Installing HollowTech II Bottom Brackets

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The new style external bearing bottom brackets are challenging to work with at times. Take the time to measure each part of the assembly to make sure that everything will go together as planned.

Sometimes the Bottom Bracket Shell is Too Narrow

While this example is for a bottom bracket shell that is less than 68mm, the same solution is true for one that is less than 70.5mm or 73mm.

Please excuse the dirt and filth on the parts in this discussion. I was in a ghetto mood, but the result of the work was clean enough for great results.

Measuring the bottom bracket shows that it is well made and will install perfectly for a bottom bracket shell width of just over 68mm with 2x 2.5mm shims.
Hollowtech-II-1.jpg

The two shims. They will be mounted on each side of the bottom bracket shell to space the pedals evenly and attain the final chain line, 50mm.
Hollowtech-II-2.jpg

The bottom bracket shell is 67mm, 1mm short of optimum 68mm. This is a result of the amount of matirial necessaryly removed to properly face the shell.
Hollowtech-II-3.jpg

A 1mm shim needed to be installed on the drive side to correct for the short bottom bracket shell.
Hollowtech-II-4.jpg

Just 1 2.5mm shim on the non-drive side.
Hollowtech-II-5.jpg

The crank installed with proper bb spacing, chainline, and pedals centered. The crank should spin freely.
Hollowtech-II-6.jpg