Valve shims play a crucial role in maintaining the optimal function of your engine’s valves, particularly in high-performance and high-revving engines. Proper valve shim adjustment can impact everything from engine power and efficiency to overall longevity. In this article, we’ll explore what valve shims are, the purpose of valve spring shimming, and how understanding and adjusting engine valve shims can benefit your vehicle’s performance.
What is a Valve Shim?
Understanding the Basics of Valve Shims
A valve shim is a small, precisely machined metal disc or spacer that sits between the camshaft and the valve in an engine. Valve shims help maintain the proper clearance, or “lash,” between these components. This clearance is critical because it ensures the valve opens and closes correctly, allowing the engine to “breathe” properly by controlling airflow into and out of the combustion chamber.
Purpose of Valve Shims in an Engine
The main purpose of a valve shim is to regulate valve clearance, ensuring that the engine’s valves open and close with precise timing. Without proper clearance, the engine may suffer from reduced performance, increased wear, and even valve or camshaft damage. In high-performance engines, or those that regularly operate at high RPMs, correct shim thickness is crucial to prevent excessive wear or heat buildup.
What Are Valve Spring Shims Used For?
Role of Valve Spring Shimming
Valve spring shimming is the process of adding shims to the base of the valve springs to adjust the installed height or pressure of the springs. Valve spring shims allow for precise adjustment of spring pressure, which helps maintain proper valve function, especially in performance engines where valve control at high RPMs is essential.
In engines with aggressive camshafts, which often open the valves more rapidly, the extra pressure from valve spring shimming helps prevent “valve float” (when the valve doesn’t close fully). This control of valve movement improves the engine’s ability to sustain high RPMs without misfires, protecting the valves and ensuring efficient combustion.
Benefits of Valve Spring Shimming
Valve spring shimming improves the reliability and durability of the engine by ensuring the correct valve spring tension. The benefits include:
- Prevents Valve Float: Valve float can lead to poor engine performance and even valve damage.
- Enhances Engine Response: Proper spring pressure contributes to smoother valve operation and improved throttle response.
- Improves Engine Longevity: By keeping the springs at the right tension, valve spring shimming reduces wear on both the springs and the camshaft.
How Valve Shim Sizes Affect Engine Performance
Importance of Proper Shim Sizing
The size of the valve shim directly affects valve clearance, and even a small deviation in thickness can make a noticeable difference in how the engine performs. If the shim is too thick, it will reduce clearance, preventing the valve from fully closing, which can lead to compression loss, power reduction, and overheating. Conversely, if the shim is too thin, it increases the clearance, causing the valve to open later and close sooner, impacting timing and engine efficiency.
Consequences of Incorrect Valve Shim Sizes
Incorrect valve shim sizes can lead to several performance issues, including:
- Power Loss: Poor valve timing from incorrect shim sizes disrupts the air-fuel mixture and affects combustion, leading to noticeable power loss.
- Increased Wear: Incorrect shim sizing causes the camshaft and valves to collide or “slam” together, increasing wear and reducing component lifespan.
- Overheating: If valves don’t close properly due to incorrect shimming, the engine can overheat from continuous heat exposure in the combustion chamber.
Signs Your Engine May Need Valve Shim Adjustment
Symptoms of improper valve shim sizes or clearance issues include:
- Tapping or Clicking Sounds: Noisy valve operation can signal excessive clearance, requiring shims to restore proper spacing.
- Loss of Power: Reduced power, especially at high RPMs, often indicates improper valve timing due to incorrect shimming.
- Increased Fuel Consumption: Poor timing caused by improper valve shimming can lead to inefficient combustion and increased fuel usage.
How to Perform a Valve Shim Adjustment
What is Valve Shim Adjustment?
Valve shim adjustment is the process of changing or modifying the valve shims to achieve the correct clearance between the camshaft and valve. Adjustments are usually performed by removing the valve cover, measuring the clearance with a feeler gauge, and swapping shims if necessary to achieve the desired spacing.
Regular valve shim adjustments are important, especially in high-performance or older engines, where clearances can change over time due to wear. A proper valve shim adjustment can restore lost power, improve fuel efficiency, and extend engine life.
Steps to Adjust Valve Shims
- Access the Valve Cover: Remove the valve cover to access the valve train and the camshaft.
- Measure Clearance: Use a feeler gauge to measure the clearance between the camshaft lobe and valve.
- Determine Shim Size: Compare the measured clearance with the recommended specification for your engine. If it’s out of spec, calculate the required shim thickness.
- Replace Shims as Needed: Remove the camshaft or rocker arm, replace the shim with the correct thickness, and reassemble.
- Recheck Clearance: After reassembling, measure the clearance again to ensure it falls within specifications.
Due to the technical nature of valve shim adjustment, it’s usually recommended to have a professional perform the adjustment, especially if you’re unfamiliar with engine work.
Engine Valve Shims: Material and Durability
Materials Used for Valve Shims
Engine valve shims are typically made from hardened steel or other durable materials that can withstand high temperatures and pressure. The shim’s material affects its durability and resistance to wear, especially in performance engines that generate higher heat and stress.
Quality shims are essential, as softer or lower-grade materials may wear out faster, impacting valve clearance and requiring frequent adjustments. Investing in high-quality shims ensures that the valve clearance remains stable for longer periods.
Durability and Maintenance of Valve Shims
While valve shims are highly durable, they can still wear over time, especially in engines with frequent high-RPM usage. Routine inspection and maintenance of the valve shims and springs can help detect wear early, allowing for timely replacement before it affects engine performance.
When to Consider Valve Spring Shimming and Valve Shim Adjustment
High-Performance Engines
For high-performance or modified engines, valve spring shimming and valve shim adjustments are often necessary to ensure stability under increased RPM and stress levels. High-performance engines benefit from increased valve control, which reduces the risk of valve float and optimizes timing.
Older Vehicles and Routine Maintenance
In older vehicles, valve clearance can gradually change as parts wear. Regular valve shim adjustment can help these engines maintain performance and fuel efficiency over time. It’s especially important in vintage or classic cars, where engine parts may no longer fit as precisely as when new.
Engines with Upgraded Camshafts
Installing an upgraded or high-lift camshaft often changes the requirements for valve spring pressure and valve timing. In these cases, both valve spring shimming and precise shim adjustments are recommended to align the upgraded camshaft’s profile with the valve movement, optimizing performance and durability.
Final Thoughts
Valve shims and valve spring shimming are essential for maintaining proper valve operation and protecting your engine from excessive wear. Understanding what are valve spring shims used for and the importance of regular valve shim adjustment can help drivers and car enthusiasts keep their engines in peak condition. Proper shim sizing ensures optimal valve timing, reduces wear, and can improve performance, especially in high-stress or high-performance applications.
For those seeking to maintain their vehicle’s performance and engine health, regular checks on engine valve shims and, if necessary, adjustments are a worthwhile investment. Whether you’re a seasoned mechanic or taking your vehicle to a professional, knowing how these small components impact overall engine function can help ensure your engine runs efficiently for years to come.
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