SPARK PLUG Installation

It is necessary to install the plugs in the engine using the correct torque. Note that if the torque is too low, the plugs are liable to work loose due to leakage of combustion gas or vibration, resulting in possible damage to the engine and the plugs. Conversely, if the torque is too high, the crimping between the insulator and the housing is liable to become loose, causing the integrity of the seal to be impaired or the mounting screw thread to break.

  1. Use the correct wrench that matches the hex part of the plug. Take care not to damage the insulator.
  2. When carrying out this work, take steps to ensure that oil, dust and foreign objects in the vicinity of the cylinder head do not enter the engine.
  3. Before installing the plug, clean the mounting seat on the engine side, check that there is a gasket, and then insert the plug into the mounting seat.
    Before installing the plug, clean the mounting seat on the engine side, check that there is a gasket, and then insert the plug into the mounting seat.
  4. When carrying out this work, hold the plug vertically, and then lightly tighten it by hand or by using a plug wrench.
    When carrying out this work, hold the plug vertically, and then lightly tighten it by hand or by using a plug wrench.
  5. Next, using a plug wrench, tighten the plug to the recommended torque or the recommended angle indicated in the table below.

If you tighten the plug to a greater rotation angle or torque than that indicated in the table below, the engine may become damaged or the screw thread of the plug may break, so be careful.

If you apply grease or another screw thread lubricant to the threaded part of the plug, you are liable to tighten the plug to an excessive degree, impairing the integrity of the seal, even if you apply no more than the recommended torque. For this reason, do not coat the plug with screw thread lubricant.

If you apply the plug wrench obliquely, an unreasonable force may be applied to the insulator, causing it to crack, as indicated in the figure below. For this reason, be careful not to hold the wrench obliquely.

Thread Size Recommended
Torque
Applicable Models Recommended Tightening Angle
New Plug Previously Used
M 8 8-10N・m All Types About 1/3 turn About 1/12 turn
M10 10-15N・m Types other than the ones shown below About 1/3 turn About 1/12 turn
M10 10-15N・m UFE, IUH, VUH, VNH Types About 2/3 turn About 1/12 turn
M10 10-15N・m Stainless Gasket Type (*1) About 3/4 turn About 1/12 turn
M12 15-20N・m All Types About 1/3 turn About 1/12 turn
M14 20-30N・m Types other than the ones shown below About 1/2 turn About 1/12 turn
M14 20-30N・m Stainless Gasket Type (*2) About 2/3 turn About 1/12 turn
M18 30-40N・m All Types About 1/4 turn About 1/12 turn
M14
Taper seat
10-20N・m All Types About 1/16 turn About 1/16 turn
M14
(Gas)
20N・m If the cylinder head material is cast iron - -
M14
(Gas)
17.5N・m If the cylinder head material is aluminum - -
M18
(Gas)
30N・m If the cylinder head material is cast iron - -
  • (*1) VUH27ES,U24FER9S
  • (*2) IK16G,IK20G,IK22G,K20PR-U8S,K20PR-U9S,KJ20DR-M11S,PK22PR-L11S,SK20PR-N9S,SK22PR-M11S,SKJ20DR-M11S,VK16G,VK20G,VK22G

Cracking of the insulator

The plugs of recent engines are installed in deep plug holes, so it may be difficult to notice whether or not you are holding the wrench obliquely when installing or removing the plugs. However, if you turn the wrench in this condition, the head of the insulator may stick , causing an unreasonable force to be applied to it. As a result, the insulator is liable to crack.

Cracking of the insulator

*However, the mode of occurrence differs according to the construction and dimensions of the plug holes in the engine, and also the type of wrench used.