VVL Cam Follower – Car and truck engines

What Is VVL Cam Follower?

In the context of internal combustion engines, a cam follower, also known as a tappet or lifter, is a mechanical component positioned between the camshaft lobe and the valve stem (or rocker arm) to translate the camshaft’s rotational motion into the linear reciprocating motion required to open and close the engine valves. A Variable Valve Lift (VVL) cam follower is a specialized evolution of this component, designed to facilitate dynamic changes in valve lift and duration, often in conjunction with Variable Valve Timing (VVT) systems. Its primary purpose is to provide an adaptable interface that allows the engine to switch between different cam profiles (e.g., low-lift/short-duration for fuel efficiency and smooth idle, high-lift/long-duration for increased power output at higher RPMs) on the fly, optimizing engine performance across the entire operating range. These followers are strategically located within the cylinder head, directly above or interacting with the camshaft, and form a critical part of the valvetrain assembly.

How It Works

The operation of a VVL cam follower is fundamentally based on the engagement of different cam profiles, often facilitated by a hydraulic locking mechanism. In many VVL systems, such as Honda’s VTEC or Nissan’s Neo VVL, a single valve (or pair of valves) is actuated by a rocker arm that can engage one of two or three distinct cam lobes on the camshaft: typically a low-lift/duration lobe for normal operation and a high-lift/duration lobe for performance. Here’s a step-by-step breakdown:

Default Operation (Low-Lift): At lower engine speeds and loads, the VVL system operates in its default, low-lift mode. In this state, two outer cam followers (integrated into the rocker arm assembly) ride on the low-lift/duration cam lobes, actuating the valves with minimal lift. A central, high-lift cam lobe spins freely above a separate central cam follower, which is not mechanically coupled to the valve actuation at this stage.
VVL Engagement Signal: When the Engine Control Module (ECM) determines that conditions are met for high-performance operation (e.g., specific RPM, load, engine temperature, throttle position), it sends an electrical signal to a VVL solenoid valve, typically located near the VVL rocker arm assembly.
Hydraulic Pressure Activation: The solenoid valve, upon activation, opens a passage, allowing pressurized engine oil to flow into a hydraulic chamber within the VVL rocker arm or cam follower assembly. This oil pressure acts upon a small piston or pin.
Locking Mechanism Actuation: The hydraulic pressure pushes a precision-fit locking pin (or set of pins) laterally. This pin slides into a bore, physically locking the three cam followers (two low-lift and one high-lift) or specific components of the rocker arm assembly together. Once locked, the entire assembly moves as a single, rigid unit.
High-Lift Operation: With the followers locked, the valve actuation is now dictated by the central, high-lift/duration cam lobe, which has a more aggressive profile. Because the outer followers are locked to the central one, they are effectively overridden, and the valve follows the motion profile of the high-lift lobe. This results in increased valve lift and duration, allowing for greater airflow into and out of the combustion chamber, boosting engine power.
Disengagement: When engine conditions no longer require high-lift operation, the ECM deactivates the solenoid. Oil pressure to the locking pin chamber is released, and a return spring within the mechanism retracts the pin, unlocking the followers. The system then reverts to low-lift operation, with the outer followers again dictating valve motion.

This dynamic engagement and disengagement are achieved with extreme precision, often within milliseconds, to ensure seamless transitions between performance characteristics.

Common Failures & Troubleshooting

Given their complex function and interaction with high-pressure oil and mechanical forces, VVL cam followers are susceptible to specific failures:

Symptoms of Failure:

Engine Misfires or Rough Running: Particularly noticeable during VVL engagement, as one or more cylinders may fail to switch profiles.
Reduced Power and Torque: If the VVL system fails to engage the high-lift cam profiles, the engine will lack its intended top-end performance. Conversely, if it gets stuck in the high-lift profile at low RPMs, it can cause rough idle and poor low-end torque due to excessive valve overlap.
Excessive Valvetrain Noise: Ticking, clattering, or rattling sounds emanating from the cylinder head, which can indicate worn surfaces, hydraulic lash adjuster (HLA) issues within the follower, or a sticking VVL locking pin.
Check Engine Light (CEL) Illumination: Accompanied by specific diagnostic trouble codes (DTCs) related to VVL system malfunctions (e.g., P1259, P2646, P1078, which may indicate VVL pressure switch, oil control valve, or system performance issues).
Increased Oil Consumption: While not a primary symptom, severe wear in the VVL mechanism can sometimes lead to oil starvation or oil leakage internally, contributing to increased consumption.

Wear Mechanisms:

Scoring and Pitting: The direct contact surfaces between the cam lobe and follower, or the roller bearing surface, can experience severe wear due to inadequate lubrication, high operational temperatures, contaminated oil, or prolonged stress.
Hydraulic Lash Adjuster (HLA) Failure: Many VVL followers integrate an HLA. These can fail due to sludge buildup, blocked oil passages, internal spring fatigue, or oil pressure issues, leading to improper valve clearance and noise.
VVL Locking Pin Sticking/Wear: The precision locking pin can become stuck due to sludge, debris in the oil, wear of the pin itself, or wear in its bore, preventing proper engagement or disengagement of the VVL mechanism.
Roller Bearing Collapse (for roller followers): If equipped with roller bearings, these can fail due to fatigue, contamination, or insufficient lubrication, leading to high friction and potential seizure.
Spring Fatigue: Internal springs within the follower or the locking mechanism can weaken, affecting proper operation of the HLA or the locking pin.

Diagnosis and Repair:

Diagnostic Trouble Code (DTC) Retrieval: Use a professional scan tool to check for VVL-related codes. These codes provide a starting point for pinpointing the system malfunction.
Oil Pressure Measurement: Verify that the engine oil pressure meets manufacturer specifications, particularly at the VVL solenoid and actuator, as insufficient pressure will prevent proper VVL engagement.
VVL Solenoid Test: Test the VVL oil control solenoid valve (OCV) for electrical continuity and proper mechanical operation (opening/closing). Often, a clogged filter screen on the OCV can cause issues.
Visual Inspection (with valve cover removed): Carefully inspect the VVL cam followers and corresponding cam lobes for visible signs of wear, scoring, pitting, or discoloration. Check for any obvious obstructions or loose components within the rocker arm assembly.
Stethoscope Diagnosis: Use an automotive stethoscope to pinpoint the source of valvetrain noise, differentiating between a general clatter and a specific follower or HLA issue.
Functional Test with Scan Tool: Some advanced scan tools allow for activation of the VVL system (or OCV) at idle, which can help in diagnosing whether the mechanism is responding. Monitor real-time data for VVL-related parameters.
Disassembly and Measurement: For definitive diagnosis, the valve cover and potentially the camshaft may need to be removed. Inspect the locking pins for free movement, check clearances, and look for wear on internal components of the follower or rocker arm.

Repair/Replacement: Repair often involves replacing the faulty VVL cam follower or the entire rocker arm assembly, as these are typically integrated units. If cam lobes are significantly worn due to follower failure, the camshaft may also require replacement. It is crucial to address the root cause, which often includes ensuring proper engine oil quality and adequate lubrication, and thoroughly cleaning or flushing oil passages to prevent recurrence of sludge-related issues.