Hydraulic valve lifters, also known as hydraulic lash adjusters, utilize pressurized oil to maintain zero valve lash in an internal combustion engine, ensuring quiet and efficient operation. Here's a breakdown of their function:
1. Lifter Components:
- Lifter Body: The main housing of the lifter, containing the internal components.
- Plunger: A piston that moves within the lifter body.
- Check Valve: A small valve (usually a ball or disc) that allows oil to flow into the pressure chamber but prevents it from flowing back out.
- Pushrod Seat: The top of the plunger where the pushrod (connecting to the rocker arm) sits.
- Oil Gallery: Passageways within the engine block that supply pressurized oil to the lifters.
- Metering Disc (Sometimes): Controls oil flow to the top of the engine.
2. The Process:
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Oil Supply: Pressurized engine oil is supplied to the lifter through an oil gallery in the engine block. This oil enters the lifter body.
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Filling the Chamber: The oil flows through a small orifice or check valve into the internal cylinder, filling the space beneath the plunger. The check valve prevents oil from flowing back out, maintaining pressure.
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Camshaft Lobe Contact: As the camshaft rotates, its lobe comes into contact with the lifter's bottom surface.
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Lifting the Valve: When the cam lobe pushes upward, the plunger, filled with pressurized oil, acts as a solid link, transferring the motion through the pushrod and rocker arm to open the engine valve. Because the oil is incompressible, the lifter effectively becomes a fixed length.
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Lash Adjustment: The hydraulic action of the lifter automatically compensates for any thermal expansion or wear in the valve train. As the engine heats up, parts expand. The oil pressure within the lifter slightly adjusts the plunger's position to maintain zero valve lash. Similarly, if any wear occurs, the lifter compensates by filling the resulting gap with oil, again maintaining proper valve train geometry.
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Bleeding Down (Minimal): When the valve is fully open, a small amount of oil may leak past the plunger, preventing the lifter from "pumping up" and holding the valve open. This is a normal and necessary function.
3. Advantages of Hydraulic Lifters:
- Reduced Valve Train Noise: By maintaining zero lash, hydraulic lifters eliminate the clicking or tapping sound associated with mechanical (solid) lifters.
- Automatic Lash Adjustment: They eliminate the need for manual valve lash adjustments, reducing maintenance requirements.
- Improved Engine Performance: Consistent valve timing and lift improve engine efficiency and power output.
4. Potential Issues:
- Lifter Collapse: If oil pressure is low or the lifter is worn, it may not maintain adequate pressure, resulting in a "collapsed" lifter and noisy operation.
- Air Entrapment: Air bubbles in the oil can cause lifters to lose their hydraulic function.
- Contamination: Dirty oil can clog the small orifices within the lifter, impairing its operation.
In summary, hydraulic valve lifters use pressurized engine oil to automatically maintain zero valve lash, resulting in quieter engine operation, reduced maintenance, and improved performance.
