Abstract: An engine compression brake includes a link piston slidably mounted in a fuel injector or other rocker arm that can extend to cause it's rocker arm motion to be imparted to an associated exhaust rocker arm for achieving a compression brake action. In the retracted position the piston disengages from the exhaust rocker arm so that the engine runs in normal fashion. The piston is supplied with pressurized oil from a pre-existing lubricant line by a three way solenoid valve. This valve diverts oil from the line into a control passage in the rocker shaft that supplies one or more a injector or other rocker arms. The control passage supplies a system of passages, a check valve, and a vent valve in each arm. This valve and passage system supplies oil such that the link piston is extended or retracted. There may also be variable area orifice in the link cylinder to control force build-up, depending in the driving cam characteristics.