How to Change Spark Plugs | Torque Spec Chart

How to Change Spark Plugs - Spark Plugs Methods of Sealing, Spark Plugs Installation and Spark Plug Gap Chart sections of this page are here to help you better understand the most critical steps and procedures in changing spark plugs.  

When replacing spark plugs, BASIC IDENTIFICATION OF SPARK PLUG - is necessary for determination of the correct spark plug installation troque.

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

Methods of spark plugs sealing in the engine cylinder head:

Conical seat - Spark plug is sealed in cylinder head with a conical (tapered) seat.

Spark Plug Gap | Spark Plug Gap Chart

In this case no sealing washer is used. The assembly of spark plug with this kind of sealing requires an especially sensitive approach.  For proper spark plug installation, it is always highly recommended to use spark plug removal and installation tool and spark plug torque wrench.  Correct torque is the very most critical step of spark plug installation.  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...  It is extremly important not to exceed the installation torque. However in order to ensure proper seating of a conical seat spark plug, it is a good idea to torque the spark plug, loosen it a 1/4 turn and torque it again. This will help ensure proper seating and adequate heat transfer.  This goes for conical seat spark plugs only!

 

 

 

 

How to change conical (tapered) seat spark plug without torque wrench - (only if torque wrench can not be obtained)

TIGHTENING by ANGLE 

When replacing spark plugs without spark plug torque wrench, spark plugs should be thread-in by spark plug removal and installation tool, or socket by hand (wihtout spark plug wrench) untill they fully seat.  Then a spark plug wrench should be used to tighten the spark plug by turning an additional angle as follow:

new spark plug         used spark plug 

 

Sealing with a gasket (washer) - spark plugs can never be mounted into cylinder head without a sealing gasket (washer).

Spark Plug Gap

In this case sealing washer must be used (comes with new spark plugs).  If gasket style spark plug is installed without sealing gasket, the combustion area will not seal sufficiently and heat removal (transfer of heat from the spark plug into the engine cylinder head) will not be sufficient.  When replacing spark plugs, for proper spark plug installation it is always highly recommended to use spark plug removal and installation tool and spark plug torque wrench. Correct spark plug torque is the very most critical step of spark plug installation. It is extremely important to never exceed the spark plug recommended installation torque.





 

 

 

How to change gasket (washer) style spark plug without torque wrench - (only if torque wrench can not be obtained)

TIGHTENING by ANGLE


When replacing spark plugs without spark plug torque wrench, spark plugs should be threaded-in by spark plug removal and installation tool, or socket by hand (without spark plug wrench) untill they fully seat.  Then a spark plug wrench should be used to tighten the spark plug by turning an additional angle as follow:

new spark plug           used spark plug

 

 

How to Change Spark Plugs - Replacing Spark Plugs using torque wrench

IMPORTANT !!! - When replacing spark plugs, the engine must be close to the ambient temperature.  The area around the spark plugs should be cleaned with compressed air (or air in the can) to prevent foreign debree from falling into the combustion chamber.  Spark plug and cylinder head threads needs to be free of carbon build up, clean, and it is recommended, free of lubricant.  If needed, cylinder head threads can be cleaned by spark plug thread chaser in the correct size thread (10mm, 12mm, 14mm).  If spark plug thread lubricant (antisieze) is used when replacing spark plugs, it shoud be used very sparingly on the spark plug thread only and the spark plug installation torque is to be reduced by about 25% ! 

However, it is highly recommended to use spark plug dielectric grease in the spark plug wire cable boot, or Coil on Plug boot prior connecting to the spark plug.  This ensures air tight connection which prevents spark flash-over (spark on the outside of the spark plug between the spark plug High Voltage terminal and the spark plug shell) which will cause spark plug missfire and engine hesitation.  Dielectric grease prevents missfires, keeps the moisture out, and ease the future removal of the spark plug wire or the spark plug boot.

How to Change Spark Plugs - Spark Plug Torque Chart specs in (N.m.)

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

 

How to Change Spark Plugs - Spark Plug Torque Chart specs in (ft.lb)

SPARK PLUG

HEAD OF ENGINE

plug sizes

seals

cast - iron

aluminum

M 10 x 1

sealing ring

7.2-10.8 ft.lb

7.2-8.7 ft.lb

M 12 x 1,25

sealing ring

10.8-18 ft.lb

10.8-14.5 ft.lb

M 14 x 1,25

sealing ring

18-25.3 ft.lb

18-21.6 ft.lb

M 14 x 1,25

conical seat

10.8-18 ft.lb

7.2-14.5 ft.lb

M 18 x 1,5

conical seat

14.5-21.6 ft.lb

14.5-21.6 ft.lb

How to Change Spark Plugs - Spark Plug Torque Chart sepecs in (in.lb)

SPARK PLUG

HEAD OF ENGINE

plug sizes

seals

cast - iron

aluminum

M 10 x 1

sealing ring

86-130 in.lb

86-104 in.lb

M 12 x 1,25

sealing ring

130-216 in.lb

130-174 in.lb

M 14 x 1,25

sealing ring

216-304 in.lb

216-259 in.lb

M 14 x 1,25

conical seat

130-216 in.lb

87-174 in.lb

M 18 x 1,5

conical seat

174-259 in.lg

174-259 in.lb