Are Spark Plugs Reverse Threaded?

Spark plugs are essential ignition system components in every gasoline-powered engine. They are often overlooked, but your gasoline vehicle will not start without them. In my career as an automotive mechanic and motorist writer, I have answered several questions, one of which is, are spark plugs reverse threaded?

This question may seem complex since different car manufacturers use different technologies to produce their cars. Nonetheless, I’ll answer this question in this article. I’ll explain how to remove spark plugs without breaking them and also answer other questions like are spark plug threads universal?

are spark plug threads universal

Which way do you unscrew a spark plug?

When removing spark plugs, you must follow the standard way of unscrewing any threaded component. Fit the plug spanner on the protruding end of the plug and carefully unscrew it by turning it counter-clockwise (left-hand side), and avoid cross-threading, as this can wear out the threads in the cylinder heads.

Once the spark plug is loosened, remove it by using a tool like a metal picker or spark plug socket. However, it is essential to note that too much force will wear out the hex edge of the plug are even break it. If the hex edge is worn out or the plug stuck, you’ll need a stuck spark plug removal tool to loosen it.

Are spark plugs lefty Loosey?

Spark plugs follow the standard tightening and loosening of threaded components, which means they are tightened clockwise (righty tighty) and loosened counter-clockwise (lefty loosey). Hence, when removing a spark plug, turn it counter-clockwise until the spark plug is completely loosened from the threads and can be removed by hand or with a tool like a metal picker or spark plug socket.

Are spark plugs reverse threaded

As a certified automotive mechanic and a car writer with over a decade of experience, I can say with certainty that spark plugs are not reverse-threaded. All spark plugs follow the standard right-hand thread, clockwise to tight and counter-clockwise to loose.

However, it’s crucial to be careful when removing and installing spark plugs to prevent breaking, cross-threading, or wearing out the hex edges. Always use the right plug spanner when removing and installing the plugs to avoid wearing out the edges. And always follow the standard right-hand threading when tightening or losing the plugs to prevent cross-threading.

If a spark plug won’t come out with a socket after loosening it, get a spark plug extractor and remove the plug from the hole.

Do spark plugs loosen counterclockwise?

Yes, spark plugs are loosened counterclockwise, which is the standard convention of loosening any threaded object. So, when losing spark plugs, you should turn it counterclockwise. In other words, you should turn it towards the left-hand side.

Avoid turning spark plugs to the right hand when trying to lose it because that could cross-thread the spark plug thread. Of course, I know you won’t want that to happen.

If spark plugs are stuck, get one of the best penetrating oil for spark plugs and pour it into the hole. This will weaken the rust or anything sticking the plugs in the hole. Pouring a WD40 on stuck spark plugs will also do the trick.

are spark plugs left hand thread

Why can’t I pull my spark plugs out?

There are several reasons for a spark plug to get stuck in the hole and won’t come out. These reasons include;


The spark plug electrode can become corroded, especially if oil leaks into the spark plug hole. If the electrode is corroded, you’ll find it challenging to loosen the spark plugs and remove them from the hole. Plus, an engine with a corroded spark plug will stall or may not start at all.

Cross threading

If the person that installed the spark plugs the last time did not align them properly before tightening them, he might cross-threaded them. Cross-threading a spark plug simply means damaging the spark plug threads, making it difficult to loosen them. In most cross-threading cases, the plug will be turning as you try to loosen them but will not get loose.

Rust or carbon deposit

Carbon deposits can build up on the plug threads and make it challenging to loosen the plugs. Also, rust can accumulate on the spark plug holes, making it difficult to come off. Over time, these rust and deposits will form a bond and stick to the spark plug.

Rising temperature

The spark plugs and the cylinder head are made of different materials. Hence, they do not expand at the same rate. If the engine temperature rises due to overheating, the aluminum cylinder head will expand more than the plug material. If you try to lose the plugs while still in this state, they will become stuck with the cylinder head.

Oil in the spark plug hole

If oil drips into the spark plug hole, it’ll cause oil-fouled spark plugs. Over time, the oil will harden and stick the spark plugs in the hole.

Bad ignition coil

A bad ignition coil can cause a high electrical voltage to build around the coil, which can cause it to stick to the plug threads.

In any case, if you are experiencing difficulty in loosening a spark plug, do not force it, and do not think it is a reverse thread. Forcing it could cause damage to the engine or the spark plugs. Instead, ensure you use the right tool, add penetrating oil, and use a breaker bar.

Which socket is used to lose the spark plug?

Spark plug threads are not universal; hence, different plug sockets are used to remove spark plugs. In today’s vehicles, the majority of spark plugs use 16mm or 5/8” sockets. Some Asian and European cars use 14mm, some Fords use 9/16, and some other applications 13/16″, 7/8″, ¾”, or 18mm plug sockets.

Most spark plug sockets have a rubber foam or magnet that grips the spark plug as you grab it from the plug hole. If you are using an ordinary socket or your plug socket does not have a magnet or rubber grip, then you should get a metal picker for easy plug removal after losing it.

Final Words

To be precise, spark plugs are not reverse threaded. All spark plugs have the standard right-hand thread, meaning when tightening them, you turn them clockwise and counterclockwise when loosening them.

Remember, do not overtighten spark plugs to avoid cross-threading them and so you can easily lose them when you want to clean or replace them. And when losing, do not force a stuck plug. Instead, use the right socket and apply penetrating oil to any stuck plug.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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