Shimano external BB bearing cups

[FaustoCoppi]

What length of service life should I expect? Last year I covered 7.5k miles in most types of weather, I replaced my external BB as I was detecting a roughness in the pedal stroke, that sorted the issue, now I’m currently using my Brevet on an elite turbo, yesterday I noticed a scrunch just behind TDC on the stroke mostly coming from the drive side, I eliminated pedal as an issue by temporarily swapping out a replacement pedal, so I’m assuming it’s the bearings again, but really 7.5 k miles, surely they should last longer? What are other’s expectations/ expectations with lifetime of this particular shimano part? I’m considering going to Hope bearings, but will they be any better?

[FaustoCoppi]

SM-BB52 Deore MTB sealed bottom bracket outboard bearings are the specific part if this helps...

[Danneaux]

Most external/outboard bearing bottom brackets' lifespans are very sensitive to preload and Shimano units are no exception in my experience. Be mindful to observe the recommended torque on the instructional flyer included with each unit. I generally fit my left arm without any preload, just pressing the end by hand until I get contact, then checking for any residual play or stiffness, then tighten and finally fit the preload adjuster, but not everyone does it that way. The main thing is to avoid getting the preload too tight, as that will compress the bearings and lifespan will be shorter. A friend overtorqued his on installation and it was finished just before 1,500mi/2,400km.

In my experience, Shimano OBBs's lifespan is also dependent on weather and conditions -- rain and dust can penetrate the seals, which I have not found to be very robust. The units are fairly easy to take apart and those I've seen inside were equipped with surprisingly few ball bearings and little grease, which can't have helped lifespan much. Fortunately, these units are pretty inexpensive to replace.

There are rebuild kits available (Google search) or you can DIY, as shown here:
https://www.instructables.com/Hollowtech-2-bearing-change/
...and...
https://www.instructables.com/Holowtech-2-bearing-change-2/
If you can install some good cartridge bearings and then pry off the seals and pack well with grease, you can restore function and have a reliable unit for longer than the original. I prised off the seals and repacked the bearings on an original Deore unit with Phil Waterproof grease before installation and it has far outlasted the stock OEM unit that preceded it. The full load of grease helped lubrication and prevented entry of water and dust.

I preferred to replace the Deore unit on my Nomad with a Phil Wood unit. It was packed with Phil Waterproof grease, had a full complement of high quality cartridge bearings and the shells and sleeved spacer are robust stainless steel. It is expensive but so far mine has outlasted several Shimano units and shows no signs of failure. It is hard to predict lifespan in advance, but I surely would not be surprised if it easily managed 20,000mi/32,000km under all-weather touring conditions.

You can download some photos of mine as I installed it in my Nomad here:
http://thorncyclesforum.co.uk/index.php?topic=4523.msg43281#msg43281 ...and in the several posts after.
Sorry, you'll have to download the photos to view them as the thumbnails were corrupted/lost during a Forum software upgrade.

By their very design, OBBs tend to have a shorter lifespan than those with internal bearings (which typically also have a square taper on the spindle). I have several Phil internal units with well over 35,000mi/56,000km that are still going strong. In contrast, I think your present Shimano Deore OBB unit gave reasonable service "in all types of weather" based on my experience and those of people I know and whose bikes I have serviced.

Best,

Dan.

[martinf]

Maybe off topic, but I get very good service life from traditional square taper bottom brackets fitted with additional seals.

I use V-rings that I fit behind the crank arms, held by a stack of O-rings so they are in a position where they rub slightly on the face of the bearing cup.

This only works with some bottom brackets.

So far the longest-serving I have had was a TA cup and cone bearing set at just under 40,000 km.  I had also modified this with a sleeve and grease nipple for easy lubrication, but I reckon the most important feature was the seals keeping out muck and water.

I have several TA Axix bottom bracket units with cartridge bearings still in service, the extra external V-ring seals I fit significantly extend the life of the (fairly cheap and easy to replace) cartridge bearings. 

V-rings don't work well with the Shimano UN series bottom brackets that I use on some of my Thorn frames, so I bought a small stock of these units at clearance prices.

[FaustoCoppi]

Thank you both, various on line forum ‘investigations’ suggest that the part is not built with longevity in mind, I have had Shimano outboard BB on many bikes over the years, just lately though I have noticed that the quality isn’t as good and service life significantly reduced as a result, probably a deliberate decision on the part of the manufacturer’s?
I think I’ll replace them with a pair of Hope engineering BB bearings which are readily serviceable.
Thank you both again for your advice and suggestions.

[spokenword]

I used to suffer short service life but since I found that you can remove the dustcap and re grease the bearings they seem to last 20-30,000 km. There are instructions of how to do this online.

[Andre Jute]

I've always had excellent service from old-fashioned Shimano square bottom brackets. But this thread makes me wonder whether the life of the Bafang electric midmotor on my bike will be limited by the seals in the bottom bracket, which is an integral part of the motor used to hang it on the bike by the bottom bracket shell.

As if the winter and the pandemic isn't depressing enough...

On close investigation it turned out that the life of my first, different, electric motor was limited not by the plastic gears melting, as I thought at first, but by the lack of adequate heat dispersion around the electronics in the control box. So, on inspection and general principles when I fitted it, I was right that heat would be its greatest enemy, but misidentified the first and final failure the heat would cause; others did in fact on that model suffer melted plastic drive gears, and replaced them with aftermarket steel gears to good effect. I didn't mind replacing that motor: I bought it as an experiment to establish parameters for a longer-lasting installation, and knew in advance that it wouldn't survive too many years on the hills in my countryside, and that even a perfect electric motor/control installation would eventually fail.

Still, the current motor on my bike, on which everything is larger to account for larger than average use, has already lasted twice as far as the motor that self-destructed. But it would be a shame if an installation otherwise so pleasing is terminated by an inadequate seal costing perhaps pennies at the factory door. That's not the sort of thing I shrug off with, "I don't mind."

***
One of the signs of encroaching age is, "I can remember when everything on a bicycle lasted forever." Actually, it didn't. People used their bicycles less intensively and serviced them more often. The outlook, and the bike's economic place in the owner's worldview, were entirely different to what they are now.

[JohnR]

One of the signs of encroaching age is, "I can remember when everything on a bicycle lasted forever." Actually, it didn't. People used their bicycles less intensively and serviced them more often. The outlook, and the bike's economic place in the owner's worldview, were entirely different to what they are now.

My memory is that the bikes in those days were more maintenance friendly. I used to clock up about 2500 miles per year going to/from school and would periodically put some oil into the appropriate holes provided on front axle, bottom bracket and rear hub. Sometime during the summer holidays I would check and adjust the bearings. Manufacturers of these "sealed-for-life" components don't stress that the life concerned is that of the component rather than the user - a bit like the meaningless lifetime warranties which actually mean that when the warranted item dies then the warranty expires.

BTW, I've found that https://baldwinscycles.com/ has some of the UN55 73mm bottom bracket cartridges in stock.

[FaustoCoppi]

I have the hollow tech axle on my Deore crank/chain ring so more reliable longer lived square taper BB not an option, that’s progress for you ! Or a conspiracy by bicycle components manufacturers to constantly ‘improve’ bike components and convince the buying public we ‘need’ these improvements!
Yes ... I’m old and curmudgeonly, and unapologetic too .

[FaustoCoppi]

Strip down, seals removed ( little effort required) . Drive side bearing from where the noise and sensation of roughness was coming, a oily slop was oozing from behind the seals into the inside of the bearing, both sides now re greased with a lithium gear grease, no opportunity to put my ‘repair’ to the test, but hopefully it’s an improvement on a nasty watery oily slop that was in the race.

[FaustoCoppi]

All sorted... for the time being...