Abstract: In a pneumatically operable clutch driven piston and cylinder compressor assembly a multiplate friction clutch comprises a drive member of the clutch carried on an input shaft which has internal bearings supporting the driven end of the compressor crankshaft and the drive shaft being rotatable in an island portion of the crankcase which carries a fluid pressure operable annular piston engageable with a shell of the clutch for release thereof, the arrangement permitting the clutch to be located at least in part within a projection of the cylinder of the compressor. A plurality of webs connecting the island portion with the crankcase are arranged to allow unrestricted communication between the compressor crankcase and a crankcase of an engine to which the compressor is mounted.