Camshaft Buyer’s Guide
- Made of cast iron or hardened steel, a camshaft is basically a rod with oval-shaped bulges known as cams or lobes.
- As the shaft rotates, the pointy ends or high spots on the cams come in contact with the rocker arms or valve lifters, which push the valves to open at precise times throughout the cycle.
- The camshaft opens and closes the intake and exhaust valves in time for the pistons’ up-and-down strokes.
- Over time, the lobes can be wiped out or flogged and the lifters can get worn, which will make it difficult to open the valves.
- Camshafts can also seize or may break due to a manufacturing defect or poor engine maintenance. When the camshaft starts to fail, you may hear some popping sounds or backfiring coming from the tailpipe or intake; you may also notice some tapping noise from the valve cover.
- A broken camshaft will not only affect engine performance but will also cause damage to the cylinder head, valves, pistons, and other parts of the engine if left unchecked.
An internal combustion engine has thousands of moving parts. These moving parts must be well-choreographed to spin, flex, shift, open, or close at a specific moment or to a precise rhythm. With synchronized movements, the engine can take in just the right amount of air and fuel, burn the mixture, and produce massive amounts of energy that can be converted into motion. Timing and precision are crucial to efficient fuel combustion.
When burning fuel, the intake and exhaust valves must open and close at a specific time and order according to the position of the pistons, which are linked to the crankshaft through the connecting rods. The camshaft rotates along with the engine crankshaft to open and close the intake and exhaust valves.
As the piston goes down for the intake stroke (also known as top dead center), the intake valve must open to let the air-fuel mixture enter the cylinder where it is compressed and ignited and must close as the piston bottoms out (also known as bottom dead center). This is when the exhaust valve will open to expel combustion gases after the mixture has been burned and will close once the piston is done with its exhaust stroke. How fast the valve will open and close and how wide it has to stay open will all depend on the engine load and speed. Proper valve timing cannot be achieved if the camshaft, which basically controls the valves, is failing.
What is a camshaft?
Made of cast iron or hardened steel, a camshaft is a rod with oval-shaped bulges known as cams or lobes. The pointy ends of the lobes are arranged in different angles along the length of the shaft. As the shaft rotates, these pointy ends or high spots on the cams come in contact with the rocker arms or valve lifters, which push the valves to open at precise times throughout the cycle.
Since the valves are spring-loaded, they will close on their own as the spring pulls back to its original position. The number of lobes and the length of the shaft vary depending on the valvetrain layout and the cylinder arrangement of the engine. A single overhead cam (SOHC) engine is equipped with one cam per head, while a dual overhead cam (DOHC) engine uses two cams per head.
Where is the camshaft located?
On earlier engine designs, the valves are located in the head, whereas the camshaft can be found near the bottom of the engine, within the engine block. In modern overhead-cam engines, the camshaft is positioned above the cylinder banks or within the cylinder head near the top of the engine.
What does a camshaft do?
The camshaft is driven by the engine crankshaft through a toothed rubber timing belt or a metal roller timing chain that wraps around the sprockets. In a two-stroke engine, the camshaft rotates at the same speed as the crankshaft, while in a four-stroke engine, the camshaft spins at half the speed of the crankshaft since the camshaft gear has twice more teeth.
The rotation of the camshaft is synchronized with the revolution of the crankshaft, so the valves’ timing will be controlled accurately along with the pistons’ up-and-down strokes. Some camshafts use what they call a variable valve timing (VVT).
Hydraulic actuators are used to adjust the timing according to the angle or position of the crankshaft. Meanwhile, other camshafts are designed with a specialized variable valve lift (VVL) that allows the engine control module (ECM) to switch between valve lift options.
The camshaft must open and close the valves at specific intervals to control the volume of air and fuel that flows into the combustion chamber and to force out exhaust gases in time for the next cycle or charge. The camshaft has four strokes: intake, compression, power, and exhaust. If all these are done at the right moments, the engine can generate power more easily at varying speeds and under different operating conditions. Needless to say, the camshafts have a huge impact on engine performance. In some vehicles, the camshaft is even used to drive the oil pump, fuel pump, distributor, and power steering pump.
Why do camshafts fail or go bad?
Even if the camshaft is made of solid steel, it is still prone to wear and breakage after the vehicle has been driven for years. The lobes can be wiped out or flogged and the lifters can get worn, which will make it difficult to open the valves. Camshafts can also seize or may break due to a manufacturing defect or poor engine maintenance.
When the camshaft starts to fail, you may hear some popping sounds or backfiring coming from the tailpipe or intake. You may also notice some tapping noise from the valve cover. The engine may suffer from what they call a dead miss and may struggle to produce sufficient power. If one of the lobes drives a high-pressure fuel pump, a faulty camshaft will cause misfiring and can lead to increased emissions.
Under such conditions, the check engine light will flash or the engine computer may issue some trouble codes. At this point, the engine needs to be inspected to pinpoint the underlying cause. A broken camshaft will not only ruin engine performance but will also cause damage to the cylinder head, valves, pistons, and other parts of the engine, if left unchecked.
It is highly advised that you replace the camshaft instead of attempting any kind of repair. To prevent wear or damage on the camshaft, routine engine maintenance is the key. Make sure that you change the motor oil regularly and that you use high-quality oil as recommended by the manufacturer.
How can you find the right camshaft replacement?
Camshafts may all look the same but they vary in terms of shaft length and the number of lobes attached to the rod. You have to consider the valvetrain layout and cylinder arrangement of your engine to find out what type of camshaft you should install on your vehicle.
Your vehicle owner’s manual will be a good reference for the camshaft specs and engine design, whether the vehicle is equipped with an SOHC engine with one cam per head or a DOHC engine with two cams per head. You can also just shop for a camshaft replacement and other parts according to your vehicle’s year, make, model, and other details such as the trim level.
Quick Tips on Getting a New Camshaft
Your camshaft, sometimes called the "brains" of your engine, manipulates the valves that allow fuel and air into your engine. Your vehicle simply won't function without it, and the kind of camshaft you get determines engine qualities ranging from how much power and performance you can get to how well your engine idles. Picking out the right camshaft can be quite complicated. If you're looking to replace your camshaft with something other than the exactly the same type you started out with, here are some things you need to know:
Camshafts are usually made out of either of two types of material: chilled iron castings or billet steel.
- Chilled iron castings - This is the most common type. The chilling process makes the material harder. That, and elements added to the iron used, make for very durable camshafts for most driving applications.
- Billet steel - This is used only for very high-quality camshafts. A special heat-treating process called gas nitriding is used to make the steel extremely hard. This type of camshaft is much more expensive and is used for high-performance engines.
There are four basic types of camshafts. The type is determined by whether it's a roller camshaft or a flat tappet camshaft, and whether each type uses a hydraulic or a solid lifter.
- Flat tappet camshafts - These use a lifter with a slightly curved bottom sliding against the cam lobes. The curved bottom helps reduce friction. Flat tappet camshafts were in almost every V8 engine produced the late 1980s. They are still quite common and are relatively much cheaper.
- Roller camshafts - With a roller or wheel rolling over the cam lobes, the amount of friction and wear is greatly reduced in these camshafts. Roller camshafts provide better performance by allowing for more mid- to top-end power without compromising bottom-end power. These are much more expensive than flat tappet camshafts.
- Hydraulic lifters - These automatically adjust the valve lash (the distance between the valve stem and rocker arm tip) as needed. They are quieter, require almost no maintenance, and cause much less wear on the valvetrain. The only problem is how they may overfill with oil, causing the valves to stay open too long at high rpm. This can lean to engine damage at high speeds.
- Solid lifters - These are more ideal for racing since they don't have the oil-overfill problem of hydraulic lifters. However, they are also noisier and require periodic adjustment of the valve lash.
Other things to consider:
- As always, your vehicle's owner manual is a good place to start looking for information regarding any parts you plan to get for your vehicle.
- Your replacement camshaft must be compatible with your engine's cylinder head. Know the exact specifications of your cylinder head (make, model, size of intake/exhaust valves, etc.) and see if the camshaft you're getting can work with them.
Serious Engine Surgery: Replacing Your Camshaft
Your camshaft keeps your car running by manipulating the valves that allow fuel into your engine. This is a vital component as your vehicle simply won't run without it. Should your camshaft get damaged, you will have no choice but to replace it right away. You can save yourself some money by replacing the part yourself, but this is a job for an experienced DIYer and may take anywhere between four to six hours. Time to put those mechanical tinkering skills to the test!
Difficulty Level: Hard
Here's what you'll need:
- Wrench and socket set
- Torque wrench
- Razor blade
- Wire scrubber
- Clean rag
- Replacement camshaft
- New cover seal (this may come with your new camshaft)
- Lubricating fluid
- Personal protective equipment (safety gloves and glasses, closed-toe shoes, etc.)
- Vehicle owner manual
And here are the steps:
- Open the hood of your vehicle and use your wrench to disconnect the negative battery cable from the battery terminal.
- Remove the bolts that are keeping your air cleaner assembly in place and loosen the claps holding the intake pipe to the air box.
- Remove the entire air cleaner assembly.
- Locate the crankcase ventilation tubes and disconnect them from the camshaft cover.
- Remove any wires and brackets you may find on the camshaft cover. Use your socket wrench to remove any bolts.
- Use your socket wrench to remove the bolts securing the upper timing belt cover in place before removing the timing belt cover.
- Remove any crown nuts, grommets, and washers holding the camshaft cover in place. Don't lose any of them as you will use them again later.
- Lift the camshaft cover up and off the engine.
- Remove the gasket. If it has melded onto the cover and cylinder mating surfaces, use your razor blade and wire scrubber to remove the gasket material. Wipe the surfaces clean with the rag.
- Unbolt the distributor's mounting brackets and disconnect all electrical connections. Remove the distributor.
- Loosen the valve adjustment lock nuts until they no longer hold the valves open.
- Carefully loosen the rocker arm shaft pedestal bolts by turning counterclockwise in 1/4 turns. Follow a crisscross pattern with each bolt. When the bolts are loose enough, lift the rocker assembly out of the engine.
- You can now lift the camshaft out of the engine.
- Apply lubricating fluid to the camshaft, the camshaft bearings, and the valve lifters.
- Install the new camshaft. Make sure the timing marks of the camshaft and crankshaft gears are aligned.
- Return the rocker assembly and camshaft cover (use a new one if provided). Use your torque wrench to tighten all the bolts according to the torque specifications provided by your vehicle owner manual.
- Put everything back together by following the reverse order of disassembly.