In an exhaust valve mechanism for an internal combustion engine the main rocker arm is mounted on a rocker arm shaft for normal valve operation via a cam element. A secondary rocker arm is mounted on the shaft for activation of an exhaust brake mode. The activation is achieved through supply of hydraulic pressure to a piston cylinder arrangement acting between the main and secondary rocker arms. A master piston and a slave piston are connected by a hydraulic-link allowing activation by increased hydraulic pressure. When activating the exhaust gas temperature increasing mode, the master piston is moved to an active position for part of its stroke against the force of a first resilient member. When activating the exhaust brake mode, the master piston is moved the full movement of its stroke against the combined forces of the first resilient member and a second resilient member as active position. The end of the first stroke length defines a position for the master piston allowing activation of an extra valve event.