Knocking noise after replacing serpentine belt
 

As per the title. Belt replaced recently. Car left to idle this morning on start-up to clear frosted windows etc. Noticeable knocking sound from the front of the engine.

Picture of belt attached. I assume the item highlighted by the red arrow is a tensioner and is meant to flex to-and-fro. The knocking sound seemed to come lower down, maybe the blue arrow item? It didn't seem to be coming from the alternator.

The item arrowed (air-con compressor?) moves/rotates in small increments when the engine is running. The position of the three bolts can be seen moving. I guess that shouldn't be happening. This is while the air-con is "Off". I've not tried with the air-con "On". I've a short video but can't find how to upload any video attachments.

If I understand it correctly, that sounds like the pulley clutch is not fully disengaging. When the A/C is off (ECON) the driven part of the pulley with the 3 "lugs" on it, stays in one place on my car. No movement at all. Just to check for you, I put a dab of white paint on one of the lugs. After a 6 mile drive, on ECON setting, the "white" lug was still in the same place.

If the clutch is on the way out, best to get a new compressor with pulley/clutch generally, since separate pulley/clutch units are almost as expensive as the whole compressor with the pulley/clutch, if indeed you can find one.

Seems a replacement compressor from RockAuto is advisable. What's the considered advice regarding driving the car in the interim? If the heater control unit is "Off" presumably there's no load on the compressor other than not fully disengaging. When I ran it yesterday on "Demist" everything seemed to be whizzing around soundlessly. With the caveat that last Sunday there was the knocking sound from somewhere.

Provided that your air conditioning is charged with refrigerant gas you can continue to drive the car David.

Just a thought, does your V8 have an air conditioning relay in the underbonnet fusebox? If so, try substituting one of the same physical type and see if it makes any difference.

Simon

MG ZT260 / Rover 75 V8 A/C Revival Bundle Kit on its way from DMGRS. Hopefully the solution. Fitting the end of next week. Not far to travel to the garage, half-a-mile max. Should be ok?