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?