All engines covered in this guide are equipped with hydraulic valve lifters. Engines so equipped operate with zero clearance in the valve train; because of this the rocker arms are non-adjustable. The hydraulic lifters themselves do not require any adjustment as part of the normal tune-up, although they occasionally become noisy (especially on high-mileage engines) and need to be replaced. In the event of cylinder head removal or any operation that requires disturbing or removing the rocker arms, the rocker arms have to be adjusted. Please refer to . Hydraulic lifter service is also covered in .