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Correct Mounting

Spark plugs are constructed by using two different manners of sealing in cylinder head.

Methods of spark plugs sealing

  • Conical Seat
    Conical Seat
    Spark plug is sealed in cylinder head with a conical seat. In this case no sealing washer is used. The assembly of spark plugs with this kind of sealing requires an especially sensitive approach. If the torque is exceeded, the spark plug shell can be stretched, thermal characteristics can be lost and there may even occur a rupture of the spark plug during its assembly or dismantling in the engine.
  • Sealing with a washer
    Sealing with a Washer
    Spark plugs can never be mounted into cylinder head without a sealing washer. In such a case the combustion area is not sealed sufficiently and heat removal into cylinder head does not work well enough.

Tightening of spark plugs without using a torque wrench

Conical (tapered) Seat

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New Spark Plug
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Old Spark Plug

Gasket (washer) Style

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New Spark Plug
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Old Spark Plug

Torque table

Spark Plug Head of Engine
plug sizes seals cast - iron aluminum
M 10 x 1 sealing ring 10 - 15 Nm 10 - 15 Nm
M 12 x 1,25 sealing ring 15 - 20 Nm 15 - 25 Nm
M 14 x 1,25 sealing ring 20 - 40 Nm 20 - 30 Nm
M 14 x 1,25 conical seat 10 - 20 Nm 10 - 20 Nm
M 18 x 1,5 conical seat 20 - 30 Nm 20 - 30 Nm

Selection of proper spark plugs

Heat range
Vehicles produced in series (which are not additionally modified for engine power output enhancement), whose engines are properly adjusted and in good technical condition, can be equipped according to the current application tables.

Any comparison charts of spark plugs are always for informative purposes only and they do not substitute the current application tables in full.

In the case of engine power output enhancement by means of additional modifications it is suitable to contact a producer's representative. There always applies a principle that in the case of medium modifications of the power output it is suitable to use the spark plugs "colder" by 2 degrees than those forming its original equipment (e.g. a change from 15 to 12). After driving several miles and subsequent assessment of the insulator tip appearance it is possible to decide about the most suitable equipment. This operation requires enough experience.

Proper length of the threaded shell

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