A vane-type camshaft phaser for varying the timing of combustion valves in an internal combustion engine. The phaser includes a seat formed in the sprocket at the appropriate position of intermediate rotor rotation and a locking pin slidably disposed in a vane of the rotor for engaging the seat to lock the rotor to the stator at the intermediate position. A bias spring system disposed on a cover plate urges the rotor toward the intermediate locking position from any position retarded of the locking position but does not engage the rotor during valve timing-advance motion thereof from the intermediate locking position.