When turning off the engine on my 1999 Land Rover Discovery TD5, I noticed that there was a metallic knocking sound just as the engine stopped.  With the bonnet lifted I listened for the sound while the engine was started and stopped.  The tapping sound was coming from the bottom of the front of the engine.  Further investigation identified the bottom pulley being faulty.

In this video, a tapping sound can be heard coming from the bottom pulley while the engine is running.  As the engine stops, a loud knocking can be heard.  While watching the video, I also noticed that the tensioner pulley is also moving while the engine is running.

After purchasing the new harmonic damper, I made a tool to stop the the pulley rotating while the centre bolt was loosened.

Removing the thermo-viscous fan

Removing the damping weight from the front of the old pulley

The damping weight removed from the front of the old pulley.

Using a ratchet wrench to move the tensioner away from the belt to allow the belt to be removed.

Loosening the centre crankshaft bolt after fastening the DIY locking tool to the front of the old pulley

The centre bolt is too long to remove while the radiator is in place, so the pulley is removed with the bolt loose but still in place.

A mark can be seen in this photo where the two parts of the damper have been hitting each other.

The end of the crankshaft after removing the pulley.

The old and new pulleys.

The new pulley located on the crankshaft.

The crankshaft bolt being tightened.  The original damper weight was then re-fitted.

With the new pulley fitted, the tapping noise has gone.