ASE A1 Engine RepairCylinder Head and Valve TrainMedium
A technician is performing a valve adjustment on an overhead valve (OHV) engine equipped with hydraulic lifters. The service information specifies 'zero lash plus 1/2 turn' for the rocker arm adjusting nuts. After achieving zero lash, the technician tightens the adjusting nut an additional 1/2 turn. What is the purpose of this additional 1/2 turn?
- ATo ensure the hydraulic lifter is properly preloaded.
- BTo compress the valve spring slightly for better sealing.
- CTo compensate for camshaft wear and maintain valve lift.
- DTo create a small amount of valve clearance for expansion.
Show answer & explanationAnswer & explanation
Correct answer: A. To ensure the hydraulic lifter is properly preloaded.
The additional 1/2 turn (or specified amount) after achieving zero lash on a hydraulic lifter system is to preload the hydraulic lifter. This ensures the lifter's internal plunger is depressed slightly, allowing it to function correctly in taking up valve train slack.
Why the other options are wrong
- B. While it slightly compresses the valve spring, the primary purpose is not for better sealing but for lifter preload.
- C. This adjustment is not designed to compensate for camshaft wear, which typically requires camshaft replacement.
- D. This procedure is for hydraulic lifters, which are designed to maintain zero lash. Creating clearance would defeat their purpose and cause noise.
Hydraulic Lifter Preload
The process of adjusting a hydraulic lifter to a specific depth (often 'zero lash plus X turns') to ensure proper function and prevent valve train noise.
- Required for proper hydraulic lifter operation.
- Eliminates valve train slack.
- Prevents ticking noises.
- Specific adjustment (e.g., 1/2 turn) varies by manufacturer.
Memory trick: Zero plus a turn, for the lifter to learn.