What Happens If You Over Tighten A Spark Plug? [Answered By Mechanic]

Spark plugs are installed or threaded in the cylinder head alongside the intake and exhaust valves. 

If you have over-tightened a spark plug, it can:

  • Damage to the cylinder head and the thread of the spark plug
  • Foreign objects or the pieces from the damaged cylinder can fall into the combustion chamber
  • The spark plugs would be difficult to untighten or remove from the cylinder head

Such an over-tightened spark plug damages the cylinder head, and the thread of the spark plug can lead you to fix or find replacements for these parts.

Fuel Combustion On Your Car Engine

YouTube video

When you burn fuel on your car’s internal combustion engine, the fuel combines with air and passes to an intake valve going to the cylinder.

As the air-fuel mixture moves down the cylinder, the piston will compress this mixture, and then the spark plug will ignite it. 

The ignited or combusted air-fuel mixture will expand and push the piston downward. 

As the connecting rod from the crankshaft to the piston will try to complete its rotation clockwise, the piston will move upward. The piston will push the burner air-fuel mixture to be released into the exhaust valve. 

When the piston reaches the top part of the cylinder near the valves, the intake will release the new set of air-fuel mixture to repeat the four-stroke cycle of the internal combustion engine. 

The four-stroke cycle, as it is called because of the number of strokes made to burn fuel, which is consists of:

  • 1st stroke: intake stroke
  • 2nd stroke: compression stroke
  • 3rd stroke: combustion stroke
  • 4th stroke: exhaust stroke
Read More:  How To Tell If Your Car Is Bugged

Two strokes of the piston (upward and downward) consist of one revolution of the crankshaft.

The crankshaft is measured through revolutions per minute (rpm) or the number of rotations it makes in a minute. At 5,000 rpm, the crankshaft consists of 83 rotations per second.

Frequently Asked Questions

What Is A Cylinder Head?

The cylinder head is part of the internal combustion engine working with the other parts to burn the fuel in your car. 

It is mounted on the cylinder block, which functions as a support structure for the engine cylinder. It is made of aluminum metal covering the top part of the cylinder or the chamber for burning the fuel. 

Cylinder head functions as follows:

  • Provide a mounting structure for the components in the upper part of the cylinder, such as the intake and exhaust valve, injectors, spark plugs and camshafts that activate the intake and exhaust valves
  • Contains the passage for coolant, oil, and combustion gasses
  • Disperses the heat of the engine

What If The Spark Plug Is Loose?

If the spark plug gets loosened or is tightened loosely, your car can have poor engine performance, detonation, and dead cylinder.

Poor Engine Performance

Spark plugs that are not tightly screwed into the cylinder head can make misfires, slow acceleration, and slower to start the engine.


Due to loose spark plugs, detonation, which refers to the spontaneous combustion inside the engine, can encourage pre-ignition or early ignition of a spark plug before the air-fuel mixture can even be compressed. 

The pre-ignition is due to the spark plug’s contact with the hot surface. Such detonation can lead to engine damage for unsynchronised functions of these components.

Read More:  Can You Drive With A Bad MAF (Mass Airflow) Sensor [Symptoms & Diagnosis]

Dead Cylinder

The loose spark plugs could pop out, with nothing to ignite the air-fuel mixture. A cylinder with an air-fuel mixture not combusted can decrease and eventually lose the engine power.

 You may notice a cylinder not working if it has also increased its vibrations.

How To Change and Install Spark Plugs?

Here is the step-by-step of a safe installation of spark plugs into the head cylinder:

  1. Park your car on a flat, dry surface and keep the car engine cool.
  2. Remove the spark plug wire end and its metal terminal inside.
  3. Remove the Coil On Plug (COP), starting with disconnecting the electrical connector from the ignition coil.
  4. Unscrew the spark plug using the spark plug socket.
  5. Inspect the new spark plug to be installed if the plug part number matches the part number and box description.
  6. Install the new spark plug with proper torque to tighten it well.

Leave a Comment