Updated at: 01-07-2022 - By: Lucas

The performance of a car depends on the spark plugs. They send the spark that lights the fuel and air mixture in the combustion chamber on fire. The performance of the engine depends on how well the spark plug is put in.

Most spark plugs are tightened between 8 and 40 Nm. To avoid over- or under-tightening, a torque wrench should be used to set the torque to what the manufacturer says. The spark plug usually needs more tightening if the thread size is bigger.

Because spark plugs are so important to how an engine works, it’s important to double-check the torque settings before you install them. Let’s look at how to install spark plugs and what happens when they are too loose or too tight.

Can You Over-Tighten Spark Plugs?

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It’s not a good idea to tighten spark plugs too much. The extra torque puts stress on the metal shell, which can break the threads in the cylinder head, spark plug, or insulator.

When installing spark plugs, it’s important to follow the instructions from the manufacturer.

Too much torque damages the threads on both the spark plug and the cylinder head.

It also puts stress on the spark plug’s inner seal or causes a tiny crack in the insulator.

Symptoms of Over-Tightened Spark Plugs

Over-tightened spark plugs can cause misfires that are hard to predict, lower RPMs, and hard engine starts. Also, you will find that:

Overly tight spark plugs are hard to remove

If the spark plug is screwed in too tight, it is hard, if not impossible, to loosen it.

The spark plug is stuck to the cylinder head by rust, deposits, and dirt that have built up over time.

Loose Objects can get in Combustion Chamber

Breaking of the spark plug electrode or insulator is another thing that could happen.

These pieces can get into the combustion chamber, where they can damage the surfaces they touch.

What Happens When Spark Plugs Are Too Tight or Loose?

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1. Loose Spark Plugs

Loose spark plugs hurt the engine’s performance as a whole and cause damage over time. Both rubber and hydro-elastic engine mounts should be able to stop the vibrations inside the engine.

If the spark plugs aren’t tight, these vibrations can’t be taken in. As time goes on, the plugs open up more, which changes how well the cylinder works.

If there isn’t enough torque, the spark plug won’t be in the right place on the cylinder head. There isn’t enough contact with the cylinder head, which makes it hard for heat to travel.

During the downward stroke, there isn’t much compression inside the cylinder, so oxygen can get in through the loose plug. When there is too much oxygen and not enough condensation, the engine loses power and misfires.

Other issues that may arise are:

Poor Engine Performance

When one or all of the spark plugs aren’t attached well to the cylinder heads, it can make it hard to start the engine, slow it down, or cause it to misfire.

Engine Pre-Ignition

A loose spark plug can cause the engine to get too hot and not burn properly. If this happens, the surface will be too hot, which will cause pre-ignition.

Harmful Detonation

Detonation is when the engine’s fuel and air mix together in a way that is hard to predict. This can be heard as knocking or pinging. It causes the engine to break down completely or get hurt for good.

Dead Cylinder and Piston Damage

When a spark plug is not tight enough, it can fall out completely, leaving a dead cylinder as the car moves.

2. Tight Spark Plugs

When you try to take out a spark plug that is stuck, you can damage the bolt hole. The bolt hole in the cylinder head should always stay in good shape.

If the spark plug is broken, misshapen, or stripped, you won’t be able to put in a new one. You end up having to pay even more to fix it.

Stripped Threads

When a spark plug is tightened too much, the metal shell tends to stretch. Because of this, the threads break or split. It can also break the insulator or the gas seals on the inside.

Also, there is less heat loss, which can lead to pre-ignition and engine damage.

When the threads get stripped, the spark plug won’t tighten, so it keeps turning. The only way to fix it is to replace the head or fix the Helicoil, both of which are expensive.

If you tighten a spark plug too much, you will need a new one because the compression in the gasket only works once.

How to Know If Your Spark Plugs Are Too Tight

The best way to check how tight something is is to look at the spark plugs.

When they are too loose, we can turn them by hand.

Even with a wrench, you can’t turn them if they are too tight.

How Tight Should I Tighten My Spark Plugs?

We can use our hands to get the spark plugs with tapered seats as tight as we can with our fingers.

Next, use a spark plug wrench to turn the plug another 1/16 of a turn, as instructed by the manufacturer for a 14mm thread.

Even better, get a torque wrench to make sure you’re tightening them to the right amount.

What’s the Proper Tightening Procedure?

The first step is to clean the cylinder head and the spark plug threads to get rid of dirt and dust.

The next step is to screw in the spark plug until the head of the cylinder touches the gasket.

Tightening With a Torque Wrench

Different manufacturers of spark plugs have different torque requirements. You can find this information online.

We have to look for more information about the specs.

Tightening Without a Torque Wrench

If we don’t have a torque wrench, we can screw in the spark plug by hand and then tighten it with a plug wrench.

Some of the specs from the manufacturer are:

Autolite Spark Plugs

If there is a gasket on the spark plug, use;

1/4 turn for 10mm plugs

3/8 turn for 12mm plugs

Both 14mm and 18mm plugs need 1/2 turn.

If the seat is not flat, use 1/16 turn.

Bosch Spark Plugs

Use a 1/4 turn if the spark plug has a gasket and a 1/16 turn if the seat is tapered.

Champion Spark Plugs

Use a 3/8 to 5/8 turn for spark plugs with a gasket. Use a 1/16 turn for seats that are tapered.

Champion Spark Plugs

Use a 1/4 to 1/2 turn if the plug has a gasket.

If the seat is not flat, use a 1/8 turn.

E3 Spark Plug

Use for spark plugs with a gasket;

1/2 turn for 10mm plugs

12mm plugs need 3/8 to 1/2 turn

1/2 to 3/4 of a turn for 14mm plugs

Use a 1/16 turn for plugs with a tapered seat.

NGK Spark Plugs

If the plug has a seal, turn it between 1/2 and 2/3 of the way.

Use a 1/12 to 1/8 turn if the seat is tapered.

Whenever a mechanic instals a spark plug, he or she should use the right torque wrench to match the torque on the spark plug package.

If the spark plugs are too tight or too loose, oil could leak out of their cases. The oil could get hot and start a fire while we are driving, or it could damage other parts of the engine.

Frequently Asked Questions (FAQs)

Can I Use Anti-Seize on Spark Plugs?

Don’t use anti-seize lubricants on the threads if you can help it. Lubricants reduce the friction caused by threads, which makes it easier to overtighten.

Can I Change My Spark Plugs?

You can change the spark plugs on your own if you know how they work. Keep in mind that even small mistakes during installation can hurt your engine in big ways.