Crankshaft pulley.

[Carolyn]

I've had an annoying 'knock' coming from the belt area of the engine. I couldn't pin it down, even with my stethoscope.
 
So, yesterday I decided to watch all the pulleys carfully.  The crankshaft pulley was wobbling like mad.  I KNEW it wasn't loose.

I had a couple of spares,so I examined them.  They have a rubber damping membrane bonded into them.  So I reckoned that, perhaps that bonding was giving up the ghost.

Luckily, having a lift, it was a ten minute job to get the pulley off. At this point it should probably now be referred to as a harmonic damper. Sure enough part of the rubber was protruding from the surface.

In went the better of my spares and, hey presto!  No wobble and the knock is gone.

You can just see the rubber sticking out:
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A bit fuzzy, but you can see the rubber doesn't show.
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[thetyrant]

Well spotted .. its a common issue on other cars ive had especially the Evos which run same rubberised harmonic damper, i spotted mine wobbling just after a cold start one day when looking for rubbing noise i had been getting, was lucky i did as it was just before a 1500 mile euro road trip so was able to swap it in time, a friend wasnt so lucky with his when we were on track at Pembrey and his outer ring came right off at 8000rpm and flew down track in front of him!  photographer got a pic i will see if i can find it, lucky photo indeed to catch that

[Petrus]

same rubberised harmonic balancer

Carolyn correctly used ´damper´.

The bálancing ´equivalent´ is a dynamic balancer.

The role of the harmonic damper is to dampen harmonic frequencies in the crankshaft. Especially in cast crankshafts there are small flexes which at some frequencies can grow in amplitude because of interferencia. The harmonic damper ´absorbs´ that.
A well known example of prinicple is the rubber mounted weights at the end of motorcycle handlebars.

[thetyrant]

Ive corrected it to damper my apologies

[McMr2]

Are these pulleys common to all 1zz engines (i.e. readily available?)

[Carolyn]

Are these pulleys common to all 1zz engines (i.e. readily available?)

Yes.