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Hollowtech bottom bracket durability

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Hollowtech bottom bracket durability

Old 04-12-21, 09:03 PM
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dwsmartins
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Hollowtech bottom bracket durability

After migrating from square tapered to external bearings (Shimano BB-UN26 to Shimano SM-BB52, always from authorized local distributors, so original parts) I’m having doubts about the durability of the Hollowtech ones.

The UN26 was installed in 2011 and lasted more than 12000km until August 2020, when a tiny play developed. I got an used FC-M542 crankset and was eager to install it: bought new chainrings and a SM-BB52 bottom bracket to put on use.

It was installed by the manual: one 2,5mm spacer on the non drive side, three spacers (a 2.5mm plus a 1.8mm and another 0.7mm) on the drive side; tightened to 35Nm, but took it to 50Nm as it creaked somewhat (all inside limits). Haven’t faced the shell, though.

For my surprise, the drive side cup broke right on the thread after just about 3 months. Claimed the warranty, but had to buy and install another one while the distributor verified the failed one, which took about three months due to COVID.

The second bottom bracket was installed by the mechanic who sold it to me, and I really trust him. He’s very experienced and careful, even doing it in front of me.

To my despair, after a hard climb or two, the bottom backrest starts to make some clicking noises, always on the down stroke, first just on the drive side, then after a while on both. We (the mechanic and me) already ruled out everything we could think of. The noise vanishes when we disassemble and reassemble the crankset, but it comes back after a hard climb. And my area is full of hard climbs...

I’ve already noticed it has to do with play between the axle and non drive side arm. The plastic nut used to adjust preload was replaced, as well as the Allen screws. The pin used to lock the non drive side arm is OK. Are we missing something here? What do you think?
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Old 04-12-21, 09:28 PM
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Hollowtech bottom brackets are pretty bombproof in my experience. I use them on all but one of my bikes, and have only had to replace the BB on my 520. I think i got over 10,000 miles of all weather riding before replacing.
Even after 2 pretty brutal winters and 6 or 7000 miles on my winter/rain commuter, the hollowtech BB is still going strong.
I tend to replace square taper cranksets with hollowtech units because they require so little attention. I remove the crank and cups once a year as part of a maintnence schedule and to grease the threads and spindle, but even that probably doesn't need to be done to be honest.

You aren't missing a spacer behind the outboard bearing cup, are you? That would prevent the preload cap from being able to take all of the play out of the cranks when attaching the non-drive crankarm. The crankarm will instead bottom out on the splines of the spindle before it gets sufficient preload on the bearings.

Last edited by SalsaShark; 04-12-21 at 09:36 PM.
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Old 04-12-21, 09:35 PM
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The Hollowtech units are probably the best of the external BB system designs for 68mm BSA shells.

You mention not having the shell faced. The new BB/crank systems are less tolerant of out of spec shells--did your wrench check/face it?
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Old 04-13-21, 08:30 AM
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12 years ago I left square tapers for HollowTech II and other similar 2 piece cranks with their external bearings and never looked back. Have not replaced any yet or had a single issue with crank or bb.

As always with anything YMMV. Somebody has to be the one in a million or what ever the failure standards are. I guess that it is just in your cards for it to be you.
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Old 04-13-21, 08:48 AM
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+1 for the suggestions of checking spacers and BB shell facing. As for maintaining a HT bb you can just use a thin blade to remove the seals, flush and re-lube and it should last for many, many miles. You can even do this while it's still on the bike but of course it's good to remove the BB and grease the threads every so often to prevent corrosion. Mine has 26K miles on it and feels like new. You also mentioned the crankset was purchased used. Has it been carefully inspected for any issues such as the axle coming loose from the DS crank or a microscopic bend or bearing surface ovalized or not perfectly smooth?
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Old 04-13-21, 08:00 PM
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Haven't had any issues on mine though most of my stuff uses Wheels MFG Shimano compatible stuff but I do have a bike with a used Tiagra Hollowtech II B.B. and I have had it for 6 years at this point with zero issues and it was probably 5 years old at that point when I got it and it is friggin' cheap Tiagra.
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Old 04-14-21, 06:55 AM
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Guys, thanks for the replies. Your answers have pointed some possibilities:

* Neither I or my mechanic faced the bottom bracket shell. Maybe this could solve this riddle, but don’t know any wrench who does this in my area. Let’s see if I can find one...

* Crankycrank has mentioned the axle might come loose from the drive side. In fact, it’s coming loose from the non drive side, where the left arm holds it on the spindle. The Allen screws are correctly torqued, should it worth the risk of applying more torque on them?

* Also, the crank has been inspected: no ovalization, just a slight mark on the bearing contact points, barely visible, not detected on the digital caliper (0.05mm precision). Maybe it’s detectable on a micrometer, but if it’s that sensitive it shouldn’t last as long as other fellows report. I am right assuming this?

* About the small plastic tab with a pin, the one who gets into a hole on the spindle, on the non drive side (I guess I can’t describe it better than this): it doesn’t even bent, despite the fact the non drive side arm sliding out. The hole is somewhat large for the pin, so maybe there’s some tolerances allowable. Is it really like that?

Thanks in advance for any answers!
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Old 04-14-21, 07:42 AM
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We see a somewhat greater wear rate w/ external BB bearing designs, compared to threaded cartridge units. Not a deal breaker though for us or our customers. Andy
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Old 04-14-21, 08:20 AM
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Originally Posted by dwsmartins
Crankycrank has mentioned the axle might come loose from the drive side. In fact, it’s coming loose from the non drive side, where the left arm holds it on the spindle. The Allen screws are correctly torqued, should it worth the risk of applying more torque on them?
If it's coming loose there is definitely something wrong if the bolts are correctly torqued. The first thing I can think of off hand is possibly the bolts have been replaced with the wrong type and they're bottoming out on a too long bolt shoulder or the washer is missing. Easy to check by looking through the clamp slot though. Also run the bolts from the outside to check for damaged threads causing false torque readings.
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Old 04-14-21, 09:21 AM
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The creaking on my integrated spindle bottom bracket completely went away after retorquing the outboard bearings.
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Old 04-15-21, 06:28 AM
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dwsmartins
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Originally Posted by Crankycrank
If it's coming loose there is definitely something wrong if the bolts are correctly torqued. The first thing I can think of off hand is possibly the bolts have been replaced with the wrong type and they're bottoming out on a too long bolt shoulder or the washer is missing. Easy to check by looking through the clamp slot though. Also run the bolts from the outside to check for damaged threads causing false torque readings.
Seem like this might be the answer! I was studying the exploded views on Shimano’s technical documents site and remembered just right now the two Allen screws where replaced and the washers removed due to the new screws having a larger head. When I’ve put my hands on this crankset it had just one of two washers, possibly not even an original one.

If the original washers are splitted, like this:

It should serve the purpose to prevent losing tension, right? If that’s the case, maybe this is the root of my troubles!
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Old 04-15-21, 08:10 AM
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Originally Posted by dwsmartins
It should serve the purpose to prevent losing tension, right? If that’s the case, maybe this is the root of my troubles!
Yes, this could be a problem. I'm not sure if a lock washer is correct for every HT crank as some, if not all, have flat washers. Some of the OEM bolts are model specific and include washers. EV-FC-M542-2681A.xls (shimano.com) Also make sure you have the axle washer (#5 in the diagram) in place as they can sometimes go missing when the crankset is removed.

Last edited by Crankycrank; 04-15-21 at 08:24 AM.
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Old 04-16-21, 11:29 AM
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Maybe I am reading this wrong but I have 24mm Shimano 6800 cranks with external BB. I have 23,000 miles on them and they spin like a top. I have never touched them. On all my previous bikes I have used external bearing BB with Shimano Cranks. These include 6600, 6700, and 7800 durace, and never have had to replace or service a BB on any of those bikes. They are HT cranks right? In fact I plan never to buy a bike with press fit BB due to the inherent problem that seems to be, although some have done better that others, never will they exceed the external threaded BB for ease of use.
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