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Auto Parts / 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 spark plugs

The correct torque a glow plug, a compression loss The application of a tightening
For the professional installation of can result. Based on the torque which is too great, in
a glow plug, the use of a torque vibrations, it is also possible in the particular, can lead to the
wrench is recommended. Even for case of ceramic glow plugs that contraction of the annular gap
professionals the estimation of the ceramic will break. between the metal case and glow
the tightening torque is nearly tube. In this case the glow plug
impossible. overheats and fails.

That is because a torque can be
Tightening torque for Tightening torque for
calculated from two sizes which glow plugs the connecting nuts
are multiplied by one another: the
Thread Tightening Thread Tightening
force which is applied to the diameter torque diameter torque
respective centre of rotation and
8 mm 8-15 Nm 4 mm (M4) 0,8.1,5 Nm
the length of the handle.
10 mm 15-20 Nm 5 mm (M5) 3,0-4,0 Nm
If the incorrect torque is applied to
12 mm 20-25 Nm
14 mm 20-25 Nm
18 mm 20-30 Nm
Glow plugs will only function faultlessly when they are screwed in with the correct torques.

GB 3

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