Shimano Hollowtech-II Crank Spacer

thingiverse

This is a crucial component for adjusting the Q-factor on a HollowTech-II MTB bottom bracket, allowing a reduction of 2.5mm to 7.5mm by eliminating one or more outer bearing spacers. The spacer fits snugly over the end of the crank spindle and enables the "fixing bolt" to apply even pressure against the crank arm via the spacer, ensuring proper pre-loading of the bearings. To achieve a Q-factor as low as 2.5mm narrower, some inner splines inside the crank arm need to be removed. I successfully modified mine by drilling 0.2 inches (5mm) deep with a 15/16-inch drill bit and then smoothing out the remaining splines with a Dremel bit. This adjustment allows the crank to press further down onto the spindle splines, but it prevents the "fixing bolt" from making contact with the outside of the crank. Now, I run my MTB bottom bracket with no spacers at all, resulting in approximately 170mm Q-factor between the outer faces of the cranks. This configuration also gives me a 45mm chain-line on the front triple crank, reducing chain angle in the small/front - large/rear combination. The spacer and fixing bolt can be easily removed once the crank clamp bolts are properly torqued down, which helps minimize the risk of shoe rubbing against the protruding fixing bolt.