If you have a vehicle that comes to your shop with valvetrain noise at start up, the solution might be simpler than you think. Many engines have variable valve timing, these systems need to have engine oil to operate. If the oil drains from the top end of the engine, the actuators and lifters will make noise when the engine is started. The cause could be a damaged oil drain back valve in the oil filter. Sponsored by NAPA.
Video courtesy Underhood Service.