it would be in the factory service manual but typically no one uses a torque wrench on valve covers. I would describe the amount of force to use, unless you are really strong, is the amount generated by using your wrist with a 3/8" wratchet, you do not want the force to involve your lower or upper arm. A pure guess would be 25 ft/lbs or less. Snug but not tight enough that you bend the metal.