To replace the stock 42T with the X-Cog 44T sprocket, first we need to remove the original 42T and then press on the new 44T sprocket.
Installing the X-cog is a bit like cutting the steerer tube on a new fork. A bit scary the first time you do it, but really no big deal if you take your time. If you're not comfortable installing your X-cog, get a professional at your local bike shop to install it for you.
XX1/X1 Cassette Construction
The stock Alu 42T sprocket is press fitted onto the single piece steel 10-36T "X-dome". On the X-Dome there are 18 short pins which press into holes on the 42T holding the 2 pieces together. This pressfit can easily be seen by looking at the back face of the cassette. (Should we have something here about X1 incompatibility and why?)
Step 1 (Slide 1) Remove your XX1/X01 cassette from your bike.
Step 2 (Slide 2,3,4,5) Remove the 42T
Remove the stock 42T sprocket from the X-Dome 10-36T cluster using a flat head screwdriver. Removing the 42T is like opening an expensive can of paint!
Insert the screwdriver tip between the 42T and the 36T sprocket at the junction where an arm of the 42T meets the 36T, as close to the press fit pin as possible (Slide 2/3). Do not try to fully separate the 42T from the 36T with the first screwdriver twist. Gently twist the screwdriver at the first junction and then move clockwise around the cassette gently prying at each of the 18 pressfits. You should aim to do this procedure 3 times (Slide 4), slowly increasing the force, until the 42T sprocket finally disengages from the 36T (Slide 5).
Step 3 (Slide 6,7,8,9,10,11) Aligning the X-Cog 44T
The X-cog must be correctly aligned with the X-dome before assembling so that the shifting features of the 44T are correctly aligned with the 36T.
One of the 18 pressfit pins on the X-Dome is slightly wider than all of the others (Slide 8). On some models of cassette the largest pin has a groove to make identification easier (Slide 9).
Insert this pin into the hole onto the X-Cog (Slide 10) identified by the laser etched arrow (Slide 7). All of the 18 pins should now be sitting on the holes on the X-cog (Slide 11)
Step 4 (12,13,14,15) Press fit the X-Cog onto the X-Dome
Place the X-cog assembly onto a flat wooden surface (Ideally not your Mum's Kitchen table)
Align a flat head screwdriver directly over the first pin position on the cassette, perpendicular to the 36T sprocket face and strike the top of the screwdriver with a hammer. Do not try to fully assemble the first pressfit with the first strike. Move around the cassette clockwise tapping each of the 18 pins into the X-COG. You should aim to fully assemble the press fit after repeating this procedure 3 times (Slide 13). At this point all of the standoffs should now be flush with the X-COG ring (Slide 15).
Congratulations you have now assembled your X-Cog 44T sprocket (Slide 16)
TUNING YOUR 44T
Chain length - standard procedure, wrap around big/big not through RD and add 4 links.
Adjust low limit screw - This will need to be readjusted as the big ring is now slightly offset from where the stock 42T was originally. The chainline of the 44T was adjusted to improve shifting into the larger sprocket.
B-screw - The b-screw tension will need to be increased. Start by adjusting the screw until there is no longer any whirring noise heard when shifting up from the 36T to 44T then add 1 full turn of the b-screw to prevent cage jamming when shifting up from smaller gears.