Top mount trouble Help pls!!!

[maddog]

Brought some Fk coil overs second hand, I've fitted rears but had to take fronts to a garage to get my standard top mounts fitted because I don't have any spring compressors... when the guy swapped one over he tightened it up but when he rotated the top mount with his hand the centre nut started undoing itself as if the bearing wasn't doing its job.

He took it apart twice but couldn't fathom it he said maybe theres some sort of washer missing?
As it stands each front coilover has the springs then on top there's a big flat metal disk and the bearing is in the top of that,
Does anyone know anything I might be missing or a guide with pictures would be much appreciated... Thanks a lot Dan