Cm870 compressor

[Signature620]

You can try removing it and timing it to the engine.

Turn the engine over until the "insert pin" mark on the damper lines up with the mark on the lower gear cover.
Remove the compressor and rotate the gear so that the X lines up with the cutout in the housing (3 o'clock position looking from the front). Refit the compressor and see if it's any better.

If it still knocks excessively it might be getting tired in the bottom end. Keep in mind that they usually make a noticeable knock - It might be OK.