Torque Wrench for Spark Plugs? 7 commonly asked questions answered


There are varying opinions on the use of torque wrench for spark plugs the decision if up to you but know the risks and benefits before you hand tighten spark plugs . If you have ever snapped the head off of a bolt, then chances are you were applying way too much torque. Ensuring that a threaded component fits tightly is an important part of ensuring the proper maintenance of any vehicle. Although it would seem obvious that a threaded component such as a spark plug should be as tight as possible, over-tightening one can result in damage to the plug itself, or even to the cylinder head.

Do You Need a Torque Wrench to Change Spark Plugs?

Although it is not necessary to use a torque wrench in order to change a spark plug, it is highly recommended. While most modern-day cars feature an aluminum cylinder head, the threads on a spark plug are made of steel. Because the threads are made of steel, they are substantially stronger than the aluminum used in cylinder heads. As a result, over-tightening a spark plug can and often does result in the stripping of the threads in the cylinder head. The torque on spark plugs are usually around 13-15 ft. lbs they can easily be over torqued if you’re new to DIY repairs. It’s highly recommended to use torque wrench if you’re a newbie.

What Size Torque Wrench for Spark Plugs?

You can get torque wrenches in a number of different sizes. These sizes reflect the readily available rachet sets that can be purchased at any hardware store. As a general rule of thumb, when changing your spark plugs, you will use a 3/8-inch rachet. In fact, most standard rachet sets include at least one spark plug socket. Since the amount of torque that is needed to properly seat a spark plug within the cylinder head is between 5 and 7 ft. lbs., there is no need for anything larger than a 3/8-inch torque wrench.

What Type of Torque Wrench Do I Need for Spark Plugs?

There are a number of types of torque wrenches that you can purchase today. However, the clicking torque wrench is not appropriate for use on spark plugs. The clicking torque wrench is designed for higher foot pounds and is generally not sensitive enough for the smaller 5 to 7 ft. lbs. needed to seat a spark plug.

The beam-type torque wrench is considered to be the most affordable option for those who need to install spark plugs. They are sensitive enough to handle the lighter torque needed to properly seat a spark plug in the cylinder head, but can also be difficult to read. Because of the manner in which they are designed, there is also a lot of room for judgment errors in the amount of torque used.

There are also a number of electronic torque wrenches that are available today. Electronic torque wrenches are more sensitive and a lot easier to read.

What Happens If You Don’t Torque Your Spark Plugs?

Let’s face it, not everyone truly loves working on their vehicle. It is a time-consuming task, that often leaves your knuckles bruised and bloodied, not to mention covered with some nasty grease. People are in such a rush these days, that the simple things can be often overlooked. As spark plugs are such a crucial part of the operation of any internal combustion engine, it is important to make sure that they are functioning the best they can.

We’ve all heard stories about someone going to an oil change place, and having an inexperienced technician failing to properly tighten down the drain bolt. As a result, the oil begins to drain out of the bottom of the engine and the motor seizes up a couple of miles down the road. While failing to properly seat your spark plugs will not result in the engine oil spilling all over the city streets, it will result in lower compression ratios and the potential for fires.

An improperly seated spark plug allows air to be pushed out around the spark plug whenever the cylinder moves up to the top dead center position. This is an important point in the combustion process, and it requires a sealed compression chamber. Any leak, such as around the threads of a spark plug, can force fuel and air out of the cylinder resulting and damage to the engine, and possibly even a fire. It can also cause engine misfires and trigger check engine light.

How Do You Install a Spark Plug Without a Torque Wrench?

While it is not recommended to install a spark plug without using a torque wrench, it is still possible. There are times when you just don’t have access to a torque wrench in order to properly seat the spark plug. In order to determine how much torque, you are placing on the spark plug itself, you will need to calculate it based on the length of the rachet handle. It is much more difficult to determine the amount of torque being applied to the spark plug without using a torque wrench though.

Can You Tighten Spark Plugs Without a Torque Wrench?

Although it is possible to tighten spark plugs without using a torque wrench, it is hard to ensure that you are properly seating the spark plug in the cylinder head. Too little torque can result in a loss of compression, as well as pre-ignition. Too much torque can damage the spark plug or even the cylinder head itself.

When you fail to properly seat your spark plugs, the cylinder will fail to fire properly. This is a result of the fuel and air mixture being compressed by the cylinder as it moved to the top dead center position. It is during this compression, that the spark plug is supposed to ignite the mixture of fuel and air, forcing the piston back down. However, even a slight leak around the threads of the spark plug can reduce the amount of compression substantially.

When you over-tightening a spark plug, it is very easy to strip out the threads in the cylinder head. It is important to ensure that you never over-tighten your plugs because eventually, you will need to remove that spark plug again in the future. If you did not strip out the threads when tightening the spark plug, it is still possible to strip them out when you attempt to remove the spark plug from the cylinder head. This can create a lot of headaches for any vehicle owner.

How Tight Should A Spark Plug Be If You’re Hand Tightening?

Ultimately, it is still possible to hand tighten spark plugs safely. In order to hand tighten a spark plug, you will need to make sure that both the threads on the cylinder head and spark plug are free of any debris. From there, you can simply use your fingers to screw the spark plug into place until the compression washers contact the bottom of the spark plug well. You can also use the spark plug socket to help you with this task. Once you are no longer able to tighten the spark plug by hand further, you can use a standard 3/8-inch ratchet to finish the job, by turning the plug roughly a 1/4 of a turn further.

Decision is up to you to use a torque wrench or not, our recommendation is you do especially if this is you first time changing out spark plugs. Want to know what’s the best digital torque wrench? click here to find out.

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