Rocker Arm Buyer's Guide
- In some engines, what pushes the valves down to allow the passage of air, fuel, or exhaust into or out of the cylinder is the rocker arm.
- Serving as a mechanical link between the camshaft and the poppet valve, the rocker arm translates the rotation of the camshaft into the linear motion that moves the valve.
- The design of the rocker arm depends on the type of the valve train. Rocker arms for overhead valve (OHV) engines include stamped steel, roller tipped, full roller, and shaft, while overhead camshaft (OHC) engine rocker arms are center pivot and end pivot or finger follower.
- Bad rocker arm symptoms include an illuminated check engine light, poor engine performance, and rocker arm noises.
- At CarParts.com, rocker arm replacement costs from anywhere around $8 to $235. These can be bought individually, in sets, or in kits.
Internal combustion engines, whether gasoline or diesel, require air and fuel to create an explosion that will move the pistons and generate energy. There should be adequate amounts of each of the elements to ensure that the ratio is ideal for optimum combustion. The air and fuel, therefore, need to be fed to the engine in a controlled manner. There should also be a way to remove the spent fuel from the engine.
The valve train assembly is what controls the entry of air and fuel into the engine and the exit of exhaust gas. This system typically includes valves with springs and a mechanism that moves the valves. Depending on the engine, the valve actuating mechanism could be a camshaft connected to rocker arms or solenoids.
What is a Rocker Arm?
In some engines, what pushes the valves down to allow the passage of air, fuel, or exhaust into or out of the cylinder is the rocker arm. The engine rocker arm is a reciprocating lever that has one end that connects to the valve while the other connects to the camshaft. Often, the rocker arm is made of metals such as iron, steel, and aluminum.
What Does a Rocker Arm Do?
Serving as a mechanical link between the camshaft and the poppet valve, the rocker arm translates the rotation of the camshaft into the linear motion that moves the valve. The camshaft features flat oval lobes, and when the nose or the protruding part is turned towards the rocker arm, the lever is pushed either up or down. Meanwhile, the other end of the rocker arm moves the valve in the open or closed position.
When the lobe nose is turned away, the rocker arm is freed from the influence of the camshaft and the spring around the valve stem resets the position of the valve and the rocker arm. With the cam lobe and the spring, the rocker arm oscillates or rocks between the camshaft and the valve.
Types of Rocker Arms
The design of the rocker arm depends on the type of the valve train. The major types of valve trains are the cam-in-block such as the overhead valve (OHV), overhead camshaft (OHC), and camless. Some valve trains make use of rocker arms. In these valve trains, the components and their positions determine the type of rocker arms to be used.
OHV Rocker Arms
Another name for OHV engines is pushrod. This type usually has the camshaft in the engine block while the valves are on the cylinder head on the top of the engine. Due to the location of the camshaft and the valves, a pushrod is needed to connect the rocker arm to the cam lobe.
The simplest type of rocker arm, the stamped steel rocker arm is named after the process by which it is made. This type of rocker arm is constructed from a piece of steel that is pressed onto and shaped by a die. It features a trunnion pivot and is secured with a rounded nut.
Named for its feature, the roller tipped rocker has a free-spinning metal cylinder on its valve-end side. With a roller tip, friction and wear are minimized allowing for more power. Roller rockers could either be made from stamped metal or machined steel or aluminum. It also has a trunnion pivot and a stud nut.
In addition to having a roller tip, a full roller rocker arm features a shaft with bearings in place of a trunnion pivot. The use of bearings further lessens the amount of friction compared to roller tipped rocker arms. Full roller rocker arms are often made from machined steel or aluminum.
When two or more full roller rocker arms are attached to a single rod, it is then called a shaft rocker arm. The rigid shaft helps keep the rocker arms stable during high engine revolutions.
OHC Rocker Arms
In OHC engines, the camshaft and valves are all located on the cylinder head. Since the camshaft and valves are close to each other, there is no need for pushrods. This engine type could either have a single overhead camshaft (SOHC) or a double overhead camshaft (DOHC) configuration. With an SOHC, only one camshaft actuates the valves, while with a DOHC, there is a separate camshaft for the intake and exhaust valves. In some OHC engines that do not have rocker arms, the cam lobes have direct contact with the valves.
The center pivot rocker arm gets its name from the location of its fulcrum. It could have a roller tip that connects to the cam lobe instead of the valve or have a follower in place of a push rod.
End Pivot or Finger Follower
In an end pivot or finger follower rocker arm, the fulcrum is located on the tip of the lever opposite the valve. With this configuration, the cam lobe pushes down on the middle of the rocker arm.
Bad Rocker Arm Symptoms
Due to its function, it is important to know if the rocker arms are still in good working condition or have started to wear out. However, since it affects the opening and closing of the intake and exhaust valves, the signs of a broken rocker arm could be mistaken for symptoms of another malfunctioning engine component.
Illuminated Check Engine Light
When the vehicle's systems detect an irregularity in the performance of the engine, the check engine light comes on. A failing rocker arm could affect how the engine runs and trigger the check engine light.
Poor Engine Performance
Since the rocker arms are what transfer the movement of the camshaft to the valves, any problem with the rocker arms could affect the engine's intake and exhaust. If the valve timing or the air-fuel ratio in the cylinder are off, the engine might generate less power. This could result in poor acceleration or stalling.
Rocker Arm Noise
When there are any issues involving the valves, these could make rapid clicking, tapping, or ticking noises. With broken or poorly lubricated rocker arms, the valves might not be able to open and close properly.
Using an on-board diagnostic (OBD) scan tool could help determine whether the problems with the engine are due to faulty rocker arms. Getting diagnostic trouble codes (DTCs) P2646 for "A" Rocker Arm Actuator System Performance/ Stuck Off (Bank 1), P2647 for "A" Rocker Arm Actuator System Stuck On, and P2662 for "B" Rocker Arm Actuator System Stuck On could mean issues with the rocker arms.
Rocker Arm Replacement
It is important to have the rocker arms replaced immediately when they become broken. Disregarding the issue could result in more serious damage to the engine and higher repair costs.
Taking note of your vehicle's make, model, and year could help you find exact replacements more easily. Getting rocker arms that do not match your car's engine could affect its performance.
At CarParts.com, rocker arm replacement costs from anywhere around $8 to $235. These can be bought individually, in sets, or in kits.
Auto Upgrade 101: Finding the Right Rocker Arms
With the right set of rocker arms, your auto will definitely rock the road and rule the highway. Rocker arms help produce the force needed to move the pushrods while pushing down the valves. Should you decide to upgrade your rockers, you have to know which type suits your engine, budget, and application to make shopping faster.
What are the types of rocker arms?
Before deciding to purchase a rocker, you have to know if its type and dimensions meet the specifications of your vehicle. Selection is usually based on the ratio of your engine camshaft and heads to the size of your rockers, so knowledge about the specs of your auto is important. Here are the types of rockers:
Stamped steel rocker arms: Rocker arms made of stamped steel are widely used because of their affordability and accessibility. Most stamped steel arms are designed to fit all makes and models.
Roller tipped rocker arms: Though they are similar to stamped steel rockers, roller tipped arms are different they have roller tips at the end of the valve to produce less friction and wear. Some drivers prefer these rockers because they've got more power than stamped steel ones. Roller tipped rockers are used in many race cars, including customized Ford Mustangs and Chevy Corvettes.
Full roller rocker arms: Vehicles with high-revving engines like customized Chevy Corvettes and Toyota 4Runners usually require full roller rocker arms. Unlike stamped steel and roller tipped rockers, these are manufactured using machined steel or aluminum.
Shaft rocker arms: Shaft rockers are practically built off of full roller rockers, but the two types differ in design. Shaft rockers are more stable than full roller ones because they are connected by a common shaft that increases valve train stability. These are used in high-performance automobiles from various makes like Honda, Chevrolet, and Ford.
What should I look for when purchasing rocker arms?
Apart from the type, you should also take note of the pricing, specs, and additional features offered by each product.
Price: Generic rocker arms that do not include special features usually cost less than $50. If you need a basic rocker as replacement for a damaged one, you can check out Auto 7, Omix, and OES Genuine product lines.
But if you plan to upgrade your factory rocker arms, be prepared to spend at least $200 for specialized products. You can check out Comp Cams line of rockers; these components can create power gains up to 30 hp. Proform also offers performance rocker arms that are a little cheaper than Comp Cams'.
Location: Make sure you know the specs of your auto so you can get the replacement that fits the location of your original rockers. Find out if it is installed in the intake side, lower or upper area, front or rear, etc.
Product fit: You can choose between aftermarket stock and OE replacement. OE replacements are generic parts that suit most automobiles while aftermarket parts usually improve the engine design ratio for bigger hp gains.
How to Upgrade Your Mustang's Rocker Arms
With the right set of rocker arms, you can enjoy powerful horsepower gains and high engine performance. Rocker arms help produce the force needed to control the opening and closing of your exhaust intake valves. This guide will help you complete your rockers' upgrade (this is applicable only to Mustang vehicles).
Difficulty level: Difficult
Things you'll need:
- Valve cover gasket
- Socket set
- Gasket sealer
Step 1: Allow your engine to cool down before you start. Use the wrench to loosen the terminal nut and disconnect the negative cable from the battery. Get the screwdriver and loosen the clamp of your air cleaner duct. Disconnect all the other cables, hoses, and brackets until you reach the valve cover. Remove the cover to access the valve train.
Step 2: Uninstall the stock rocker arms by removing the nut holding them at the center. The Mustang's engine typically has 16 rocker arms; eight arms are placed on top of every cylinder head.
Step 3: Place the new set of rockers on top of the cylinder head; the metal roller should be sitting on top of the valve, not on top of the pushrod. Tighten each rocker arm's single retaining nut to complete the adjustment process.
Step 4: Reinstall the valve cover gasket. Apply the gasket sealer along the lip of the valve cover then press the gasket into place. Apply another bead of gasket sealer to the opposite side of the valve cover gasket. Grab the torque wrench to tighten the valve cover's retaining bolts to 10 ft.-lb. of torque.
Step 5: Reconnect the hose to the PCV valve and reinstall all the brackets, nuts, cables, screws, and clamps that you removed.
- For engine builders, you can move the pushrod closer to the pivot point of the rocker to increase rocker ratio.
- It is advisable to use roller rockers for Mustang vehicles because these produce less heat and friction.
- Check your rocker arm geometry; the tip of the valve should be right at the center.