Replacing Your Bottom Bracket – FSA Mega Exo / SL-K

There are lots of different types of Bottom Bracket and each require different tools to maintain or replace them.  The type of cranks you have may also require different tools as well and here we are looking at the FSA Mega Exo BB and SL-K road cranks.

Tools Required

Back in the old days (depending on how old you are of course) BBs weren’t sealed units and required regular inspection and re-greasing, popping the individual bearings back into place when you had finished. These days sealed units can’t be maintained so it’s a simple replace and throw away job.  Luckily prices are very reasonable, the Shimano Ultegra BB used here was only £15.  You need the right tools of course, in this case a Park Tools BBT-9 spanner which will work for all Shimano Hollowtech II and FSA Mega Exo BBs.  The FSA crank doesn’t need a separate crank extractor as it’s built-in to the non-driveside crank.


So, first up get your bike on the workstand (if you have one) and start by removing the non-driveside crank with a 8mm hex key.  As you rotate the key it will pull the crank off the splined shaft which is permanently attached to the driveside crank.  Once complete you can unhook the chain and simply pull the rest of the chainset off – simple!

As you can see on our BB there is a good deal of wear to the surface of the bearing case.  Now simply unscrew the BB cups from the frame using the BB spanner.  Spinning the bearings around by hand meant you could easily feel the notchiness and play that led to the decision to replace the unit in the first place.

Remove Cup
Old BB Cup
Dirty BB
Clean BB

An inspection of the BB itself showed a good deal of muck and debris – time for a clean!  You can use any cleaner to do this job, water-based or solvent-based are fine.  You may even need the attention of a wire brush if things are really bad in there.  Once cleaned up apply a good coating of grease the the threads before screwing on the new cups.  It would be difficult to get them on the wrong way around as the threads don’t match and they are marked Left and Right!

Fitting New Cups

Tighten the cups firmly, not with all of your strength but with a good amount of power.  Now is the time to give the area around the BB a good clean – you won’t get the chance to have as good access as this again.  With the FSA crank simply push the driveside crank into place (remembering to ensure the chain can be put back on).  It probably won’t fit flush with the BB but you can give it a tap with a mallet until it is.


Torque Settings

Now switch attention back to the non-driveside it’s time to reattach the crank (make sure it’s in the right orientation) and then slowly tighten the bolt using the hex key until it’s firmly on.  This is the tricky bit, ensuring it’s on tight enough.  The bolt shows a recommended torque setting of 450 -550 Kg-cm (44 – 54 Nm) but most small torque wrenches with hex key fittings don’t go that high.  You can use an automotive torque wrench with convertor or just guess and tighten it up quite a lot!  45nm on an 8mm hex key is quite hard to achieve so give it some oomph.

That’s the job complete.  Be sure to check for play in the cranks before your first ride and again after a hundred miles or so.