A camshaft phaser includes a rotor, a stator, a torsional rotor bias spring, and a spring retainer wherein the spring retainer is fixed to either the rotor or stator when the nominal spring preload is reached to retain the nominal spring preload in said phaser. In one embodiment, the rotor has a bore formed therein, and the spring retainer has an arcuate slot coincident with the rotor bore. The spring retainer is rotated past the rotor until a predetermined spring preload is achieved. A retaining feature is installed through the arcuate slot into the rotor bore, thereby biasing the rotor in the predetermined bias position at the predetermined bias spring preload. In another embodiment, the spring retainer is a rotatable cam feature that becomes fixed to the stator after spring adjustment is complete.