The valve lifter follows the camshaft lobe in an engine and opens and closes the valves. The valve lifter, or lifter as it is commonly referred to, comes in many different styles. Each style represents the type of camshaft that the lifter rides upon. There are hydraulic lifters in both flat tappet and roller types, as well as solid or mechanical lifters in flat tappet and roller types as well.
Each type of valve lifter has its own positive and negative characteristics. The hydraulic flat lifter is the least expensive to purchase and perhaps the most common style of valve lifter used. It rides on the camshaft's lobes and uses oil pressure to apply a slight pre-load to the push rod. The positive aspect of this lifter is its ease of maintenance and use. The disadvantage of this style of lifter is its ability to pump up or float the valve at high engine RPM, or revolutions per minute.
The solid valve lifter in flat tappet form also rides on the camshaft lobe. This lifter, however, uses a pre-determined clearance setting to operate the valve. The clearance is dictated by the camshaft manufacturer and is set at the rocker arm/push rod seat. The advantage of this lifter is its cost and ability to set lifter clearance to RPM. The disadvantage of this lifter is that it is noisy and needs continual adjustment to ensure proper operation.
Flat tappet camshafts and valve lifter assemblies produce friction and horsepower-robbing drag. They are often subjected to wear and will sometimes cause erratic valve timing due to extreme wear. The cure for this power-robbing system comes in the form of a roller camshaft and a roller valve lifter.
The roller valve lifter incorporates a steel wheel at the base of the valve lifter. This wheel rides along on the camshaft's lobe. This design prevents friction and increases horsepower. It also prevents premature wear. The roller style lifter comes in both solid or mechanical and hydraulic designs. This type of lifter requires a stronger valve spring to ensure that the roller remains in contact with the camshaft lobe at high engine RPM.
The benefit of a roller system is the increase in horsepower and fuel savings potential over that of a flat tappet system. The negative aspect of the roller system lies in the high cost. Also costly are the increased pressure valve springs that are needed to keep the lifters positioned on the camshaft lobes.