If you’re diving into the world of engine building or maintenance, you’ve probably come across the term “valve shims.” These tiny, yet crucial components play a significant role in your engine’s performance and longevity. In this comprehensive guide, we’ll explore everything you need to know about valve shims, from their purpose to how to choose and install them correctly.
What Are Valve Shims and Why Are They Important?
Before we discuss the fundamentals of choosing and installing valve shims, let’s first understand what they are and why they matter.
Valve shims are thin, precisely measured discs that sit between the valve stem and the cam follower (or rocker arm) in an engine. Their primary purpose is to maintain the correct valve clearance, which is essential for proper engine operation.
Why is valve clearance so important? Well, it affects several aspects of your engine’s performance:
- Engine efficiency: Correct valve clearance ensures optimal fuel consumption and power output.
- Engine longevity: Proper clearance reduces wear on valve train components.
- Noise reduction: The right clearance minimizes valve train noise.
- Emissions control: Correct valve timing, influenced by proper clearance, helps control emissions.
Now that we understand their importance, let’s move on to the process of choosing the right valve shims for your engine build.
How to Measure Valve Shims
Before you can choose the right valve shims, you need to know how to measure them accurately. This process is crucial for determining the correct shim thickness needed for your engine.
Tools You’ll Need
To measure valve shims, you’ll need the following tools:
- Micrometer
- Feeler gauges
- Clean workspace
- Magnifying glass (optional, but helpful)
Step-by-Step Measurement Process
- Clean the shim: Ensure the shim is free from any dirt or debris that could affect your measurement.
- Use the micrometer: Place the shim between the micrometer’s anvil and spindle. Gently close the micrometer until it just touches both sides of the shim.
- Read the measurement: Most micrometers provide readings in thousandths of an inch or hundredths of a millimeter. Record this measurement.
- Double-check: It’s always a good idea to measure each shim at least twice to ensure accuracy.
- Measure multiple points: If possible, measure the shim at several points around its circumference to check for any inconsistencies.
Remember, accuracy is key when measuring valve shims. Even a small error can lead to improper valve clearance and potential engine issues down the line.
How to Calculate Valve Shims
Once you’ve measured your current shims and determined your valve clearance, you might need to calculate the thickness of new shims. Here’s a simple process to follow:
- Measure current clearance: Using feeler gauges, measure the current valve clearance.
- Determine desired clearance: Consult your engine’s manual for the recommended valve clearance.
- Calculate the difference: Subtract the desired clearance from the current clearance.
- Measure current shim: As we discussed earlier, measure the thickness of the current shim.
- Calculate new shim thickness: Add the difference from step 3 to the current shim thickness. This gives you the required thickness for the new shim.
For example, if your current clearance is 0.012 inches, the desired clearance is 0.008 inches, and your current shim is 0.100 inches thick:
- Difference: 0.012 – 0.008 = 0.004 inches
- New shim thickness: 0.100 + 0.004 = 0.104 inches
Remember, valve shims come in specific sizes, so you may need to round to the nearest available size.
How to Remove Valve Shims
Now that you’ve calculated the correct shim size, you’ll need to know how to remove the old shims. This process can be a bit tricky, especially if you’re new to engine work, but with patience and the right tools, you can do it.
Tools You’ll Need
- Valve spring compressor
- Magnetic pickup tool
- Clean rags
- Small container for storing removed shims
Step-by-Step Removal Process
- Prepare the engine: Ensure the engine is cool and the cylinder you’re working on is at top dead center (TDC) on the compression stroke.
- Remove necessary components: This typically includes the valve cover, camshafts, and possibly the cam followers, depending on your engine design.
- Compress the valve spring: Using the valve spring compressor, carefully compress the spring until the valve shim is accessible.
- Remove the shim: Use a magnetic pickup tool or a small screwdriver to carefully lift the shim out of its seat.
- Label and store: Immediately label the shim with its location and thickness, and store it safely.
- Clean the area: Use a clean rag to wipe away any debris from the valve bucket or shim seat.
- Repeat: Follow this process for each valve that needs its shim replaced.
Remember, organization is key when removing valve shims. Keeping track of which shim came from which valve will save you a lot of headaches later on.
Choosing the Right Valve Shims
Now that you know how to measure, calculate, and remove valve shims, let’s talk about how to choose the right ones for your engine build.
Factors to Consider
- Material: Valve shims are typically made from hardened steel or titanium. Steel is more common and less expensive, while titanium is lighter but pricier.
- Thickness: Shims come in a range of thicknesses, usually varying by 0.05mm increments. Choose based on your calculations.
- Diameter: Ensure the shim diameter matches your engine specifications.
- Brand: While aftermarket shims can be good, using OEM (Original Equipment Manufacturer) shims is often the safest bet.
- Surface finish: Look for shims with a smooth, even surface to ensure proper seating and function.
Tips for Choosing Valve Shims
- Buy a range: It’s often helpful to buy shims in a range of sizes around your calculated thickness. This gives you some flexibility during installation.
- Check compatibility: Always verify that the shims you’re buying are compatible with your specific engine model and year.
- Consider a shim kit: For a full engine rebuild, consider buying a complete valve shim kit. These often come with a range of sizes and can be more cost-effective than buying individual shims.
- Quality matters: Don’t skimp on quality when it comes to valve shims. Remember, these tiny components play a crucial role in your engine’s performance and longevity.
Installing New Valve Shims
Once you’ve chosen your new valve shims, it’s time to install them. This process is essentially the reverse of removal, but there are a few key points to keep in mind:
- Clean everything: Ensure the valve bucket, shim, and surrounding areas are spotlessly clean before installation.
- Check orientation: Some shims have a specific orientation. If this is the case, make sure you install them correctly.
- Seat properly: Make sure the shim is properly seated in the valve bucket. It should sit flat without any tilt.
- Recheck clearance: After installation, always recheck your valve clearance to ensure it’s correct.
- Lubricate: Apply a small amount of engine oil to the top of the shim before reinstalling the cam follower or rocker arm.
Maintenance and Longevity
Properly installed valve shims can last for a long time, but they’re not a “set it and forget it” component. Here are some tips for maintaining your valve shims:
- Regular checks: Include valve clearance checks in your regular maintenance schedule. The frequency will depend on your engine and usage, but every 20,000 to 30,000 miles is a common recommendation.
- Listen for changes: Unusual ticking or tapping noises from your engine could indicate valve clearance issues.
- Keep records: Maintain detailed records of your valve clearances and any shim replacements. This can help you spot trends and predict when adjustments might be needed.
- Use quality oil: Good quality engine oil helps protect your entire valve train, including your shims.
Conclusion
Choosing and installing the right valve shims is a crucial part of engine building and maintenance. While it might seem daunting at first, with the right tools, knowledge, and patience, it’s a task that many enthusiasts can handle.
Remember, the key steps are:
- Accurately measuring your current shims and valve clearance
- Calculating the required shim thickness
- Carefully removing old shims
- Choosing high-quality, compatible new shims
- Installing the new shims correctly
- Rechecking your work
By following these steps and maintaining your valve shims properly, you’ll be rewarded with an engine that runs smoothly, efficiently, and reliably for years to come.
Whether you’re building a high-performance racing engine or maintaining your daily driver, understanding valve shims is an valuable skill for any serious gearhead.
