How to Use an Automotive Torque Wrench to Change Spark Plugs

Any good mechanic knows that a strong spark is critical to keep an engine running strong and smooth. There are a lot of theories when it comes to tightening spark plugs, from “quarter turn past finger tight” to “stand on the wrench handle.” However, using an automotive torque wrench to properly install a spark plug is absolutely necessary to ensure that your engine doesn’t fail.

Under-tightening and Over-tightening Can Cause Serious Damage

Spark plugs thread into a hole in the engine’s combustion chamber. This chamber is subjected to thousands of powerful explosions every minute the engine is running. The spark plug hole is a path for combustion pressure, and therefore engine power, to leak out.

  1. Under-tightening: A spark plug that seems extremely tight using a socket wrench can be loose once it’s hot and under pressure.

A loose spark plug leaks power, saps fuel efficiency, and can cause harmful misfires. Using an automotive torque wrench to properly torque a spark plug ensures that it’s installed according to the specs provided by the engineers who designed the engine, ultimately preventing loosening.

  1.  Over-tightening: When a spark plug is overtightened, there’s a very real risk of breaking it off or stripping the threads.

 torque wrench“Snap” is one of the worst sounds a mechanic can hear. The sound of a connector breaking or threads stripping means damage has occurred, which can lead to unwanted time or money. A broken spark plug often requires specialized tools for removal. It needs to be drilled and tapped, then removed using reverse-threaded tools. This isn’t an easy or cheap fix, and it’s going to take time. And it’s the worst case scenario if a spark plug is overtightened to the point of failure.

On the other end of the spectrum, the threads in the cylinder head can strip out. When this happens, it’s often necessary to remove the head and have it drilled, filled, and tapped by a machine shop. That’s hours of time and hundreds of dollars wasted that can all be avoided through the use of proper tightening with an automotive torque wrench.

Steps on Using an Automotive Torque Wrench to Change Spark Plugs

When the time comes to change a spark plug with an automotive torque wrench, there are some basic steps to follow. These may vary slightly from one vehicle to the next, but it generally follows:

  1. Locate the spark plugs—You may have to remove engine covers, air ducts, or other parts to easily access the spark plugs. On some SUVs and trucks, it’s often easier to reach the spark plugs from a wheel well.
  2. Number the wires—Putting the wires back in the wrong order will cause a lot of problems. Use tape and a permanent marker to note which wires connect to which plugs.
  3. Remove the Wires—Pull on the boot connected directly to the spark plug. Never pull the wires themselves, as this is likely to damage the conductor. Use a firm pulling/twisting motion to free the boot from the plug.
  4. Pull the Plugs—Use a socket wrench and deep-well socket to remove the plugs from the cylinder head. Turn the plugs counter-clockwise until they’re free of the mounting hole.
  5. Take a Look—Examine the mounting hole for debris or corrosion. Use a plug cleaning brush to remove any debris from the threads.
  6. Seat the Plug—Use your finger to seat the plugs in the mounting holes and give a few clockwise turns to start threading them. They should thread smoothly and easily. If they don’t, make sure that the threads are clean and you’re not cross threading the plugs.
  7. Torque them Down—Using an automotive torque wrench and socket, tighten the spark plugs to the setting indicated by your owner’s or service manual.
  8. Reconnect—Push the wire boots firmly onto the spark plug connector. You should feel a slight “pop” when they are seated correctly.
  9. Test—Start the vehicle and listen for any rough idling or misfires. If there are any problems, recheck the connections.

Get it Tight, Get it Right

Too many mechanics think that torque wrenches are for large, complex automotive parts. Yet it’s the small, simple parts that can cripple your vehicle and cost you unwanted time and money. You should be using an automotive torque wrench on each and every part of your car that has a torque value assigned. That’s the best way to ensure that parts are installed correctly, and won’t fail under pressure.

Call us at 1-888-925-2763 or contact us to speak with a MountzPro representative to learn more about how to use one of MountzPro’s automotive torque wrenches to change your spark plugs


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