What Is A Gap Cam On A Car

The world of automotive technology is constantly evolving, bringing us innovations designed to enhance performance, safety, and even convenience. One such intriguing piece of technology, often discussed in the context of engine diagnostics and performance analysis, is the "gap cam." But what exactly is a gap cam, and what does it do?

Understanding the Gap: Valve Lash and its Significance

To understand the purpose of a gap cam, we first need to delve into the inner workings of an internal combustion engine, specifically focusing on the valve train. The valve train is the mechanical system responsible for opening and closing the intake and exhaust valves, allowing air and fuel into the cylinders and exhaust gases out. This intricate dance of precisely timed movements is crucial for efficient engine operation.

One critical aspect of valve train maintenance is ensuring the correct valve lash, also known as valve clearance. Valve lash refers to the small gap or clearance between the rocker arm (or other actuating mechanism) and the valve stem when the valve is fully closed. This gap is intentionally designed into the system to account for thermal expansion and manufacturing tolerances. As the engine heats up, components expand. Without valve lash, the expanding parts could prevent the valve from fully closing, leading to a loss of compression, burned valves, and significantly reduced engine performance.

Too little valve lash (a gap that is too small) can lead to the aforementioned valve closure issues. Too much valve lash (a gap that is too large) can result in noisy operation (often described as valve "ticking"), reduced valve lift (meaning the valve doesn't open as far as it should), and decreased engine power. Therefore, maintaining the correct valve lash is paramount for optimal engine performance and longevity.

Introducing the Gap Cam: A Precision Tool for Measurement

The gap cam, or valve lash adjustment tool as it is sometimes called, is a specialized tool designed for precisely measuring and adjusting valve lash. It's not a camera, despite its name implying a visual element. Instead, the name likely comes from its function: to accurately determine the size of the "gap." The tool itself is usually a calibrated dial indicator or a set of precision feeler gauges integrated into a dedicated mechanism.

Types of Gap Cams

Gap cams aren't a one-size-fits-all solution. They can vary in design and complexity, depending on the engine type and the specific valve train configuration.

Dial Indicator Type: This type of gap cam utilizes a dial indicator, a precision measuring instrument, to quantify the valve lash. The dial indicator is mounted on a fixture that allows it to be positioned accurately over the valve stem. A probe extends from the dial indicator and rests on the rocker arm (or other actuating component). By carefully manipulating the tool, the dial indicator measures the distance the rocker arm travels before contacting the valve stem. This distance represents the valve lash. The dial indicator provides a very precise reading, often to the nearest thousandth of an inch.
Feeler Gauge Integrated Type: While not a 'true' gap cam in the same sense as the dial indicator type, some specialized tools integrate feeler gauges into a mechanism that aids in more precise and repeatable measurements. These tools often feature a handle and a dedicated tip that is inserted between the rocker arm and the valve stem. A set screw or locking mechanism then allows the feeler gauge to be held securely while the adjustment is made. This prevents the gauge from shifting during the adjustment process, improving accuracy.
Specialized Engine-Specific Tools: Certain engine manufacturers may develop specialized gap cams tailored to specific engine models. These tools often incorporate unique features or geometries designed to simplify the valve lash adjustment process for that particular engine. They may include integrated levers, locking mechanisms, or preset settings to ensure proper adjustment.

How a Gap Cam Works: A Step-by-Step Explanation

The operation of a gap cam, particularly the dial indicator type, involves a specific procedure to ensure accurate measurements.

Preparation: Before using a gap cam, it's crucial to ensure the engine is completely cold. This is because valve lash specifications are typically given for a cold engine, as thermal expansion will affect the gap size. Also, the engine must be in the correct position for each valve being measured. This generally involves rotating the crankshaft until the specific valve is in its fully closed position (often referred to as "base circle" or "heel" of the cam). The engine's repair manual will provide detailed instructions on how to achieve this for each valve.
Positioning the Gap Cam: The gap cam is carefully positioned over the valve stem, ensuring the dial indicator's probe is resting squarely on the rocker arm or other actuating component. The tool should be stable and secure to prevent movement during the measurement process.
Zeroing the Dial Indicator: Once the gap cam is in position, the dial indicator is typically "zeroed." This means setting the dial to read zero when the probe is just touching the rocker arm. This provides a reference point for measuring the valve lash.
Measuring the Valve Lash: The rocker arm (or other actuating component) is gently moved until it contacts the valve stem. The dial indicator will register the distance the rocker arm travels before contacting the valve stem. This distance is the valve lash.
Adjusting the Valve Lash (if necessary): If the measured valve lash is outside of the specified range, it needs to be adjusted. This typically involves loosening a locknut on the rocker arm and turning an adjustment screw to increase or decrease the gap. After making the adjustment, the locknut is tightened to secure the setting.
Verification: After adjusting the valve lash, it's essential to re-measure the gap to ensure it falls within the specified range. This process may need to be repeated several times to achieve the desired accuracy.

Benefits of Using a Gap Cam

While feeler gauges can also be used to measure valve lash, a gap cam offers several advantages, particularly in terms of accuracy and repeatability.

Increased Accuracy: Dial indicator type gap cams provide highly precise measurements, allowing for finer adjustments compared to using only feeler gauges. This is particularly important for high-performance engines or engines with tight valve lash tolerances.
Improved Repeatability: The dedicated fixture of a gap cam helps ensure consistent positioning of the measuring instrument, leading to more repeatable measurements. This reduces the chance of errors due to variations in technique.
Ease of Use (in some applications): For certain engine configurations, a specialized gap cam can simplify the valve lash adjustment process, making it easier to achieve accurate results, particularly for less experienced mechanics.
Reduced Risk of Error: Using feeler gauges incorrectly can introduce errors in valve lash measurement. Using a gap cam reduces these risks by ensuring more consistent and accurate measurements.

When is a Gap Cam Necessary?

While not always strictly necessary, a gap cam is a valuable tool in several scenarios.

High-Performance Engines: For engines where precise valve timing and valve lift are crucial for optimal performance, a gap cam is highly recommended.
Engines with Tight Valve Lash Tolerances: Some engines have very tight valve lash specifications, requiring a high degree of accuracy in the adjustment process. A gap cam can help achieve this.
Complex Valve Train Configurations: Engines with complex valve train designs, such as those with multiple valves per cylinder or variable valve timing systems, may benefit from the use of a specialized gap cam.
Routine Maintenance: Regularly checking and adjusting valve lash is an important part of engine maintenance. Using a gap cam can help ensure accurate and consistent adjustments, prolonging engine life and maintaining performance.

In conclusion, the gap cam, while not a camera in the traditional sense, is a valuable tool for accurately measuring and adjusting valve lash. Understanding its purpose and operation is essential for anyone working on internal combustion engines, especially those seeking to optimize performance and ensure engine longevity. The precision it offers makes it a worthwhile investment for serious mechanics and enthusiasts alike.