What Are the Egg-Shaped Pieces on a Camshaft Called?
They are called cam lobes. These egg-shaped protrusions on a camshaft control when and how far engine valves open and close, orchestrating the timing that lets an engine breathe efficiently and make power. Understanding cam lobes helps explain everything from idle smoothness to high-RPM performance in modern and classic engines alike.
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Definition and Terminology
A camshaft is a rotating shaft fitted with multiple cam lobes. Each lobe—shaped eccentrically like an “egg”—translates the rotational motion of the shaft into linear movement of valve train components. In most engines, each cylinder has at least two lobes: one for the intake valve and one for the exhaust valve. On some older engines, extra lobes may also drive a mechanical fuel pump or a distributor.
Intake vs. Exhaust Lobes
Intake lobes open the intake valves to let the air-fuel mixture in; exhaust lobes open the exhaust valves to expel combustion gases. Their shapes and timing can differ to match airflow requirements and emissions targets, contributing to an engine’s performance character and efficiency.
How Cam Lobes Work
As the camshaft rotates, each lobe’s changing radius lifts a follower (tappet, lifter, or rocker) off its base circle, opening a valve against spring pressure. The lobe’s precise geometry determines lift (how far the valve opens), duration (how long it stays open), and the specific opening/closing rates that affect idle quality, torque curve, and emissions.
The following list identifies the principal parts of a cam lobe and their roles in valve motion:
- Base circle: The round “resting” portion where the valve remains closed.
- Opening/closing ramps: Gentle transitions that start and finish valve movement to reduce shock and wear.
- Flanks: The steeper sections that accelerate valve lift and control airflow onset.
- Nose (or peak): The highest point of the lobe, delivering maximum valve lift.
Together, these features shape how smoothly and aggressively a valve is actuated, balancing performance, durability, and noise.
Engine builders describe cam lobes using several key specifications that quantify their behavior:
- Lift: Maximum valve opening height, often listed as valve lift (after rocker ratio) and lobe lift (at the cam).
- Duration: How long the valve is open, measured in crankshaft degrees at specified lift thresholds (e.g., 0.050 in/1 mm).
- Lobe separation angle (LSA): The angle between the intake and exhaust lobe centers on the same cylinder, influencing overlap and idle quality.
- Advance/retard (phasing): The installed position of the cam relative to the crank, shifting torque toward low or high RPM.
These parameters interact: more lift and duration can boost high-RPM power, while wider LSA and conservative ramps tend to support smoother idle and better emissions.
Variations and Modern Technologies
Cam lobe design has evolved alongside emissions rules and performance demands. Today’s engines often use advanced materials, coatings, and variable systems to extract more efficiency without sacrificing drivability.
Flat-Tappet vs. Roller Profiles
Flat-tappet cams use a flat follower that rides on the lobe, while roller cams use a small wheel. Roller profiles allow more aggressive lobes with reduced friction and wear, supporting higher lifts and RPM with improved durability.
Variable Valve Timing (VVT) and Cam Phasing
Many modern engines feature hydraulically actuated cam phasers that advance or retard the camshaft relative to the crank. This shifts the effective timing of the lobes on the fly, optimizing torque, fuel economy, and emissions across the rev range.
Variable Lift and Cam Profile Switching
Systems such as Honda VTEC, BMW Double VANOS with Valvetronic, Toyota VVTL-i, and others may switch between multiple lobe profiles or vary effective lift and duration. Some approaches blend mechanical and electronic control to tailor valve events to load and speed, improving both low-end drivability and top-end power.
Common Misconceptions
In casual conversation, people sometimes call the entire protrusion a “cam,” but technically, the shaft is the camshaft and each egg-shaped projection is a cam lobe. On multi-cylinder engines, there are many lobes—typically one per valve—precisely aligned and indexed to the crankshaft via a timing belt, chain, or gears.
Summary
The egg-shaped pieces on a camshaft are cam lobes. Their geometry dictates how and when valves open and close, governing an engine’s breathing, torque curve, and efficiency. With modern advances such as roller followers, cam phasing, and variable lift, cam lobes remain central to engine performance—from smooth idle to high-RPM power.
What are the bumps on a camshaft called?
A camshaft is a long piece of metal that helps the engine work, kind of like breathing. It has special bumps, called lobes, that open and close little doors called valves.
What are egg-shaped protrusions machined onto a camshaft?
The egg-shaped protrusions on the cam (bottom) are known as lobes. Lifters ride on the rotating lobes and actuate the valves through the pushrods and rocker arms (top). As the lobe rotates to its smallest side, the springs close the valves.
What is the egg-shaped part of the camshaft called?
A camshaft is a long bar with egg-shaped eccentric lobes (cam lobes), one lobe for each valve and fuel injector (if engine does not have a common rail fuel injection system). Each lobe has a follower. As the camshaft is rotated, the follower is forced up and down as it follows the profile of the cam lobe.
What are the things called on a camshaft?
The camshaft consists of a cylindrical rod running the length of the cylinder bank with a number of cams (discs with protruding cam lobes) along its length, one for each valve. As the cam rotates, the lobe presses on the valve (or an intermediate mechanism), thus pushing it open.
