually a black cap on the left crank. Should just be finger tight - if it's more than this then it's too tight.

Thanks, but it doesn't seem to have such a thing, nothing with any subtlety of adjustment. It seems to be a case of tighten the cups in the shell (5&6 in the diagram), put the cranks together (7) and tighten the crank bolt (8). It all seems to be brute force tightening.
I'm feeling nostalgic for cup&cone.

 

[Dogtrousers]

Is this happening with the chain off so its able to spin free? And cranks spin fine forwards.

if its with chain on its worth checking the wheel for a tight free hub..or the mech

as you say the sram cranks just tighten up and no preload adjustment like shimano etc

No, stiff with the chain off too. Smooth, but not free.
I'm a bit annoyed because it's not done that many miles.
I've found a good SRAM doc here. Looks like it's tool buying time.

And this is an improvement on ye olde cup and cone how, exactly? Just a lot more complicated.

 

[Cubist]

No, stiff with the chain off too. Smooth, but not free.
I'm a bit annoyed because it's not done that many miles.
I've found a good SRAM doc he.re Looks like it's tool buying time.

And this is an improvement on ye olde cup and cone how, exactly? Just a lot more complicated.

What you are describing sounds like bearing resistance which is pretty typical in external BBs when brand new, overloaded, or when the grease has become contaminated.
SRAM Gxp don't have preload adjusters like Hollowtech, so you can discount preload. . Before you go and buy expensive tools to remove the cups try regreasing the bearings which can be done in situ. All you need is an8mm hex key to remove the cranks via the self extracting side.

As it says in the service doc, you can remove the bearing seals with a seal pick. They suggest wiping the old grease out with a rag, but I'd suggest you flush it out with GT85 using the straw to do the job. That way you'll be able to see whether the bearings are damaged. Once it's al nice and clean, a decent quality grease applied with a syringe or grease gun will ensure you have the right amount of lube in the bearings GS. Pop the bearing seal and the outer shields back on and that it, job done.

I find bearing resistance to be surprisingly high on external BBs as compared with an internal system, especially when new or newly greased. The pedals don't whizz round like they do on a nicely bedded in internal BB, but they are easier to maintain and service.

 

[Pale Rider]

Without wishing to state the obvious, make sure the solvent in the GT85 has dried/evaporated before you apply the new grease or you will end up with a slimy mess.

Doing the job in a warm room and taking time with the dry rag will do it.

 

[Dogtrousers]

Excellent, thanks for the advice guys. I'm slowly easing myself into the 21st century.

 

[Dogtrousers]

Not going well I'm afraid. I finally got around to doing the maintenance, all by the book... right tools and stuff, no bodging.

The drive-side bearing is completely seized. Non drive side turns free as you like.

To explain what I mean, the bearing has an inner collar that takes the axle, which sits inside the bearing race. (Arrowed in the picture). On the drive side I can't shift it at all. It's stuck fast. I can't move it at all. To begin with I was baffled as nothing would turn. I couldn't figure out what was meant to bear on what. . It was only when I looked at the NDS that I realised which part was meant to turn. Obviously it's not an easy thing to grip but with finger strength I can't turn it at all.

The service document says "do not remove retaining clip". So all I can do is clean and re-grease, and that's not going to do a darn thing. It seems to be a case of "no user serviceable parts inside"

Does this mean I need to buy a new BB? This one has done at most 2,000 miles.

That's not good. I think I'll drop Spa a line (It's a Spa bike - and still quite new) see what they say.

 

[ayceejay]

From the outside both bearings look the same and if you put a finger in they should both move as you slide your finger around if one doesn't it is knackered.
In picture number 2 in your graphic above you can see 2 washers, tone at either extreme, in my experience it is easy to loose one of these because it is not fixed. If one of these is missing that would explain why your bb has failed.

 

[Dogtrousers]

From the outside both bearings look the same and if you put a finger in they should both move as you slide your finger around if one doesn't it is knackered.
In picture number 2 in your graphic above you can see 2 washers, tone at either extreme, in my experience it is easy to loose one of these because it is not fixed. If one of these is missing that would explain why your bb has failed.

Cheers. Those 2 extremes are the outer seals. They're both still there. But the drive side wotnot is rock solid.

I'm not a happy chap. I'm restraining myself from a rant about the good old days.

 

[ayceejay]

Another thought: on the plastic barrel that the axle passes through there should be an arrow pointing to and words telling you which is the drive side, now I am not even sure that this is possible but if this went in the wrong way ????
The GXP bb is not very expensive but it should last longer than the 2000 miles you quote - see what Spa has to say although you have probably voided the warranty by taking it apart.

 

[Dogtrousers]

Thanks for your help everyone.

I bought a new BB. Installed it, carefully following the instructions, and all is well. The only equipment I didn't have was the rubber mallet, so I used a lump hammer and postitioned a Ken Hom Chinese cookery book to soften the blow, then hit it. The sound went WOK WOK. As luck would have it I hit a flooded road on my first ride which soaked both my feet and lapped the BB. Hope it's OK!

Anyway, I'm still pretty peeved about this. I didn't consider BB design when choosing my new bike. I'm now utterly baffled as to why external BBs were invented when they seem inferior to the sealed unit (and their predecessor the cup-n-cone). I guess they must be lighter, with the hollow axle and all?

 

[ianrauk]

My external BB's seem to last a heck of a long time. Think I have only ever had to change one over a period of 10 years because of wear. When you fitted it, did you smear the plastic seal with grease? That always help's to keep the muck out.

 

[Dogtrousers]

My external BB's seem to last a heck of a long time. Think I have only ever had to change one over a period of 10 years because of wear. When you fitted it, did you smear the plastic seal with grease? That always help's to keep the muck out.

Thanks Ian, that's reassuring.

I didn't fit the original (was a new bike) but this one I put plenty of grease on all of the indicated points, round the seals etc. As it's my new posh bike I even shelled out for some fancy expensive grease that came in a tube (a tube!! like toothpaste! not a tub or a tin ... what is the world coming to?).

Maybe I was just unlucky and got a lemon last time. I'll try to take the old one to bits some time to see why it siezed. It's really stuck fast.