Spark Plug Installation and Spark Plug Gap setting


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

Methods of spark plugs sealing

Conical seat Spark plug is sealed in cylinder head with a conical (tapered) 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...  It is important not to exceed the installation torque, however it is a good idea to torque the spark plug, loosen it a 1/4 turn and torque it again to ensure proper seating and adequate heat transfer.  This goes for conical seat spark plugs only.



 

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.  As always it is important to never exceed the required installation torque.





Tightening of spark plugs without using a torque wrench

  
 

Spark plug Torque table 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

Spark plug Torque table 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

Spark plug Torque table 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

Spark plug Gap setting and Gap cross-refference chart

The very most important rule when checking or adjusting spark plug gap is, to never pry, apply or exert any force on the center electrode, or center electrode ceramic insulator.  The force should be applied only on the ground electrode strap moving it closer or further away from the spark plug center electrode. The spark plug gap adjustment should not be changed more than 3 times and should not exceed .008" in either direction.  Also, the spark plug gap should never exceed .055" unless pre-set by the manufacturer.

Most Brisk and other manufacturer sparkplugs are preset to around 0.75mm - 0.8mm. If your spark plug part number has no trailing digits then (for most part numbers) it will be preset to this specification.  The exception are for example spark plug part numbers with gap can not be changed such as Brisk Premium Multi-spark plugs, Brisk Premium LGS Spark Plugs, Brisk Premium LGS-T spark plugs (the -T indicate LGS style spark plug with a Tighter gap than standard LGS style spark plug and should be used on applications where the recommended gap setting is less than .032"), Brisk Extra Turbo Spark Plugs and some others.  If there are trailing numbers after the part number, then the gap should be specifically set as per the manufacturer's part code designation (e.g. Brisk RR15IRY-7, gap size is 0.7 mm, Brisk GOR15YTE-3, gap size is 1.3mm NGK BKR6E-11, gap size is 1.1mm, Denso T16EPR-U15, gap size is 1.5mm, Champion RC10YC4, gap size is 1.0mm). Part numbering for Brisk, NGK and Denso is reasonably logical with the trailing digits transposing directly into size in mm. For Champion it is a little less logical and is as listed below: 

4 = 1.0mm (e.g. RC10YC4) 
5 = 1.3mm (e.g. RN16YC5) 
6 = 1.5mm (e.g. RS14YC6)

Spark Plug Gap cross-refference chart - metric to standard (mm to inch)

mm0.40.50.60.70.80.91.01.41.51.61.71.81.92.0
inch.016".020".024".028".032".035".039".055".059".063".067".071".075".079"

Spark Plug 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 Spark Plug threaded shell