1. Remove the Nexus shift mechanism by loosening the 10mm nut (can also be a 5mm allen wrench).
The unit pulls off the axle nut towards the right.
Set aside the shift pin that sits inside the hollow axle.
2. Loosen the axle nuts (15mm) on the internal gear hub, both left and right. Loosen the axle carrier lock down bolts (16mm for bolt and 17mm for nut). It helps to have a narrow, compact wrench like a open ended/box wrench to access the bolt head on the inside between the disc rotor and the frame.
3. Pull the internal geared hub backwards in the slotted dropouts of the frame until the tension on the primary chain is tight. Lock down the drive side (right side when upright) axle nut first. Lock down the non drive side (left) axle nut of the internal geared hub. Check primary chain tension by rotating the chain to see if there are any spots that are too tight.
4. Tension the secondary chain by pulling the whole axle carrier backwards. Lock down one bolt and check chain tension by rotating the left wheel in order to check for tight spots. Due to the many connection points there is a chance that there will be a tight spot and a loose spot of the secondary chain. This will remedy itself during the break in period. Use the tightest point in the secondary chain as the base line for this tension adjustment, meaning the chain should not be overly tight in this position.
5. Lock down all the hardware. Reinstall the shifting mechanism in reverse order of removal. On the Sturmey archer hub, the cable/shift chain should have no slack, but not be tight, when in gear 3. On the Nexus, make sure the shift pin is put in the hollow axle before reinstalling the shift mechanism.