The original crankshaft pulley has a built in damper.

The damper is used to stop external vibrations from being transmitted to the crankshaft and eventually preventing catastrophic bearing damage.

Beware of any of the 'lightweight' pulleys as they are indeed lightweight, but they're also transmitting vibrations from the alternator or the camshafts straight into the crankshaft and vice versa. Light isn't always better..

This is an original equipment (Rover) pulley which is suitable for all 1.8 litre K-Series engines.