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NGK_Katalog_ZK_GK_2016_2017_Reihenfolge_rz_Layout 1 11.05.16 10:48 Seite 28

Tightening torques for spark plugs

Torques Most spark plug failures can be If the tightening torque is set too
A torque wrench is required for traced back to an incorrect high, the spark plug can snap off.
the professional installation of a tightening torque. If it is set too The casing can also expand or
spark plug. Even for professionals low, there is a risk of compression warp. Heat dissipation zones are
the estimation of the tightening losses and overheating. A break disrupted, overheating and
torque is nearly impossible. of the insulator or middle melting of the electrodes or even
electrode as a result of vibrations engine damage can occur.
That is because a torque can be is also feasible.
calculated from two sizes which
are multiplied by one another: the
force which is applied to the Spark plug with flat seat Spark plug with
(with gasket) conical seat
respective centre of rotation and
the length of the handle. Cylinder head Thread diameter Thread diameter
material 18 mm 14 mm 12 mm 10 mm 18 mm 14 mm
Cast iron head 35-45 Nm 25-35 Nm 15-25 Nm 10-15 Nm 20-30 Nm 15-25 Nm

Aluminium head 35-40 Nm 25-30 Nm 15-20 Nm 10-12 Nm 20-30 Nm 10-20 Nm
The torques depend on the cylinder head material and the thread diameter.

Tightening torques for glow plugs

The correct torque force which is applied to the The application of a tightening
For the professional installation of respective centre of rotation and torque which is too great, in
a glow plug, the use of a torque the length of the handle. particular, can lead to the
wrench is recommended. Even for contraction of the annular gap
professionals the estimation of If the incorrect torque is applied to between the metal case and glow
the tightening torque is nearly a glow plug, a compression loss tube. In this case the glow plug
impossible. can result. Based on the overheats and fails.
vibrations, it is also possible in the
That is because a torque can be case of ceramic glow plugs that
calculated from two sizes which the ceramic will break.
are multiplied by one another: the

Please follow the instruction if specified tightening torque or angle is mentioned on the package !!!

Tightening torque for
Metal Glow Plug Ceramic Glow Plug
the connecting nuts
Thread diameter Thread diameter Thread Tightening
diameter torque
M8 M9 M10 M12 M14 M8 M10
8,5 Nm 11 Nm 15 Nm 23 Nm 23 Nm 10 Nm 18 Nm 4 mm (M4) 0,8–1,5 Nm
+/- 10 +/- 10 +/- 10 +/- 10 +/- 10 +/- 10 +/- 10 5 mm (M5) 3,0–4,0 Nm

Glow plugs will only function faultlessly when they are
screwed in with the correct torques.

GB 28