Hi Bulent

The torque on the Compressor Nut for the S120 Kit is 18N-m.

I'm not sure which o-ring your talking about. The o-ring around the perimeter of the diffuser cover acts as a seal to the combustion chamber case. The o-ring in the shaft tunnel acts as a damper for the shaft and also allows the bearing to move with respect to the pre-load system. This o-ring must be installed for the engine to operate properly.

Sincerely,
Ed