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Excess engine noise is due to excessive clearance between two metal parts that should have little to no clearance. This clearance can be due to several things from a broken valve spring to a valve lifter sticking. Identify where the engine noise is being generated, with the engine running try to isolate where the noise is coming from in the engine, either the upper half, lower half, front half or rear half. Listen from above the engine or below the engine as this will help determine where to start looking for the cause of the noise.
Tapping Noise (lower and upper engine noise) - Check the engine oil level, your engine depends on clean engine oil to lubricate the internal moving parts, if the engine oil level is low or the oil is dirty it can cause internal engine parts to malfunction. For example: a valve lifter is responsible for holding valve train clearance to a minimum, if the oil level is low or dirty it can cause the lifter to malfunction which will allow excess valve train clearance creating engine tapping or clicking noise. In extreme cases or when your engine has run out or close to out it can cause one of the many bearing surfaces to fail causing permanent engine damage and noise until repairs have been made. If this condition is left unattended the engine will suffer permanent damage and fail. If your engine is making a noise change the engine oil and filter with the manufacturers recommended weight (viscosity) oil first, if that does not make a difference engine repair work is needed.
Knocking Sound (upper engine noise) - If you hear a lighter tapping noise from the upper half of the engine, shut the engine off and remove the valve covers. A camshaft is commonly used to operate poppet valves in a piston engine. A cylindrical rod is situated in the cylinder block or cylinder head that has oblong lobes or cams which push open the intake and exhaust valves. This force is applied on the valve directly or through an intermediate mechanism such as a rocker arm, lifter (cam follower) and push rods that are used to press against the valve for movement. Each valve utilizes a spring that will return the valve to its original position (closed) after the force is removed. If a valve spring has broken or a cam lobe is worn down it will cause the engine to create a tapping or clicking sound. To test for this condition, remove the ignition coil connector, ignition system or fuel pump fuse to disable power to the ignition or fuel system. Remove the valve covers to gain access to visually inspect the valve train. Have a helper crank the engine over while you watch the rocker arms or cam lobes, make sure they are all going up and down the same amount, if one or more lobes are traveling less than the others you might have a flattened cam lob and the camshaft needs to be replaced or a hydraulic lifter/follower (where applicable) that has collapsed and will need to be replaced. Also inspect the condition of the valve springs, use a flashlight and small mirror to aid in the inspection if needed. If a broken valve spring is discovered it will need to be replaced to correct the problem. And the final check, look at the height of the valve springs and retainers when in the closed position (pressure off) they should be exactly the same height. If one valve is higher or lower something is wrong with the cylinder head, valve or valve seat and needs to be repaired.
Rattling, Knocking Sound (lower engine noise) - If a heavier noise seems to be generated from the lower half of the engine the problem can be more serious and disassembly maybe required. But, sometimes a lower engine noise could be generated due to excessive carbon (carbon is a natural by-product of the combustion process) build up on top of the piston. This noise is created when carbon is compressed between the piston and the cylinder head. If you elect to perform a de-carbon procedure start and run the engine until warm, have a helper hold the engine at about 1500 RPM. As the engine is running poor a small amount of water down the throttle body, about a cup, you are creating a steam cleaning effect to break up the carbon that will exit the engine. Don't worry if steam is generated from the exhaust during the treatment, this is normal. If noise is gone after the treatment the carbon has been removed, if the engine noise is still there lower engine dis-assembly is required.
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