When most people hear the term “valve lash,” they wonder where it is located. Is it close to the valve in the head cylinder or engine block? Valve lash is related to the valves in the head cylinder, but it is not an engine component or part.
A valve lash is a gap between valve trains in the head cylinders that ensures the engine runs as predetermined by the manufacturer. If the lash is set incorrectly or changes, the engine will not run smoothly and may even lead to expensive repair issues.
This article will throw more light on valve lash meaning, causes, symptoms, and how to set it. But, most importantly, you’ll learn why valve lash is necessary.
What is Valve Lash
The valve lash is the empty space between the engine’s valve train parts. It is commonly known as valve clearance.
Valve lash measurement area differs from vehicle to vehicle, based on engine design. For instance, on overhead camshaft engines, the measurement is taken between the camshaft follower and the camshaft or between the tappet and the camshaft. On the other hand, On Overhead valve engines, it is the space between the rocker arms and valve stems.
The proper valve clearance varies depending on your engine design. The specified valve clearance on your engine is available online and on the vehicle service manual.
Vehicle engines comprise several components that work in harmony to effectively and quickly meet up with the required load. For example, the intake and exhaust valves must open and close as predefined by the manufacturer for optimal engine performance. And, they will stay in open and closed positions when it is due.
In any case, the multiple components in the engine make it generate heat despite the proper functioning of the cooling system. And when these metal components get hot, it expands.
Valve clearance ensures that the cam lobes have enough valve openings. We mentioned above that metals expand when they get hot. Valve lash is essential for this purpose. It compensates for thermal expansion by preventing heated components from rubbing against each other. If not, the friction between these components can cause accelerated wear and lead to catastrophic engine breakdown.
Again, the valve clearance ensures that the valves are properly closed on the camshaft lobe low segment. As a result, it ensures there’s no leak that may reduce engine power and lead to poor power output.
Symptoms of valve lashing
You’ve seen the importance and meaning of valve lash. Now, let’s look at the common valve lash symptoms you should watch out for. Recognizing these will help you notice when the valve lash is incorrectly set and make the necessary adjustment before it escalates to severe repair jobs.
Loud tapping or clicking noise
A common sign of valve lash clearance that needs adjustment is a loud tapping or clicking noise from the top cylinder. The loud noise typically comes from the friction within the head cylinders. If you ignore this sign and continue driving for an extended period, the engine will lose power over time.
This is a sign you need valve lash adjustment. If the valves are not adjusted properly, they will close slower than meant to be, causing the engine to dissipate heat at a slower than usual. If this happens, the engine will overheat. However, it is fair to say there are other common probable causes of an engine overheating.
Bad gas mileage
If valves are out of adjustment, they’ll cause the engine to use more gas. A bad valve clearance may cause the exhaust valves to open while the intake valves are still open and taking in the air-fuel mixture. By this, some amount of fuel could enter the engine and exist through the exhaust without going through the combustion cycle.
Incorrect valve lash on 6.7 Cummins and other engines can cause pre-ignition. Pre-ignition is the premature combustion of the air-fuel mixture in the combustion chamber.
When the valve lash is out of adjustment, the engine will have increased friction, leading to excessive heat. If the heat buildup gets too much, premature combustion of the air-fuel mixture will occur in the combustion chamber.
As explained above, the valve lash will create increased friction if it goes out of adjustment. This will lead to accelerated wear on the valve and other components and may eventually cause damage. In addition, if the space between the lifters and the valves is much, many components in the head cylinder will experience shock and strange noise. This can damage several components in this engine segment.
What causes valve lashing?
Some engines require periodic valve lash adjustment. In these engines, the valve lash will go out of specification if you do not adjust them as scheduled.
A common cause is wear and tear. If you notice excessive valve clearance on engines with non-adjustable valve lash, examine the valve trains for wear.
Another cause of valve lashing is erosion. Valve lash can shrink. So, inspect the seats for erosion if you have valve lashing on non-adjustable engines. If the seats wear out, the valves will go up higher than predetermined by the manufacturer.
How to Set Valve Lash
Let’s point this out; some car valve lashes are non-adjustable. For example, engines with valve lash hydraulic lifters are non-adjustable. This is because they have built-in automatic valve lash adjustment. On the other hand, engines with solid lifters are adjustable and require scheduled adjustment.
Most DIYers and drivers do not have the skills and tools to adjust their valve lash when it goes out of adjustment. However, you can set the valve lash at home with the right guide, a specific repair manual, or an online database to get your manufacturer’s specifications.
Determine the lifter in your engine
Uncover the valve cover and determine the type of lifter in your engine. You can also get this information from your specific-car service manual. There are two types of lifters – hydraulic and solid lifters.
Engines with hydraulic lifters do not require periodic lash adjustment. They have built-in automatic adjusters that save time and money.
If your vehicle has solid lifters, you need to check the valve clearance and adjust them periodically as the manufacturer recommends. These lifters need manual adjustment to maintain optimal engine performance.
Remove the valve cover and inspect the valves when sitting in a close position and laying on the cam lobe. Get a feeler gauge and measure the space between the appropriate components. Adjust the valve clearance accordingly if it is too small or too big.
It will be challenging to set a valve lash without a visual presentation, especially if you haven’t done it before. Watch this video for a visual clarification on how to set 6.7 Cummins valve lash and other diesel engines manufactured from 2000 upwards.
Q: Do you adjust valves to hot or cold?
Only adjust your valves when the engine is cold. It is appropriate to correct the valve lash that is causing slight power loss, idle misfire, and loud noise only when the engine is completely cooled. Valve lash can cause excessive friction and power loss and even cause catastrophic damages if ignored or not properly set. So, you don’t want to take chances.
Q: What happens if your valve lash is off?
If your valve lash is off, the engine performance will drop because the engine is not breathing properly. Imagine what happens when your nose is partially blocked, and you can’t breathe with your mouth.
And, some exhaust gas will escape from the engine when it’s not yet time to get out of the engine. This can lead to severe engine breakdown. You may experience high fuel consumption and increased exhaust gas from the tailpipe.
Q: What should valve lash be set to?
The thermal gap between the rocker arm and the valves is generally very small, around 0.1 to 0.4 mm. The gap is typically measured with valve lash tools (feeler gauge) in increments of 0.05 mm or less.
The specified gap difference between the intake and exhaust valves differs. It also differs from engine to engine. Therefore, consult your service manual to determine where the valve lash should be.
Q: What does adjusting valve lash do?
Valve lash adjustment ensures that the opening and closing of the valves and the combustion process occur without any issues. If the valve lash is too loose or tight, it will cause catastrophic damage. Valve lash adjustment prevents this damage from occurring.
Q: Can tight valves cause low compression?
Tight valves will open sooner, wider, and stay open longer. This will invariably cause low compression due to valves not sitting when they should. However, some experts may have different opinions about this.
Q: Can valve clearance cause no start?
Yes, incorrectly adjusted valves can cause a hard start or no start conditions. If the valve lash is reduced to nothing due to wear, the valve will stay open slightly and reduce engine compression. This no-start situation commonly happens when the engine is cold as opposed to when hot because once the engine gets hot, the metal components expand.
Q: Is it better for valves to be loose or tight?
Too tight can be dangerous because if they are too tight, they won’t sit properly and burn up. The valves get cooled from having contact with the seat. Loose is better than tight, but too loose can be dangerous. It can damage the cams and the valve tips because you’re hammering them instead of pushing them.
Q: How often should you check valve lash?
You should check your mechanical valve lash every 30,000 to 60,000 miles. There are bogus recommendations on this interval from experts and car manufacturers. Some manufacturers recommend 60,000, while others make a bogus claim of around 105,000 miles. Always consult your service manual for your manufacturer’s recommendation.
Q: How much does it cost to fix valve lashing?
The cost of fixing a valve lashing depends on your vehicle type, region, and the service technician handling the repair. However, the average cost of fixing a valve lashing is between $200 to $300. This is an estimated cost. Therefore, it can be lower or higher.
Valve lash, out of adjustment, reduces the engine efficiency. It can escalate to severe problems if ignored for an extended period.
So, if you notice any of the symptoms above, consult a professional technician to track the prime cause and fix it before it escalates. I recommend you have a mechanic fix it. Do not start practicing DIY skills with valve lash issues.