All engines covered in this manual are equipped with hydraulic valve lifters. Engines so equipped operate with zero clearance in the valve train which is maintained by the lifters themselves. Therefore, the hydraulic lifters 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 must be adjusted so the lifters may perform their job of maintaining zero lash. Please refer to Engine & Engine Overhaul for these procedures.