NGK PKW Katalog 2012-2013

Tightening torques for spark plugs
Torques
A torque wrench is required for
the professional installation of a
spark plug. Even for professionals
the estimation of the tightening
torque is nearly impossible.
That is because a torque can be
calculated from two sizes which
are multiplied by one another: the
force which is applied to the
respective centre of rotation and
the length of the handle.
Cylinder head
material
Cast iron head
Aluminium head
Thread
diameter
18 mm
35-45 Nm
35-40 Nm
Spark plug with flat seat Spark plug with
(with gasket) conical seat
Thread diameter Thread diameter
14 mm
25-35 Nm
25-30 Nm
Tightening torque for Tightening torque for
glow plugs the connecting nuts
Tightening
torque
12 mm
15-25 Nm
15-20 Nm
Tightening torques for spark plugs
The correct torque
For the professional installation of
a glow plug, the use of a torque
wrench is recommended. Even for
professionals the estimation of
the tightening torque is nearly
impossible.
That is because a torque can be
calculated from two sizes which
are multiplied by one another: the
force which is applied to the
respective centre of rotation and
the length of the handle.
If the incorrect torque is applied to
Most spark plug failures can be
traced back to an incorrect
tightening torque. If it is set too
low, there is a risk of compression
losses and overheating. A break
of the insulator or middle
electrode as a result of vibrations
is also feasible.
10 mm
10-15 Nm
10-12 Nm
Thread
diameter
18 mm
20-30 Nm
20-30 Nm
The torques depend on the cylinder head material and the thread diameter.
a glow plug, a compression loss
can result. Based on the
vibrations, it is also possible in the
case of ceramic glow plugs that
the ceramic will break.
Tightening
torque
14 mm
15-25 Nm
10-20 Nm
8 mm
8-15 Nm
4mm(M4) 0,8.1,5 Nm
10 mm
15-20 Nm
5 mm (M5) 3,0-4,0 Nm
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.
IS
3
If the tightening torque is set too
high, the spark plug can snap off.
The casing can also expand or
warp. Heat dissipation zones are
disrupted, overheating and
melting of the electrodes or even
engine damage can occur.
The application of a tightening
torque which is too great, in
particular, can lead to the
contraction of the annular gap
between the metal case and glow
tube. In this case the glow plug
overheats and fails.