Why do some engines use hydraulic lifters? – Jalopnik

The engines of old were quite simple, with valve tappets that clicked on the cam lobes, opened valves and made noise in the process. Mechanical valve tappets were sufficient for valve operation, but they required a small amount of backlash, or whiplash, that must be adjusted periodically. They are also noisier and wear out more over time. Hydraulic lifters, on the other hand, have solved some of these problems. They contain an internal piston and use engine oil to automatically maintain whip action, allowing them to operate quieter with less maintenance but rely on clean, good lubrication.

Hydraulic valve tappets first appeared in the 1930s, but didn’t really take off until Cadillac used them in its legendary V16. That engine proved to be an irresistible turning point, demonstrating that a valve lifter that by itself maintains zero valve clearance makes the engine smoother and much easier to live with. Soon, solid lifters began to be phased out, and there are only a few automakers still holding on to them.

When an engine gets hot, it causes the internal components to expand due to the heat. Some space is needed to accommodate this expansion. In engines with an overhead camshaft, this clearance is necessary between the tips of the rocker arms and the tops of the valve stems. That slack is called eyelash. But it has to be just right. Too narrow and the valve seat would be incorrect, causing compression problems and burned exhaust valves. Too wide, and you’re looking down the barrel of reduced engine performance and increased noise. Wear to the valve system means that this clearance must be constantly checked and adjusted for optimal performance.

Racing engines also rely on lash adjustments to fine-tune power. A tighter whip (or less clearance between components) increases lift and duration for high rpm. More whip reduces lift and improves low-end response. Hydraulic lifters avoid routine lash checks, but they still require adjustment first so that the plunger operates in the mid-range.

Despite the name, a hydraulic lifter is not a small oil pump. It looks more like a self-correcting spacer with an oil pressure piston in it. As the camshaft rotates, the rising and falling profile of each lobe pushes the lifter in a precise pattern timed to the cylinder, transmitting the motion through the pushrod to the rocker arm. When the lifter rides on the base circle of the cam, oil fills the internal cavity and raises the piston. As the lobe rises, a check valve catches the oil, making the lifter work solidly and allowing the valve to open. Once the lobe passes its peak, the pressure drops, the chamber refills with fresh oil and the cycle repeats smoothly and quietly.

If proper oil pressure (considered healthy) and clean lubrication are maintained, this constant cycle will ensure that whipping does not occur for the life of the engine. It’s just old-fashioned, clever engineering, but it frees us all from the hassle of constant manual adjustments.

To summarize, the singing tap or tapping sound, also called valve chatter, is common in mechanical valve systems. The culprit behind that sound is whiplash, the small space that temporarily closes when the cam gets play and the valve clicks open. Hydraulic valve adjusters eliminate this gap and maintain zero clearance at all operating temperatures. This reduces the hammering effect that occurs when closing valves repeatedly hits the valve line hardware at high rpm. Because the valves don’t have to fill an air gap, they can simply follow the cam lobe and close gently, resulting in quieter operation and extending the life of the rocker arm ends, valve stems, cam lobes and pushrods since they don’t wear as much.

For all their advantages, hydraulic lifters are not invincible. Oil contamination, low oil pressure, or aerated oil can cause a lifter to collapse, causing the lashes to grow larger and creating that classic tapping sound. Here’s how to keep them quiet if that ever happens. A faulty check valve in the lifter can also release pressure too quickly or not hold pressure at all. But thanks to clean, high-quality oil and regular maintenance intervals, hydraulic valve tappets are extremely durable.

Today, consumer expectations and emissions regulations have forced almost all modern production engines to use hydraulic valve lifters. In a world where buyers and regulators alike want peace and quiet while driving, hydraulic valve lifters are a no-brainer.