While driving my 2001 Disco II, hit a pothole and started to hear a loud engine rattle that as soon as I pulled over it quieted down but was still there. Opened up the hood and the bolt on the front of the air compressor pulley was gone and although the pulley was still there, the splined cover (?) was laying on top of the cooling fan and had managed to chip the blades on the fan.
I got home, found a bolt that matched the threads on the splined shaft and attached the cover back onto the compressor.
When the compressor switch is on or off, the cover (?) still turns, the only difference I notice is of course the engine sound changes (under load, yes?). Every vehicle with AC I've owned, I notice that there is an electric clutch and it only starts spinning when the AC is turned on.
Is it supposed to be a special bolt? Am I missing a piece? Or is this normal operation?
Any info appreciated!

Edit: So an online search is telling me there's supposed to be shims (2.54mm) inside the clutch hub.

Fixed: found a 2mm washer that fit inside the hub and now it spins and stops spinning when AC turned on

 

Ok under the hub that fell off, where the spline shaft goes into. There are is a small stack of 2-3 washers (shims) this is how the air gap of the clutch is set. if they are not there and you put a bolt in the compressor is locked solid and will turn all the time and will not disengage. Remove the bolt and pull the hub, go to a hardware and find a few thin washers the will fit the hub and still allow the bolt to fit through. Add or remove washers until you get .025-.035 gap between the clutch and the hub

If you get it close it should work. Then remove the bolt and put a few drops of loctite on it to keep it from doing this again