Hi all, just replaced my alternator pulley and new belt but on way home noticed a loud knocking from the belt area that comes and goes. Tensioner felt ok when putting the belt on could this be the fault amplified by a new pulley and belt?

Take the belt back off and try it

Replaced tensioner tonight, tried it with the belt off and no noise, think it's the air con compressor, sounds like a real violent knock and its constant now, no play in air con pulley but you can just spin it freely and it clicks a bit and spinning the pulley back and forth gets a noise too.

The air con pulley has an electromagnetic clutch, which only works with engine running. With the engine off only the outer piece will move. You need to check both the inner and outer parts rotate with the air con on and the engine running.

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Agh, with the engine off the inner is spinning freely, engine running and air con on the outer pulley turns only. What would cause the loud knocking, internal damaged?

Agh, with the engine off the inner is spinning freely, engine running and air con on the outer pulley turns only. What would cause the loud knocking, internal damaged?

Yep fairly common problem. Check the wires to the clutch and also check the inner part of the pulley stays still with the shaft. The but can come loose and strips the splines off the shaft. Alternatively if there is no gas in the system it won't engage the clutch.

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Yep fairly common problem. Check the wires to the clutch and also check the inner part of the pulley stays still with the shaft. The but can come loose and strips the splines off the shaft. Alternatively if there is no gas in the system it won't engage the clutch.

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Cheers, replacment on order!

So replaced the full air con compressor this afternoon and fired her up, noise still exactly the same ( knocking like a cement mixer now haha) so popped to euros and picked up a new alternator and that sorted it!

So wasted my money on the original alternator pulley, belt, tensioner and air con compressor ( should of just changed the bloody alternator 1st!!) oh well at least that lot should be trouble free for a while!!

at least you have some spare parts now ;-)