What is the normal valve clearance?

Valve clearance, or lash, is not universal. It depends on engine design and lifter type. In modern engines with hydraulic lifters, clearance is typically near zero, while engines with solid or mechanical lifters use a defined lash within the manufacturer’s specification. Always consult the owner’s manual or service manual for your exact model.

Understanding valve clearance

Valve clearance is the small gap between the valve stem and its actuating mechanism (rocker arm, cam follower, or lifter) when the valve is closed. The purpose of this gap is to allow for thermal expansion and ensure the valve seats properly when the engine heats up. Measurements are usually taken with a feeler gauge and adjusted according to the engine’s official spec. Different lifter designs—hydraulic, mechanical/solid, or shim-based systems—set different target clearances.

Why clearances differ

The choice of lifter design and valve train architecture governs the normal clearance. Hydraulic lifters automatically take up most slack during operation, yielding near-zero measured lash. Solid lifters and shim-based systems require a deliberate gap to prevent valve float and to accommodate temperature changes, so they list explicit ranges in the manual.

Typical ranges by engine type

The following ranges reflect common practices across many passenger cars and light trucks, but exact values vary by model and should come from the official service manual.

• Hydraulic lifters (most modern engines): near-zero clearance. Often specified as 0.00 to 0.05 mm (0.000 to 0.002 inches).


• Solid/mechanical lifters (adjustable lash): typically 0.10–0.30 mm (0.004–0.012 inches) for intake valves and 0.15–0.40 mm (0.006–0.016 inches) for exhaust valves. Exact numbers depend on the specific engine.


• Shim-based or bucket-style systems (variable clearance managed by shims): clearance values vary widely; set by the shim thickness to achieve the manufacturer’s spec for each valve.


• High-performance or older designs (varies): some engines use slightly larger or smaller lash within a defined range; always verify against the factory spec.

Because exact lash values depend on the engine design and temperature, always refer to the exact specification provided for your vehicle or engine family.

How to check and adjust valve clearance

To check and adjust valve clearance, follow these steps. The process differs for hydraulic versus solid lifters, and you should work with the engine cold and with the correct tools and manual guidance.

1. Consult the service manual to identify the correct lash specification for each valve (intake and exhaust) and note any model-specific procedures.


2. Ensure the engine is completely cold before taking measurements, as heat expands metal and changes lash.


3. Remove the valve cover to access the rocker arms, lifters, or cam followers for the cylinders you are checking.


4. Rotate the engine to top dead center (TDC) on the compression stroke for the cylinder you are testing and confirm the valve is properly positioned.


5. For hydraulic lifters: measure the lash with a feeler gauge if the manual instructs it; if the lash is outside spec, diagnose lifter issues or loss of preload, but generally hydraulic systems are not adjusted for lash.


6. For solid/mechanical lifters or shim-based systems: insert the appropriate feeler gauge between the rocker arm and the valve stem (or between the cam and lifter as specified). If the gauge does not slide with light drag, adjust by turning the adjuster screw or changing the shim thickness until the gauge fits with light drag.


7. After achieving the spec, reinstall the rocker cover, torquing bolts to specification, and recheck to confirm accuracy.


8. Repeat the process for all cylinders as required, then start the engine and listen for any ticking or abnormal noises, which could indicate an adjustment error or a faulty lifter.

Precise adjustment requires patience and correct torque on fasteners, plus fresh gaskets if you remove the valve cover. If you’re unsure, have a qualified mechanic perform the procedure to avoid valve seating problems or engine damage.

Units, references, and practical notes

Valve clearance figures are commonly given in millimeters and inches. Small discrepancies can be caused by temperature, instrument tolerance, and measurement technique. When in doubt, rely on the exact specification printed in your engine’s factory service manual and follow the manufacturer’s procedures to the letter.

Summary

Valve clearance is engine-specific and hinges on lifter design. Modern engines with hydraulic lifters generally run with near-zero lash, while engines with solid or shim-based lifters require a defined, model-specific gap. Always consult the official manual for your exact values, measure carefully with the correct tools, and adjust precisely if directed. Proper valve clearance helps ensure reliable valve sealing, optimal performance, and engine longevity.

Is more or less valve clearance better?

Ignoring valve adjustments can have dire consequences for your engine. Tight valve clearance can result in loss of compression, reduced power, and increased fuel consumption, while loose clearance can cause valve noise, poor idle quality, and even valve float, where the valves fail to close properly.

How to tell if valve clearance is bad?

Symptoms of bad valve clearance include engine noise like ticking or clattering, poor engine performance such as loss of power, rough idle, or misfires, and increased fuel consumption. If the clearance is too loose, you'll hear mechanical noises, while if it's too tight, the valves may not close completely, leading to performance issues.
 
Symptoms of loose valve clearance (too much gap)

• Engine noise: A loud ticking or clattering sound, especially from the top of the engine, due to parts like the tappets hitting the valve stems. 
• Reduced performance: In extreme cases, components can wear out or even become dislodged, and the valve will take longer to open, leading to poor engine performance. 
• Increased wear: This can cause excessive wear on components like tappets, pushrods, and valve stems. 

Symptoms of tight valve clearance (too little gap)

• Engine noise: A ticking or knocking sound from the upper part of the engine. 
• Poor performance: The engine may have a rough idle, misfire, difficulty starting, or a loss of power because the valve cannot close completely. 
• Burning valves: A valve that doesn't close properly can be burned by hot combustion gases, which can lead to a loss of compression, increased emissions, and even backfiring. 
• Increased fuel consumption: With a constantly open valve, the engine's efficiency is reduced, leading to higher fuel consumption. 

General symptoms of both problems

• Reduced power and acceleration: The engine may feel sluggish. 
• Increased fuel consumption: The engine uses more fuel than it should. 
• Excessive smoke: You may notice blue smoke from the exhaust, especially if a valve is burning. 
• Misfires or rough idle: The engine may not run smoothly. 

What happens if valve clearance is too high?

If valve clearance is too big, the engine will become noisy, performance will decrease, and components will experience excessive wear. The valve opens later and closes earlier than intended, shortening its duration and lift, which reduces efficiency and can lead to increased wear on the valve train.
 
Noise and wear

• Engine noise: A "ticking" or "clattering" noise is created as the parts of the valve train, like the tappets or rocker arms, make contact with excessive slack. 
• Increased wear: This excessive slack causes impact, leading to faster wear on components such as the tappets, rocker arms, and cam followers. 

Performance and efficiency

• Reduced performance: The engine will have less power because the valve doesn't open as far or as long, which creates less efficient combustion. 
• Decreased efficiency: On the intake stroke, a larger gap means the valve opens later and takes longer to open fully, which can lead to a less efficient mixture of air and fuel. 

Potential for more serious damage 

• Burnt valves: Although more common with too little clearance, excessive clearance can also lead to burnt valves by affecting the timing and combustion process, especially on exhaust valves which handle very high temperatures. 
• Component failure: In extreme cases, the excessive force or lack of proper valve timing can lead to more catastrophic failure. 

How to address excessive valve clearance

• Adjust the clearance: The proper solution is to adjust the valve clearance to the manufacturer's specifications.
• Check when cold: Always make sure the engine is cold before checking and adjusting valve clearances, as metal expands when it heats up. 

What is the recommended valve clearance?

With valve clearances set, as you would normally expect for a standard engine at 0.012-in, the engine idles very roughly. Shortly after release, Rover released a technical up-date stating the valve clearances should be set at 0.014-in on the inlets and 0.017-in on the exhausts.