Types of Engine Liftersby Tony Oldhand
An internal combustion engine has hundreds of components. One of the critical components is the lifters, also called tappets. Lifters ride on the camshaft and lift the push rods. The push rod, in turn, pushes on one side of a rocker arm, like a teeter-totter. The other side of the rocker arm pushes down on the valve when the camshaft pushes up on the lifter. There are three types of lifters used in engines, and all three have their pros and cons.
Solid lifters are made of a solid rod of hardened steel. Most are about 1 inch in diameter and 2 inches in length. The bottom of the lifter rides on the camshaft, and the top has a small depression where the push rod sits. According to Ball State University, solid lifters were commonplace in the 1960s and the 1970s. The advantage to a solid lifter is that it does not lose horsepower in the process of lifting. The drawback is that the rocker arm can go out of adjustment quite often. If you hear a car engine make a clack-clack-clack-clack sound when going down the road, it's because the rocker arms are out of adjustment and hammering the valves. Currently, solid lifters are used in racing engines due to the horsepower loss factor of hydraulics.
A hydraulic lifter looks very similar to a solid lifter, except for one important internal difference: It is designed to be a self-adjusting shock absorber, using engine oil as the working fluid. When the camshaft lobe pushes up on the bottom of the lifter, an internal pool of oil pushes up on a piston and spring assembly. The internal piston pushes on the push rod. Due to this process, no rocker arm adjustment is needed since the lifter self-adjusts the entire valve train. The upside to hydraulic lifters is that the initial shock of contact is taken up by the oil, eliminating the constant need for rocker arm adjustment. The downside is that because it absorbs shock, the engine loses horsepower through the valve train. Moreover, hydraulic lifters have internal mechanical components that wear out, causing oil bypass or bleed-down. When it does wear out, the lifter no longer lifts. This condition is known as a "collapsed lifter."
Roller lifters are a significant advancement in automotive engine technology. Whereas a conventional lifter is cylindrical, with a flat bottom that rides on the cam lobe, a roller lifter uses a small wheel at the bottom, so the wheel rides on the cam lobe. This reduces friction significantly since the lobe does not scrape but rather rolls on the lifter. Roller lifters are available as solid lifters, for racing applications, or hydraulic, for conventional applications. The advantage of roller lifters is reduced friction at the cam. The drawback is increased cost since more manufacturing steps are involved in their production.
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