How Tight Should Spark Plugs Be? (Explained!)

Spark plugs need proper tightening so they can perform at their best. However, if you overtighten or under tighten it, it can lead to issues that can damage your engine or affect performance. With this in mind, you may wonder about how tight you need your spark plugs to be. Thus, you may ask:

How tight should spark plugs be? The tightening of spark plugs varies on your engine and the spark plugs you have. However, please take it as a rule of thumb to finger-tight your spark plug until its gasket touches the cylinder head. Afterward, it would be best if you tightened it for around a half or two-thirds turn more with a spark plug wrench.

Since spark plugs play an essential role in an engine’s performance, you must always be mindful of how you install them. Moreover, whenever you do so, make sure it’s appropriately tightened so you can get the best out of it and at the same time avoid problems caused by improper tightening.

In this article, you’ll see our in-depth take on spark plugs and how important it is to tighten them all the time properly. This way, you can understand the risks if you overtighten it or under tighten it. It will also help you on how you can achieve proper tightening for your spark plugs.

Without further ado, let’s get into it!

Table of Contents

What Is the Proper Torque for Spark Plugs?

Spark plugs come in various types and angles. Thus, the proper torque for them depends on such variations. In most cases, the proper or recommended torque varies on the size of the spark plug threads.

Here’s a table with different thread sizes and their respective recommended torque. It also includes the recommended tightening angle and the applicable models.

Thread Size	RecommendedTorque	New Plug	Previously Used
M 8	8-10N･m	About 1/3 turn	About 1/12 turn
M10	10-15N･m	About 1/3 turn	About 1/12 turn
M10	10-15N･m	About 2/3 turn	About 1/12 turn
M10	10-15N･m	About 3/4 turn	About 1/12 turn
M12	15-20N･m	About 1/3 turn	About 1/12 turn
M14	20-30N･m	About 1/2 turn	About 1/12 turn
M14	20-30N･m	About 2/3 turn	About 1/12 turn
M18	30-40N･m	About 1/4 turn	About 1/12 turn
M14Taper seat	10-20N･m	About 1/16 turn	About 1/16 turn
M14（Gas）	20N・m	–	–
M14（Gas）	17.5N・m	–	–
M18（Gas）	30N・m	–	–

Can You Over-Tighten Spark Plugs?

Yes, you can overtighten a spark plug. Since it attaches to the engine, you can always turn it a little more or have it loosely attached.

The risks to these problems can cause damages to the metal shell. In addition, such pressure can also damage the spark plug threads, eventually leading to breakage.

Aside from the thread damage, an overtightened spark plug can also damage the internal gas seal, causing a fracture in your engine’s insulator.

In general, anything that affects the torque can lead to a failing plug or even engine damage. Thus, it’s essential to keep it in mind while you tighten your spark plugs.

How Do I Know If My Spark Plugs Are Too Tight?

You’ll know that your spark plugs are too tight when you notice the symptoms or effects of overtightening. If you want to make sure that your spark plugs are correctly tightened, consider checking if you experience these issues with your engine.

Poor Engine Performance

Poor engine performance can mean many things. However, one of the leading causes of such is the failing spark plug. When you overtighten your spark plugs, it can affect the functions it offers. Thus, it can lead to poor engine performance.

If you recently adjust your spark plugs and start noticing the engine performance decreased, it would be best to recheck the tightening.

Engine Misfires

A misfiring engine is also a sign of a worn-out and failing spark plug. However, if your spark plug is newly replaced, it can also mean that you overtightened it.

Trouble getting the engine to start.

If you find it challenging to start your engine after replacing or fixing your spark plug, it may mean you overtightened it. An overtightened spark plug is likely to fail due to the pressure build-up in the gasket. As a result, it affects your engine startup.

Slow, difficult acceleration

Spark plugs also play an essential role in the acceleration of your engine. Thus, you can notice a failing or overtightened spark plugs can lead to a slow and rough acceleration.

Now, since overtightening of spark plugs can cause many problems, you may wonder what would happen if you don’t tighten it enough.

What Happens if Spark Plugs Aren’t Tight Enough?

In general, a loose spark plug can cause more issues than an overtightened one. For instance, a loose spark plug will create the hole and likely damage the threads while pushing their way out.

Thus, if your spark plug is a cross-threaded one, it will likely damage the plug and the threads in your plug’s head.

In most cases, you’ll need a reamer thread tool with such a kind of issue. With this tool, you can repair the threads and tighten the plug afterward.

However, if you try to start your car with a loose spark plug, it will be challenging to do as the spark plug won’t create enough power to start your engine.

How Do I Know If My Spark Plugs Are Too Loose?

If your spark plugs are too loose, they will only continue to loosen further until it causes a whole load of problems. It will eventually cause damage when you continue driving with a loose spark plug.

In most cases, the loose spark plugs will only affect the performance of the cylinders. However, it doesn’t work, especially if you would look at it as a half-plugged appliance.

Now, if your plugs are too loose, your engine is highly likely to experience one of the following:

Problems with engine performance
Poor Engine Performance
Detonation
Pre-ignition
Dead cylinder

If you have one or more improperly tightened spark plugs, you can experience issues such as:

Engine Pre-Ignition
Trouble getting the engine to start
Misfires
Slow, difficult acceleration

A loose spark plug can cause significant overheating. If such an issue happens, it will eventually lead to abnormal or poor combustion.

Should You Put Anti-Seize on Spark Plugs?

An anti-seize is a product that acts as a lubricant. Thus, if you use it on spark plugs, it can affect the performance of the torque. In short, you shouldn’t put anti-seize on spark plugs as it can only cause harm.

In general, an anti-seize is enough to increase the torque values. However, with such an increase, you also create more risks to the spark plug.

The increase in torque value can lead to a spark plug thread breakage. Or it can also induce a stretch on the metal shell.

If you own or use an NGK spark plug, it would be best to avoid using or applying an anti-seize in it. Now, if you want to put anti-seize on spark plugs, you need to be mindful of where to put it.

Where Do You Put Anti-Seize on Spark Plugs?

If you don’t know where to put anti-seize, you have to be mindful of the places to avoid. In general, you only need to put this product on the middle threads.

As much as possible, you must avoid putting anti-seize on the first thread, on the spark plug ground, and its electrode.

In general, here are a couple of things you need to follow whenever you’re putting anti-seize on spark plugs:

Apply small amounts only. A tiny amount goes a long way.
When putting it to Spark Plugs, use it sparingly
Apply it only on the middle threads.
Only put this item to the middle threads of the plug.
Avoid putting it on the first thread.
Avoid putting it on the ground and electrode.
Be careful in torquing your spark plugs.

If you’re not sure how to do this stuff, then try to get an expert or someone who knows to do it for you. This way, you can be sure you place anti-seize correctly and avoid improper tightening of your spark plugs.

Summary

In a nutshell, you should only tighten a spark plug for around a half or two-thirds tighter after you finger-tight it. The way you tighten spark plugs depends on your engine and the spark plugs you’re using.

As a rule of thumb, finger-tighten your spark plug until the gasket makes contact with the cylinder head. After that, using a spark plug wrench, tighten it for another half or two-thirds turn.

Also Read:

Resources

Image credits – Canva