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Tappets, tows (roller finger follower), and rocker arms are important components of the valve system in internal combustion engines. These components work together to transfer the movement of the camshaft to the valves, ensuring precise timing and efficient airflow into and out of the combustion chamber. Tappets (also known as pushers) are located between the camshafts and the valves in overhead camshaft engines, or between the camshafts and the push rod in flathead engines. Rocker arms act as a rocker bridge between the pushrod and the valve stem. Good lubrication and wear resistance are essential, as these components operate under high loads. Brands such as Kolbenschmidt offer durable, OE-quality replacement parts for these critical systems. |
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Tappet noise, often described as a ticking or tapping sound from the top of the engine, isn’t always a cause for alarm. In some engines, especially those with hydraulic lifters, mild noise during cold starts can be normal. However, persistent or loud tappet noise may indicate wear, improper valve lash, or oil starvation. If ignored, it can lead to camshaft scoring, rocker arm damage, or premature valve wear. It is crucial to maintain the correct oil quality and oil supply, as insufficient lubrication is one of the main causes of damage to the valve system.
Several factors can cause tappet noise, including worn tappets, low oil pressure in hydraulic tappets, heavily contaminated oil, or incorrect valve clearance. In engines with mechanical tappets with valve stem plates, the valve clearance may need to be checked. Other factors that can contribute to this are wear in the tappet guides, push rod tubes, or rocker arm bridge bearings. Hydraulic tappets can also fail due to internal sludge formation or clogging, especially if oil changes are neglected. In engines with fixed tappets, excessive clearance between the parts will lead to noticeable noise.
Adjustment is only required for engines equipped with solid (mechanical) tappets—hydraulic lifters are self-adjusting. For mechanical tappets, adjustment intervals vary by manufacturer but generally fall between 20,000 and 50,000 kilometers. Symptoms of misadjustment include noisy operation, rough idle, or loss of power. When adjusting, it’s essential to follow the correct procedure and specifications, as incorrect valve lash can cause long-term damage.
Replacing tappets (lifters) typically requires removing the rocker arm assembly, pushrods, and sometimes the camshaft, depending on engine layout. After gaining access, old tappets are removed and replaced with compatible units, ensuring all surfaces are clean and well-lubricated during installation. It’s important to inspect associated components like the pushrod guide and cam lobes for wear. Failure to address underlying issues can result in premature failure of the new tappets.
Rocker arms act as a rocking lever between the pushrod and the valve. When the camshaft pushes on the tappet, the pushrod transfers that motion to the rocker arm, which then presses down on the valve stem to open it. Rocker arms typically rotate on a rocker arm shaft and rely on rocker arm bushings, bolts, and bridges to stay aligned and secured. Some modern systems also include a rocker arm oil control valve, which adjusts lift and timing. Proper fit and clearance are crucial to maintain engine performance.
Common symptoms of a failing rocker arm include knocking noises, engine misfires, irregular idling, or loss of power. Physically, a defective rocker arm may show cracks, play on the shaft, or excessive wear in the bushing or on contact points. Metal debris in the oil can also be a warning sign. If ignored, a defective rocker arm can cause valves to float or even break, leading to serious engine damage. It is highly recommended to replace worn rocker arms with high-quality parts from Kolbenschmidt, for example.
The adjustment varies depending on whether the engine uses hydraulic or mechanical tappets. For mechanical tappets, use a feeler gauge to set the correct valve clearance. Hydraulic tappets must be depressurized before installation to remove any air bubbles and test oil. Then place the tappet in a container of clean oil, where it will soak up oil without air pockets as it springs back. Correct procedure prevents noise from the valve system and ensures consistent performance. Use a torque wrench to tighten the rocker arm bolts and check the condition of the rocker arm bridge and shaft at the same time.
