ASE A1 Engine RepairCylinder Head and Valve TrainEasy
A technician is performing a valve adjustment on an overhead valve (OHV) engine with hydraulic lifters. The engine has been run to operating temperature. After backing off the rocker arm nut, the technician slowly tightens it while rotating the pushrod until resistance is felt. From this 'zero lash' point, the technician then tightens the nut an additional 1/2 turn. What is the primary purpose of this additional 1/2 turn?
- ATo ensure the rocker arm stud is fully seated in the cylinder head.
- BTo compress the valve spring to its specified installed height.
- CTo properly preload the hydraulic lifter plunger.
- DTo compensate for thermal expansion of valve train components.
Show answer & explanationAnswer & explanation
Correct answer: C. To properly preload the hydraulic lifter plunger.
The additional 1/2 turn past zero lash on a hydraulic lifter system is specifically to create the correct preload on the lifter’s internal plunger, allowing it to function correctly and take up slack in the valve train.
Why the other options are wrong
- A. The rocker arm stud seating is typically achieved during initial assembly and torquing, not during valve adjustment.
- B. Valve spring installed height is set by shims or valve job procedures, not rocker arm adjustment.
- D. While it compensates for some expansion, the primary goal is hydraulic lifter preload, which inherently handles minor expansion.
Hydraulic Lifter Preload
The precise amount a hydraulic lifter's internal plunger is compressed from its fully extended position at zero valve lash, ensuring it can effectively take up slack in the valve train and maintain quiet operation.
- Prevents valve train noise by eliminating lash.
- Allows for thermal expansion and component wear.
- Too much or too little preload causes problems.
Memory trick: Preload is key for lifter's quiet, smooth play.