How Tight Do You Tighten Spark Plugs?

Spark plugs are vital for the performance of your automotive devices. These are used to deliver electric current from the ignition system to the combustion chamber of a SI (spark-ignition) engine to ignite the compressed mixture by a spark.

You need to tighten most spark plugs between 8 to 40 Nm, depending on the thread size. Following the manual-specified torque is a must for igniter installation. We recommend using a torque wrench to avoid under or over-tightening.

Since the igniter is an indispensable part of the engine, you have to double-check the torque settings prior to installation. Let’s see how much you need to tighten spark plugs.

What’S The Proper Way of Tightening The Spark Plugs?

• First, you have to get rid of all the dust and debris from the cylinder head, and then remove the thread from the plugs.
• Then start screwing the plug until the cylinder head reaches the gasket.

You can tighten the spark plug by using the torque wrench. It can also be done without the torque wrench. Both options are explained below.

Tightening with a Torque Wrench

A torque wrench is a special tool that is used to apply a specific torque to tighten something like a nut, plugs, and so on. The best way to tighten a spark plug is to use a torque wrench. The torque wrench will allow you to tighten the igniter precisely. Both over-torquing and under-torquing can cause the problem.

If your igniter has a recommended torque level in foot-pounds, then you need to have an ft-lb torque wrench. But in case you have an inch-pound torque wrench, you have to convert the unit while using it. We recommend having a similar type of torque wrench.

Tightening without a Torque Wrench

Even though it can be tough for beginners, you can try it out if you don’t have a torque wrench. The easiest alternative is to use a universal plug wrench to tighten the sparkers. But with this method, you have to be extra cautious with accuracy.

How much should you tighten the spark plugs? (Varied by Brands)

Every brand comes with unique specifications and recommendations for tightening the sparkers. Here are some brand-specific data below.

NGK Spark Plugs

Thread Diameter of Plugs

Tightening Torque

18 mm	35 – 40 N.m (3.5  – 4.0 kgm)
14 mm	25 – 30 N.m (2.5 – 3.0 kgm)
12 mm	15 – 20 N.m (1.5 – 2.0 kgm)
10 mm	10 – 12 N.m (1.0 – 1.2 kgm)
8 mm	8 – 10 N.m (0.8 – 1.0 kgm)

Denso Spark Plugs

Compatible Models	Thread Size	Recommended Torque	Recommended Tightening Angle for New Sparking Plugs	Recommended Tightening Angle for Used Sparking Plugs
All Types	M 8	8-10N･m	Around 1/3 turn	Around 1/12 turn
The rest than the types shown below	M10	10-15N･m	Around 1/3 turn	Around 1/12 turn
UFE, IUH, VUH, VNH Types	M10	10-15N･m	Around 2/3 turn	Around 1/12 turn
Stainless Gasket Type (*1)	M10	10-15N･m	Around 3/4 turn	Around 1/12 turn
All Types	M12	15-20N･m	Around 1/3 turn	Around 1/12 turn
The rest than the types shown below	M14	20-30N･m	Around 1/2 turn	Around 1/12 turn
Stainless Gasket Type (*2)	M14	20-30N･m	Around 2/3 turn	Around 1/12 turn
All Types	M18	30-40N･m	Around 1/4 turn	Around 1/12 turn
All Types	M14 Taper seat	10-20N･m	Around 1/16 turn	Around 1/16 turn

Champion Spark Plugs

Type &Part Number	Thread Size	Cast Iron Head*Recommended Torque with a Torque Wrench	Cast Iron Head*Recommended Torque without a Torque Wrench	Aluminum Iron Heads*Recommended Torque with a Torque Wrench	Aluminum Iron Heads*Recommended Torque without a Torque Wrench
Y678 (Gasket type)	10 MM	8 – 12 LB. FT.	¼ Turn	8 – 12 LB.FT.	¼ Turn
P678 (Gasket type)	12 MM	10 – 18 LB. FT.	¼ Turn	10 – 18 LB. FT.	¼ Turn
N678 (Gasket type)	14 MM	26 – 30 LB. FT.	½ to ⅝ Turn	18 – 22 LB. FT.	⅜ to ½ Turn
A678 (gasket type)	18 MM	32 – 38 LB.FT.	½ to ⅝ Turn	28 – 34 LB.FT	⅜ to ½ Turn
A478 (Gasket type)	⅞”	50 – 55 LB. FT.	½ to ⅝ Turn	–	–
Tapered Seat Type	14 MM	7 – 15 LB. FT.	1/16 Turn (Snug)	7 – 15 LB. FT.	1/16 Turn (Snug)
Tapered Seat Type	18 MM	15 – 20 LB. FT.	1/16 Turn (Snug)	15 – 20 LB. FT.	1/16 Turn (Snug)

E3 Spark Plugs

Type	Thread Diameter	Recommended Tightening Angle
Gasket	10 mm	1/2 turn
Gasket	12 mm	3/8 to 1/2 turn
Gasket	14 mm	1/2 to 3/4 turn
Tapered seat	–	1/16 turn

Autolite Spark Plugs

Type	Thread Diameter	Recommended tightening angle
Gasket	10 mm	1/4 turn
Gasket	12 mm	3/8 turn
Gasket	14 mm	1/2 turn
Gasket	18mm	1/2 turn
Tapered seat	–	1/16 turn

Bosch Spark Plugs

You should use a 1/4 turn if the spark plug comes with a gasket. And it’s better to use a 1/16 turn when the sparker has a tapered seat. Check the user manual provided by Bosch before installing them.

Pro Tips: “ You should avoid using any anti-seize lubricants on the spark plug threads. Because the lubricants may minimize the friction created by threads, therefore, it can lead to over-tightening.”

What happens if the spark plugs are too loose?

If the spark plugs of your car are not tightened properly, it will damage the engine in the long run. Loose sparkers can affect the overall performance of your car.

Here are Some of The Adverse Impacts of Loose Igniter Below:

Inconsistent Engine Performance: Loosely attached spark plugs will lead to trouble when starting the engine. It will also cause misfires and reduce the acceleration rate.

Harmful Detonation: The unstable combustion in the engine causes knocking or pinging. It may even cause permanent damage to the engine.

Overheating & Pre-Ignition: Owing to the loose sparkers, the engine may overheat and combust improperly. And these will lead to pre-ignition.

Dead-Cylinder & Piston Damage: The ignition coil can be weak due to the under-tightened spark plugs, and it will result in a cylinder misfiring. It can cause piston damage as well.

The above difficulties are the symptoms of the under-tightened sparkers of your car engine.

What Are The Effects of Over-tightened Spark Plugs?

The major effects of overtightened spark plugs are contingent misfiring, troublesome engine starts, alleviated RPMS, and many more. You will also face some issues such as difficulties while removing the igniter. And the electrode or insulator may break.