What is engine knocking? How does it sounds? This article is to help you to identify knocking sounds on your engine which is dangerous and need to be fixed as soon as possible. According to latest issue, the change of petrol usage from RON97 to RON95 which will affect the performance of your engine, if you found that your engine is knocking with the “tack tack tack” sound repeatedly like video below, it is a sign that you cannot use the RON95 and must immediately change back to RON97. RON number is the minimum octane number to prevent from engine knocking. Here we share some definition of engine knocking.

 
Engine knocking refers to the metallic sound an engine can produce when pressure is applied to the gas pedal. The noise may be a hollow knocking sound or it can be more of a rattling-type sound—in either case, it’s not a sound you want to hear.

When an engine knocks, it releases pollution into the environment in the form of nitrogen oxide (NOx) and raw, unburned hydrocarbons (HCs). These two chemicals are poisonous gases that show up as yellowish-brownish in a polluted sky. They can also cause respiratory problems like asthma and emphysema—a knocking engine is never a good thing.

Knocking (also called knock, detonation, spark knock or pinging) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise time in the piston’s stroke cycle. The peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic “pinging” sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive. It should not be confused with pre-ignition (or preignition), as they are two separate events.

Other Cause of engine knocking are:

+Defective main crankshaft bearings

 
+A cracked or broken flywheel or flex-plate that attaches the engine to the transmission
+A worn water pump bearing
+A failed or loose timing belt tensioner can knock when the timing belt slaps against it 
+An air conditioning compressor can knock when it is failing or icing up

+An alternator with worn rotor bearings can knock when the pistons fire

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