Spark Plug Install Torque Recommendations

Spark Plug Installation Torque Settings & Recommendations

It is extremely important that the correct torque is applied when installing spark plugs. If an accurately scaled, recently calibrated torque wrench is unavailable then you must take care not to overtighten spark plugs - particularly if refitting after cleaning or checking and setting the spark gap. We strongly recommend using the manual tightening method described below rather than relying on an unsuitable or uncalibrated torque wrench. Most cases of over torquing damage to spark plugs we have come across have been due to use of an unsuitable or inaccurate torque wrench.

Most spark plugs (flat seat with gasket type) have a 'crush washer' or gasket which becomes compressed during the initial installation, this allows around half a tightening turn of the plug to be made once contact between cylinder head and gasket has been established. Once the gasket has contacted the cylinder head we would term it is 'finger tight'. Subsequent reuse of the plug will allow only one twelfth of a turn to be made after contact due to the gasket already having been compressed and as a result installation torque being reached much more quickly. Failure to observe this guideline may 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 spark 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 may result..

If using a tapered (conical, without gasket) seat plug type, after contact of the 'shoulder' or mating surfaces of the spark plug and cylinder head 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 spark 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.

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