The Little Rollers That Changed Engines Forever

The design and construction of the engines that power automobiles have evolved by both evolution and revolution over the nearly 140 years since Karl Benz’s Patent-Motorwagen chuffed about the countryside. Benz’s single-cylinder required numerous steps just to start. It could only run for so long before requiring at least some amount of fiddling. In comparison, modern engines are comically complex in their operation but wildly simple to maintain. What changed?

Well, lots of things. Material science has progressed leaps and bounds in the last 100+ years, but all the formulations of steel and aluminum in the world would be useless without precise control of an engine’s internal systems. That’s why so many revolutions in engine design centered on the orientation and actuation of the intake and exhaust valves—together known as the valvetrain. However, the key to a reliable and dependable modern valvetrain boils down to a simple roller.

The roller in question sits at the tip of the lifter, a key piece that translates the rotational motion of the camshaft into the linear motion of the pushrod, which acts on the rocker arm to open the valve. Spring pressure keeps the valves closed and, as engines have adopted higher and higher redlines, spring pressures have increased to better control the valves and ensure proper cycling of fuel and air. (Yes, I know desmodromic valvetrains exist, but they are relatively uncommon compared to traditional spring closures.)

That additional spring pressure has turned out to be the root of some interesting automotive developments. As these spring pressures were increasing, governments began to mandate emissions equipment. The addition of catalytic converters, and other tailpipe-emissions monitors and cleanup efforts, conspired to take certain additives out of regular engine oils. The main additives that got removed belonged to a family of compounds (zinc dialkyldithiophosphates, or ZDDP) that are critical to cushioning the connection between the lifter and the camshaft. Jason Fenske of Engineering Explained recently covered the topic in-depth, and his YouTube video is worth watching:

Lifters have a slight dish on the face that rides on the cam, but to the naked eye they look flat—hence the name. Without proper lubrication between the cam and lifter, those flat tappet lifters would either be eaten away by the cam, or the lifter would wear away the camshaft. Either way, not good.

While ZDDP was common in oils, flat-tappet lifters worked great for decades, but when those zinc compounds were removed, and as spring pressure increased and camshaft profiles grew more aggressive, damage to the lifter or camshaft became significantly more common. Replacing the flat tappet lifter with one that incorporated a roller that rode on the camshaft solved many problems and eliminated the need to change your oil formula.

These simple rollers changed the game and even opened the door to more performance. Since the reduction in friction lowered the risk of wiping material from the lifter or camshaft, the profile of the camshaft lobe could be altered in ways previously unimaginable. Higher lift with a more aggressive ramp than ever was not an issue, since the roller rotated with the cam. No additives were needed, so the emissions systems functioned as intended and maintenance intervals could stretch ever so slightly.

Friction is the enemy of an engine. Friction takes horsepower and turns it into heat and destruction. Essentially we have found two ways to reduce friction in the valvetrain: Oil additives like ZDDP and lower-friction components like roller lifters and rocker arms. Luckily now we have access to parts that can retrofit vintage engine designs with roller valvetrains, and we can purchase specially formulated oils or additives that will keep our engines running for a long time—as long as we maintain our vehicles properly and choose the correct oils.