Valve Clearance Adjustment Explained
As far as mechanical terms go, a valve clearance adjustment is commonly referred to as ‘adjusting the tappets’. Valve clearances are the small gaps between the tops of the valve stems and the part which presses on them to open the valves.
If your vehicle has become a little hard to start lately, or there’s a lack of horsepower, it’s probably time to check the valve clearances. The valves that control the air/fuel flow mixture and exhaust gases in your engine head are one of the most abused parts in the entire motor.
Under high revs, valve clearances can reduce as the valves and valve seats wear. As a result, you need to regularly inspect your vehicle’s valve clearances and adjust it if necessary.
What Are Valves And How Do They Work?
Valves play an important role in regulating any system and the seals are designed to be used in different types of engines for controlling oil consumption and valve lubrication. The correct design, manufacturing and maintenance of the seal are key to ensure performance and longevity.
Valves can be described as spring-tensioned inverted golf tees that are opened by lobes on rotating camshafts. This is either directly in overhead-cam engines or through pushrods acting on rocker arms in overhead-valve (pushrod) engines.
Over time and normal use, the clearances between the lobes or rocker arms and the valve stems can become greater. This often leads to a clattering noise or more engine vibration than you won’t recognise initially as it increases gradually. However, you would need a valve clearance adjustment to correct.
Types Of Valves
There are many different types of valves in various applications across virtually every industrial process. In terms of the automotive sector, we talk about exhaust valves and intake valves. The clearance of exhaust valves can become tighter over time as the valves or valve seats wear down. This will diminish the clearance, also known as the lash, between the valves and the valve train components.
Intake valves can also be affected as they open and close to let the air/fuel mixture enter the cylinders while the exhaust valves allow exhaust gases to escape. If there is too much or too little valve clearance, you will experience poor performance or a rough idle as the engine can no longer “breathe” normally and operate at peak efficiency.
With too much clearance, the valves will likely clatter and cause damage to the valves, camshaft lobes or rocker arms over time. When there’s not enough valve clearance, they won’t fully close which can cause excessive heat, resulting in reduction of engine power.
When Should I Get A Valve Clearance Adjustment?
It all depends on the vehicle’s age, mechanical condition and the brand. A valve clearance adjustment still applies to older vehicles but thanks to roller-follower valve train designs that reduce friction along with hydraulic tappets that help maintain optimal valve clearance, newer cars don’t need it often, if at all.
Always have your valves checked by an experienced, certified professional. It’s important to follow the manufacturer’s recommended intervals but how do you know when your valves need adjusting. An easy way to tell if you have a faulty valve seal is to perform a cold engine test. Here are some of the most common symptoms of bad valve seals:
- Not idling correctly causing bluish smoke from the exhaust
- The engine generates a loud clatter
- Consuming far more oil than normal
- Excessive levels of smoke beyond starting the engine
- Loss of power and acceleration
How To Check And Adjust Your Valves
In some cases, valves don’t generate any noise when there’s too much or too little clearance so mechanics won’t always know for sure that something is wrong without inspecting the valves.
Checking valve clearance includes the following:
- remove the valve cover or two valve covers on V-type engines
- measure the space between the intake valves and exhaust valves, along with their lobes or rocker arms using thin feeler gauges
- make sure the camshaft is in the proper position and each valve fully is closed for each measurement
Valve adjustments sometimes require installing or replacing shims using special tools. This is not a quick maintenance fix like changing the oil, especially on engines that have three or four valves per cylinder. You should expect to pay for at least a few hours labour and a charge for the inspection.
Valve Clearance Specifications
Not all vehicles have the same valve clearance specifications or procedures as it can vary among different manufacturers. The maintenance schedules for some newer Hyundai engines, for example, require a valve clearance inspection at 100,000 km while some Hondas need an inspection at 180,000 km.
However, some manufacturers recommend a valve clearance inspection only if there is excessive valve noise. Many don’t even mention valve clearance adjustment in their maintenance schedules whatsoever. Before doing anything, be sure to check your vehicle’s maintenance schedule in the owner’s manual.
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