Tightening torques for spark plugs

When forces act through a lever on a fulcrum one speaks of torque.

This also applies to spark plug installation. Here, however, it is called a tightening torque. This describes how tight a screw is fastened.

In this conjunction a tightening torque is selected which will ensure that the connection will not become loose under any operating conditions.

It is important, therefore, to pay attention to the tightening torques and installation instructions when exchanging the spark plugs. These are given in detail in the main NGK catalogue. It is known from experience that though rarely much of the occurring temperature and vibration damage is caused by incorrect tightening torque, i.e. incorrect installation. Modern engines in particular react very sensitively in this respect.

When the tightening torque is too low, there is a danger of compression loss, loosening of the center electrode, and temperature damage due to reduced heat dissipation. It can also happen that the spark plug works itself loose. When tightening torque is too high, the cylinder head may become damaged. In addition, too high forces acting on the spark plug can cause damage to the thread.

The tightening torque can also be determined later by measuring the height (thickness) of the sealing ring. A spark plug has been installed with a non-compressed sealing ring with too low a torque. Vice versa has a spark plug with a sealing ring too strongly squeezed been installed with too high a tightening torque.

Summarising, three important points can be given as follows:

For correct spark plug installation it is necessary to adhere strictly to the tightening torque and the installation instructions.

Tightening torque can also be determined at a later time.

Modern engines react particularly sensitively to incorrect installation.

Tightening torques for spark plugs with flat seat (with seal):
	18 mm	14 mm	12 mm	10 mm
Cast iron head	35-45 Nm	25-35 Nm	15-25 Nm	10-15 Nm
Aluminium head	35-40 Nm	25-30 Nm	15-20 Nm	10-12 Nm