Shimano Hollowtech experience anyone?

[eljost]

Adding to this old thread. I recently (last week) had the experience of my Shimano Hollowtech BB fail on my after 2500 miles. It broke along one of the thread just inside the BB on the right crank arm side. The left side was fine. My bike was loaded with 30 lbs of gear (front and rear total) and I weigh 165 lbs.

I rode 25 miles on it that way to get to the next town. It was able to be fixed, but made me question the integrity of the product and/or bike. I'd asked a couple bike shops about it and they had never heard of such a thing happening. The BB was factory installed. I suspect it was poor installation at the factory, but I can't confirm. The mechanic who repaired it made no mention of a poorly faced BB shell, but I didn't ask either. He was baffled as well. It has made me consider changing to a more robust (old school) BB. Judging by the posts in this thread, I tend to believe the Shimano product was probably fine, but installation was not. 

[PeteJack]

See if any advice here gives you a clue https://bikemagic.com/how-to/mountain-bike-maintenance/fitting-hollowtech-ii-cranks.html
My WAG is that something has been overtorqued.at the factory, other than non-parallel BB faces  there's not much else it could be. Hambini has more to say about bottom brackets than you'd ever wish to hear. Good luck.

[DaveB]

Adding to this old thread. I recently (last week) had the experience of my Shimano Hollowtech BB fail on my after 2500 miles. It broke along one of the thread just inside the BB on the right crank arm side. The left side was fine. My bike was loaded with 30 lbs of gear (front and rear total) and I weigh 165 lbs.

I rode 25 miles on it that way to get to the next town. It was able to be fixed, but made me question the integrity of the product and/or bike. I'd asked a couple bike shops about it and they had never heard of such a thing happening. The BB was factory installed. I suspect it was poor installation at the factory, but I can't confirm. The mechanic who repaired it made no mention of a poorly faced BB shell, but I didn't ask either. He was baffled as well. It has made me consider changing to a more robust (old school) BB. Judging by the posts in this thread, I tend to believe the Shimano product was probably fine, but installation was not.

Yours is truly an unusual failure.  Most of the complaints are of bearings getting rough and developing play over time and miles, not an outright fracture.  Out of curiosity, was your broken bottom bracket actually a Shimano unit?  It's common for bike companies to spec lower cost off-brand components where they aren't easily seen?

As a follow up to my earlier post from 2016, the two HTII bottom brackets I reported as having 10,000 miles each at the time are still in service with 24,500 and 22,800 miles respectively and with no signs of problems. 

[staehpj1]

The design of the old square taper bottom brackets is such that if maintained they can last pretty much for ever.  They also fail slowly and with plenty of warning.

Just by the nature of the type of bearings in them, neither of those points are as true of the newer designs.  The newer designs have other advantages though.  They are lighter and easier to work on IMO. You can carry spare bearings for the ones new easily enough.  While the parts last forever unless really badly neglected square taper require more tools and skill to get assembled and adjusted correctly.

[DaveB]

You are describing the now uncommon separate spindle, cup-and-cone bearing bottom brackets.  Yes, good ones like Shimano, Campy and the better Suguino models could indeed last nearly indefinitely if (big IF) properly maintained and adjusted.  The problem, was they required routine maintenance, an involved tool kit and were a bit finicky to adjust correctly.  Most died from neglect.

The vast majority of surviving and currently available square taper bottom brackets are cartridge units which are pretty much install-and-forget until worn out.  The good ones have an excellent reputation for durability but aren't repairable with the exception of Phil Wood ($$$$) bbs.

The first non-square taper bottom brackets to see common use were the Shimano Octalink (Hollowtech I) and ISIS hollow spindle, splined interface cartridges. They were both lighter and stiffer than square taper designs.  Both got a poor reputation for durability due to the smaller bearings needed to allow the larger spindle diameter.  Most of the ISIS units deserved it but the HT I cartridges did not.

The answer to small bearings was the external bearing bottom brackets  like HTII and its competitors.  These were even lighter and stiffer but caused concerns that the bearings were more exposed to the elements.   They also made more demands on bottom bracket shell alignment.  These bottom brackets have pretty much proven them selves over the years and complaint about premature failure are no longer common.

[staehpj1]

Yes, good ones like Shimano, Campy and the better Suguino models could indeed last nearly indefinitely if (big IF) properly maintained and adjusted.

True that for many the maintenance won't be done.  That said over the last 50+ years I have worked on dozens (scores?) of square taper bottom brackets and never had one that I couldn't revive to meet the standards of the owner.  I grew up where we had to make due with what we had so sometimes back in the day that meant the crude technique of running in the bearings in with some valve grinding compound to clean up the pitted cups and cones on a neglected bearing before cleaning up and repacking.

By the way my personal preference runs toward the newer styles these days.  I just recognize the advantages of both.

[eljost]

Yours is truly an unusual failure.  Most of the complaints are of bearings getting rough and developing play over time and miles, not an outright fracture.  Out of curiosity, was your broken bottom bracket actually a Shimano unit?  It's common for bike companies to spec lower cost off-brand components where they aren't easily seen?

As a follow up to my earlier post from 2016, the two HTII bottom brackets I reported as having 10,000 miles each at the time are still in service with 24,500 and 22,800 miles respectively and with no signs of problems.

The BB I had was a Shimano SM-BB52. It had two spacers on the drive side. I checked other bikes and that seems to be a pretty common BB as well as the double spacers.

[David W Pratt]

Eljost, your failure sounds to me like it might be a combination of the following, in no particular proportions.  Fatigue caused by a couple of adjacent bearings being ever so slightly out of line.  Thus the axle flexed just a tiny bit every revolution.  A stress concentration caused by too deeply cut thread.  If the out of line bearings kept flexing the shaft and the stress riser notch of the thread was in the right place you might have a perfect storm of bad luck.

[eljost]

It definitely felt like a perfect storm of failure.