Valve Clearance Calculator
This tool helps you determine the correct shim size needed to adjust your engine’s valve clearances. Accurate valve clearances are crucial for optimal engine performance, efficiency, and longevity.
Understanding Valve Clearance
Valve clearance, also known as tappet clearance or valve lash, is the small gap between the tip of the valve stem and the rocker arm or cam follower. This gap is essential because engine components expand when they heat up. Without adequate clearance, valves might not close fully, leading to:
- Loss of compression and power
- Poor fuel economy
- Overheating and potential burning of valves
- Rough idling
Conversely, excessive clearance can cause:
- Noisy valve train operation (tapping or clicking sounds)
- Increased wear on valve train components
- Slightly reduced performance due to altered valve timing
Adjusting valve clearance typically involves measuring the existing gap (when the engine is cold, unless specified otherwise by the manufacturer) and then replacing a small disc, called a shim, with one of a different thickness to achieve the manufacturer’s specified clearance.
How This Calculator Works
The calculation is straightforward:
- Determine the Difference: It subtracts the Specified Clearance from your Measured Clearance.
Adjustment Needed = Measured Clearance - Specified Clearance - Calculate New Shim Size: This difference is then added to your Current Shim Size.
New Shim Size = Current Shim Size + Adjustment Needed
For example, if your measured clearance is 0.15mm, the specified clearance is 0.10mm, and your current shim is 2.50mm:
- Adjustment Needed = 0.15mm – 0.10mm = 0.05mm (This means your gap is 0.05mm too large)
- New Shim Size = 2.50mm + 0.05mm = 2.55mm (You need a 0.05mm thicker shim)
If your measured clearance was 0.05mm (too tight) and specified was 0.10mm:
- Adjustment Needed = 0.05mm – 0.10mm = -0.05mm (Gap is 0.05mm too small)
- New Shim Size = 2.50mm + (-0.05mm) = 2.45mm (You need a 0.05mm thinner shim)
Note: Shims are usually available in specific increments (e.g., 0.05mm or 0.025mm). You’ll need to choose the available shim size closest to the calculated value. If the calculated value is exactly between two available sizes, consult your service manual or a trusted mechanic; often, aiming for the slightly looser side of the specification (if within the allowed range) is preferred over too tight.
Important Considerations
- Consult Your Service Manual: Always refer to your vehicle’s official service manual for the correct valve clearance specifications, adjustment procedures, and torque values. This calculator is a tool, not a substitute for proper documentation.
- Engine Temperature: Most valve clearance specifications are for a cold engine. Ensure the engine has cooled down completely before measuring.
- Accurate Measurements: Use quality feeler gauges and ensure they are inserted correctly (slight drag, not forced) for an accurate measurement. Measure multiple times if unsure.
- Correct Piston Position: Ensure the piston for the cylinder you are working on is at Top Dead Center (TDC) on the compression stroke (or as specified in your manual) so both valves are fully closed.
- Shim Availability: The calculator provides a precise mathematical result. You will need to select the closest available shim size from your supplier.