Bottom bracket - symptoms and diagnosis of impending failure

[wafter]

I've never done sufficient mileage on one bike to experience a BB failure, however..

I've become aware of an oscillation / rumble felt through the pedals on each "power" stroke, typically at higher loads / lower cadence. There's no tangible noise associated with this, while the crank feels smooth to rotate by hand unloaded (as much as one can tell with a chain fitted) and there's no detectable end-float, rock or other movement that I can feel.

The BB is a Shimano *EDIT* BB50 *EDIT* on about 10k miles in my ownership and an indeterminate amount prior to this; from tyre wear I'd reckon maybe another 5k so it owes me nothing.

I'm thinking the acid test would be to remove the crank and manually rotate each bearing to check for roughness and play; which I'll do once I've recovered the necessary tools. In the meantime I'm interested to hear any other thoughts on diagnosis, lifespan and potential failure modes as I need to use the bike but I don't want to end up stranded..

Cheers

 

[chriswoody]

Personally when I start to feel the symptoms you describe, I just unship the chain from the chainrings and loop it round the bottom bracket shell or just take the chain off completely. Then I'll just rotate the cranks using my fingers on the crank arms to make sure I'm not feeling the pedal bearings. That's normally enough to tell if the bearings are running rough.

As you say, the acid test is to take the cranks off completely and feel each bearing with your fingers, but I've been able to feel it through the crank arms as well.

 

[wafter]

Personally when I start to feel the symptoms you describe, I just unship the chain from the chainrings and loop it round the bottom bracket shell or just take the chain off completely. Then I'll just rotate the cranks using my fingers on the crank arms to make sure I'm not feeling the pedal bearings. That's normally enough to tell if the bearings are running rough.

As you say, the acid test is to take the cranks off completely and feel each bearing with your fingers, but I've been able to feel it through the crank arms as well.

Thanks - your post has goaded me into pulling my finger out and whipping the chain off - which was nice and clean thanks to the wax (would have been a good opportunity to check the BB when swapping the chains earlier in the week, but not to worry..).

Rotating by hand there's the slightest bit of roughness detectable, especially when applying some force in the direction of load during pedalling, so I suspect that's fairly conclusive.

I have a used apparently-good one that can go on as soon as I've recovered it and the tooling from the homestead at the weekend

 

[Fastpedaller]

Another 'test' I've found to useful.... whilst riding and aware of the issue, placing finger(s) on the seat tube or downtube, the 'roughness' can be felt. I've had various BB's over the years that have given huge service, or minimal service, so it can be a lottery. A Shimano bb55 (rated as great by many) started clicking after about 1000 miles, yet others have lasted over 40000 miles.
last year I decided I'd 'improve' a new cartridge BB on one of the bikes by adding some grease- I did this before fitting the unit. I moved the internal sleeve and carefully removed the inner seals of each bearing, cutting them and removing them to the rubbish bin. More grease was applied using a thin wooden coffee stirrer, and the sleeve put back into position. After a few months I had clicky bearings! It seems the grease had moved into the sleeve and the bearings were virtually running dry - the seals do keep the grease in! Lesson learned...... I replaced the bearings with new ones, but this time (as I was removing the old bearings), I carefully picked the inner seal off each bearing, added some grease and then refitted the seals - no damage done and some extra grease, as the bearings come with little grease and are intended for high-speed use (not bicycles). I expect them to last many years. On the Cycling UK forum there are many tips for extending the life of BB and wheel bearings.

 

[fossyant]

They can get grumbly or develop play. Although if SRAM GXP, they can just seize after a wet ride - they aren't 'good', hence running a Praxis GXP on my MTB.

Pop the chainset off and rotate the bearings by hand.

 

[wafter]

Thanks folks.

Typically with all that's gone on over the past few weeks I've not yet gotten around to replacing the BB. As it stands the rumble is faint and I hope if I continue to use the bike the BB shouldn't fail catastrophically (although @fossyant's tales make a me a bit more anxious; despite the fact mine's a Shimano item).

I did see a video a while ago on the subject where the same BB (EDIT: BB50) showed enormous play (maybe 1-2mm) between the inner and outer races and mine certainly has a long way to go before it gets that bad

 

[Fastpedaller]

looks like SRAM GPX is an external bearing, so not square taper. The chance of a catastrophic failure with a square taper is very remote.
ETA after googling.... yours is an external bearing one, of which I have no experience

 

[fossyant]

looks like SRAM GPX is an external bearing, so not square taper. The chance of a catastrophic failure with a square taper is very remote.
ETA after googling.... yours is an external bearing one, of which I have no experience

Wafter has a Shimano Hollowtech which are generally quite reliable

 

[fossyant]

Cheapy cheap

https://www.merlincycles.com/shiman...F0qtqgSoj1h6PVM80z7EzZSP0WFZb5mRoC0rEQAvD_BwE

 

[ColinJ]

The chance of a catastrophic failure with a square taper is very remote.

I had it happen once, many years ago. I can't find a post about it here so I might have posted about it back in my CyclingPlus/BikeRadar days.

I can't remember much about it other than I ignored warning signs for a few rides and eventually wished that I hadn't!

 

[wafter]

Wafter has a Shimano Hollowtech which are generally quite reliable

Yup; as much as I seem to spend most of my life complaining, I certainly have no cause to whinge relative to the performance I've had from this unit

Cheapy cheap

https://www.merlincycles.com/shimano-mt500-press-fit-bottom-bracket-218420.html?utm_campaign=googlebase-GB&utm_source=googlebase&utm_medium=shopping&utm_term=MTB+Bottom+Brackets+&+Cups&ucpo=135752&gad_source=1&gad_campaignid=18448572153&gbraid=0AAAAAD_kj5-bDtqfdk2ZIE3xNnVZN7zxF&gclid=CjwKCAjwirLWBhBBEiwAlItbEs3pYyZya-sZE0ir1BuxdnF0qtqgSoj1h6PVM80z7EzZSP0WFZb5mRoC0rEQAvD_BwE

Press fit - how very dare you!

Thankfully I have another spare BB50 that came with a used crankset so that can go in.

On the new bike I'm switching to the posher BB-MT801 as these look nicer and are smaller (so work better with my crappy hard-anodised-I-love-to-scratch-things-but-am-actually-soft-as-shoot Park BB tool since I can use it with a much more sympathetic plastic insert / reducer) while the last one I got in for the parts bin cost me something like £11.50

 

[fossyant]

Yup; as much as I seem to spend most of my life complaining, I certainly have no cause to whinge relative to the performance I've had from this unit


Press fit - how very dare you!

Apologies, should have linked to the threaded one ! whoops.

 

[wafter]

Apologies, should have linked to the threaded one ! whoops.

Not to worry - appreciate the thought

It's a bit mental how little you can pay for good quality consumables from some places now!