Modern internal-combustion engines are full of moving parts — pistons, camshafts, valves — and among the unsung heroes of the valve train are the humble tappets and rocker arms. Although small, these components play a critical role in translating the camshaft’s motion into the opening and closing of the intake and exhaust valves. In this article, we’ll break down what tappets and rocker arms are, how they work, why they matter — and what can go wrong if they’re not properly maintained.
What Is a Tappet?
A tappet (also called a valve lifter or cam follower) is a cylindrical mechanism that converts the rotational motion of the camshaft into a linear motion used to actuate engine valves.
| Feature | Description |
|---|---|
| Function | Transmit camshaft rotation into vertical motion to open/close valves |
| Location | Between camshaft and valve (or pushrod) depending on engine design |
| Common Types | – Solid (mechanical) tappets – Hydraulic tappets – Roller tappets (with rolling contact) |
| Adjustment | Solid tappets require manual valve-clearance adjustment; hydraulic tappets automatically compensate. |
Why the Type Matters
-
Solid (mechanical) tappets — simple and robust, but need periodic adjustment of valve clearance (“lash”) to keep engine running smoothly.
-
Hydraulic tappets — self-adjusting, ideal for quieter operation and reduced maintenance.
-
Roller tappets — use a rolling element to reduce friction and wear, often found in performance or high-RPM engines.
What Is a Rocker Arm?
A rocker arm is the lever that transmits motion from the tappet (via a pushrod in many engine designs) to the valve stem, causing the valves to open or close. In essence, it “rocks” — converting upward push into downward valve actuation (or vice versa).
Most rocker arms are made from stamped steel, though aluminum or forged steel may be used for lightweight or high-performance applications. Some advanced designs even feature roller-bearing contact surfaces — known as “roller rockers” — to reduce friction and allow higher RPM operation.
One key characteristic is the rocker ratio — the ratio between the movement at the pushrod/tappet side and at the valve side. Common rocker ratios are around 1.5–1.8:1. That means a small cam movement can produce a greater valve lift, enhancing airflow and performance.
How They Work Together: Valve Train Dynamics
Here is a simplified step-by-step flow of how tappets and rocker arms interact within a valve train (especially in a classic OHV/pushrod engine):
-
The camshaft lobe rotates as the engine runs.
-
The cam pushes on the tappet (valve lifter), causing it to move upward (or downward depending on design).
-
The tappet motion is transferred to a pushrod (in pushrod engines).
-
The pushrod pushes on one end of the rocker arm.
-
The rocker arm pivots on its fulcrum, transmitting force to the valve stem, pushing the valve open.
-
Springs return the valve (and rocker arm/pushrod/tappet) to the closed (rest) position, ready for the next cycle.
In engine types with overhead camshafts (OHC/DOHC), tappets may act directly on the valve stem or via “bucket tappets,” sometimes without rocker arms at all.
Why Tappets & Rocker Arms Are Vital
-
Precise Valve Timing & Lift — correct valve actuation ensures proper intake of air-fuel mixture and exhaust of combustion gases, critical for engine performance and efficiency.
-
Durability & Wear Resistance — tappets and rocker arms operate under continuous load and high speed; good design and lubrication reduce wear and extend engine life.
-
Noise Reduction — hydraulic tappets and roller-rocker setups reduce “tappet noise” (ticking, tapping) often heard on startup or under load.
-
Performance Potential — with the right rocker ratio and low-friction components (e.g., roller tappets/rockers), engines can achieve higher RPMs, better airflow, and increased power.
What Can Go Wrong — Common Problems & Symptoms
| Problem / Issue | Symptoms / Consequences |
|---|---|
| Worn tappets or rocker arms | Tapping or clicking noise, poor valve operation, rough idle, loss of power |
| Insufficient lubrication | Increased wear, overheating, scoring of cam lobes or tappet base, premature failure |
| Incorrect valve clearance (for solid tappets) | Valve leakage, loss of compression, misfires, noisy operation |
| Excessive friction / poor materials | Reduced performance, higher fuel consumption, reduced lifespan of valvetrain components |
Maintenance — especially ensuring proper valve lash (if mechanical), clean oil supply, and suitable lubrication — is key to avoiding these issues.
Types of Tappets & Rocker Arms — Overview
Tappet Types
-
Solid (mechanical) tappets — simple, reliable, but require manual adjustment of valve clearance.
-
Hydraulic tappets (lifters) — self-adjusting, smooth, quiet, and low-maintenance.
-
Roller tappets — with a rolling surface to reduce wear and friction, beneficial for performance engines.
Rocker Arm Types
-
Standard stamped-steel rocker arms — widely used in mass-produced engines, cost-effective.
-
Aluminum or forged rocker arms — lighter, reduce reciprocating mass, better for high-RPM engines.
-
Roller rocker arms — equipped with bearings to reduce friction between rocker and valve stem or cam, used for performance or long-life applications.
Getting Replacement Parts — When to Consider Upgrading / Replacing
If you notice persistent tappet noise, valves not seating properly, misfires, or a drop in performance, it might be time to check the tappets, rocker arms, and related valvetrain components. Replacing worn parts with quality components — especially roller tappets or alloy rocker arms — can restore engine smoothness, improve efficiency, and even boost performance.
If you need replacement parts, you can buy Rocker/Tappet online from a specialized supplier.
Conclusion
Although often overlooked, tappets and rocker arms are vital for the proper operation of your engine. They translate camshaft motion into precise valve action — in turn controlling airflow, combustion efficiency, power output, and overall engine health. Understanding their roles, the differences between tappet and rocker types, and the importance of maintenance can help you keep your engine running smoothly, avoid damage, and even improve performance. Whether you run a vintage OHV engine or a modern overhead-cam design, treating your valve train components with care will pay off in longevity and reliable performance.