Yesterday I was installing a BB-MT501 HollowTech II bottom bracket into my ~2006 Trek 520 frame. This frame has a 68mm BB shell.
I was following the directions on Shimano's website: https://si.shimano.com/en/dm/LAFC001/install_remove_bottom_bracket
- Bike frame BB shell was chased and faced by LBS
- Cleaned out and dried BB shell
- Applied light coat of grease to BB shell threads and to the BB cups
- Used a 2.5mm spacer on the non-drive side and 1.8+0.7+2.5mm spacers on the drive side.
- Threaded in both cups by hand almost all the way to ensure there is no cross-threading
- Used a calibrated high quality torque wrench (Precision Instruments) to torque the non-drive side to 26lb-ft which is on the very low end of the 35-50Nm given by Shimano.
- Used the same torque wrench to torque the drive side.
I was able to torque down the non-drive side successfully but when torquing the drive-side, both the 1.8 and 0.7 spacers cracked.
What did I do wrong?
I took everything apart and it doesn't look like the BB shell or the actual bottom bracket was damaged. Thankfully.
What should I do now? I'm thinking it might make sense to have metal spacers instead of plastic but I don't know if those exist.