The adjustors are employed to keep the correct amount of tension on the timing chains and accoring to the Fiat documentation the tension should be checked every 10,000km. There are 2 adjustors per engine (one for each cylinder bank) and their design changed 3 times over the different 2.0 litre and 2.4 litre engines as we shall see.
This type of adjustor was fitted to the earliest 2.0 litre engines and relied on manual measuring of the chain movement at specific point and with a specific perpendicular tension applied. Once the adjustor had been positioned correctly within the allowed tollerences, a side screw is tightened to fix that position.
There was a major redesign of the mechanism mid-way through the 2.0 litre engine production whereby a spring system was employed thus doing away with the manual chain deflection measurment and side locking screw. Adjustment is much easier with this system as the end locking cap just needs to be undone and the engine manually turned over a few times for the tension to be automatically regulated. It must be said that it is advisable to also manually check the chain deflection "just in case".
The 2.4 litre engine had basically the same system as the later 2.0 litre engines with just the internal spring different.
Later End Caps
A final modification was to the end caps where an aditional locking screw was fitted to ensure there was no movement of the cap.