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Spark Plug Torque Settings

It is extremely important that the correct torque is used when installing spark plugs. If a torque wrench is unavailable then you must take care not to overtighten spark plugs - particularly if refitting after cleaning. Most spark plugs (flat seat and gasket type) have a 'crush washer' or gasket which becomes compressed during the initial installation, this allows around half a turn of the plug to be made once contact with the cylinder head has been made by the gasket. Subsequent reuse of the plug will allow only one twelfth of a turn to be made after contact. Failure to observe this will often result in a damaged plug or cylinder head - to the extent of fracture or thread stripping. At best, an overtightened plug will not perform correctly - the plug's internal components will be 'stretched' and may not be able to dissipate heat correctly thus effectively increasing the heat range of the plug (making it run hotter and possibly overheat, plug and engine damage can result).

If using a tapered (conical and with no gasket) seat plug type, after contact of the 'shoulder' or mating surface of the plug is made, only one sixteenth of a turn should be applied. This applies to both new and re-used taper seat type plugs (common in Ford engines). In certain circumstances tapered seat plugs can be prone to 'seizing', this applies especially to certain models of Ford Fiesta and Ka. The best way to guard against problems of this type is to remove plugs midway between recommended service intervals and ensure that any corrosion is cleaned up before replacing (ideally. replace with new plugs).

Flat Seat Type (With Gasket) Conical Seat Type
Thread diameter 18mm 14mm 12mm 10mm 8mm 18mm 14mm
Cast iron head 34-45Nm 25-35Nm 15-25Nm 10-15Nm   20-30Nm 15-25Nm
  3.5-4.5kgm 2.5-3.5kgm 1.5-2.5kgm 1.0-1.5kgm   2.0-3.0kgm 1.5-2.5kgm
  25.3-32.5lbs ft 18.0-25.3lbs ft 10.8-18.0lbs ft 7.2-10.8lbs ft   14.5-21.6lbs ft 10.8-18.0lbs ft
Aluminium head 35-40Nm 25-30Nm 15-20Nm 10-12Nm 8-12Nm 20-30Nm 10-20Nm
  3.5-4.0kgm 2.5-3.0kgm 1.5-2.0kgm 1.0-1.2kgm 0.8-1.0kgm 2.0-3.0kgm 1.0-2.0kgm
  25.3-28.9lbs ft 18.0-21.6lbs ft 10.8-14.5lbs ft 7.2-8.7lbs ft 5.8-7.2lbs ft 14.5-21.6lbs ft 7.2-14.5lbs ft