Reasons for Engine Knock

Knock knock. Who’s there? That’s your engine, and it’s making a sound you’ve never heard before. It may sound like a metallic ping, or a tick, and that’s what is known as engine knock. If you hear often, you have a big problem. The goal is to prevent it at all costs. If you’re not sure why you have it, nor how to prevent it, we’ll discuss the three most common reasons and what you can do about it.

What Does it Really Sound Like?

One person may say that engine knocking doesn’t really sound like knocking. It’s more of a pinging sound. Others may think it’s more like a tick than a ping. Whatever you think it sounds like, just remember that it’s bad for your engine. Engine knocking, pinging, or ticking is most likely pre-ignition of the fuel and air mixture inside your engine cylinders. It usually happens when you’re accelerating from low-speed, high-torque conditions that require the most power output from your engine. It’s unlikely to occur just cruising at steady speed traveling down the road.

Why Does Engine Knock Occur?

The term engine knock may be a little misleading. Two conditions commonly referred to as knock are: pre-ignition and detonation. They are effectively the same condition, but they have different causes. Attempting to fix the wrong cause will lead you in circles, so defining the root cause of the problem is your first order.

If your engine is running properly, your spark plug will fire a few degrees before the piston reaches top-dead-center (TDC). This timing will ignite the air and fuel mixture in your engine cylinder and force the piston down as the gas combustion expands. If done at the correct point in the piston movement, your engine will make maximum power with optimal efficiency.

A condition called pre-ignition occurs when the fuel and air mixture ignites before it is supposed to. That early ignition causes a loss of power and can cause damage to the engine components. It is often caused by low-octane fuel or deposits on the top of the piston surface. Your vehicle has a minimum octane rating, and using fuel with lower octane can cause pre-ignition to occur. Carbon deposits on the piston can heat up in the ignition cycle and later cause the fuel/air mixture to ignite prematurely.

Detonation is a similar problem of ignition at the wrong time of the piston stroke. It occurs after the plug has fired, but it has the same effect on the engine. Thankfully modern computerized engines have sensors that can detect engine knock conditions and adjust the engine spark timing to counteract the problem. It can save your engine from being damaged, but it also robs your engine of power and torque. If you suddenly lose efficiency and performance, your engine may have detected engine knock.

Does Your Engine Have a Tick Tick Sound?

You may hear other noises from your engine that don’t sound like a knocking sound. What if it sounds more like a ticking sound from the top of your engine? If that’s the case, you may have an oil starvation issue with your valves and rocker arms.

When you start your engine, especially when left overnight, the valvetrain in your engine won’t have oil. Gravity drains your oil down to the bottom of the engine and into the oil pan.  When you start the engine it takes a moment for the oil to re-coat the inside of your engine.  Most engines use a hydraulic lifter in the valvetrain that have an oil-assisted plunger and spring to compensate for valve lash. This type of lifter helps the engine to run smoother and more quietly. Without the oil it will sound like a ticking coming from your engine, but it should go away when oil pressure builds in the engine and the valves are pressurized with oil.

Is Rod Knock Different Than Engine Knock?

Your engine is a finely tuned machine, and it has very tight clearances between components. Engine oil is made to fill all small clearances and prevent metal-to-metal contact from occurring. Using poor quality oil can allow that thin barrier of oil to fail and allow metal components to touch. That touching condition may sound like a knock. Over time, the metal-to-metal contact will cause extreme wear on each metal surface. When that occurs on spinning components, like connecting rods and the crankshaft, they will make more and more noise as the parts wear out quickly.

How Do I Prevent Pre-Ignition and Detonation?

Preventing pre-ignition and detonation may be an easy fix. If you are using low octane gasoline, you may need to increase the octane level by buying higher octane gasoline at the pump. If octane isn’t your problem, you may have deposits in your engine cylinders. Those can be cleaned with a good fuel system cleaner like AMSOIL P.i. Performance Improver Gasoline Additive.

How Do I Prevent Oil Starvation and Rod Knock?

Oil starvation may occur because of deposits blocking oil passages inside the engine, or poor-quality oil having a high cold pour point. If you have deposits in your oil, you may find that using a higher quality oil with superior detergents can clean out deposits.

AMSOIL products have more detergents than most competitors and will remove deposits that can slow down oil flow. AMSOIL engine oils also have a very low temperature pour point, which allows them to flow better at cold temperatures. They prevent oil starvation at low temperatures, where other oils won’t. You may also find that adding AMSOIL Upper Cylinder Lubricant can help valvetrain components like lifters and rocker arms quiet down.

Your engine should run smoothly without making too much noise. If you hear it knocking, pinging, or ticking, something is definitely wrong. You may find a sensor on a newer engine has gone bad, or a simple change to better oil or adding a fuel system cleaner with octane booster can remedy the problem. No matter what viscosity your engine requires, AMSOIL will have you covered. Today’s synthetic engine oils reduce thermal runaway, prevent corrosion, and keep your engine clean. If you need help with determining a complete maintenance plan for your vehicle, your local AMSOIL dealer at Buy Great Oil is here to help with a complete package of products and hints to make the job easier and more cost effective.