How to Gap a Spark Plug

New DENSO spark plugs are pre-gapped and do not need changing. It is also important to note that DENSO plugs with a U-groove ground electrode require a special gap feeler gauge due to the U-groove.

The information below is provided as a general guide only. Please refer to your owner’s manual or the spark plug manufacturer for further information.

  • To check the gap of a spark plug use a feeler gauge and choose the correct wire to match the stated plug gap.
  • Run the wire between the electrodes, it should pass through fairly easily, just catching as it passes.
  • Adjust the gap if required
  • To widen gap - use the correct part of the gauge to hook on the ground electrode and gently tug.
  • To narrow gap - press the ground electrode against a soft, clean surface very gently.
  • Re-check gap until it is correct.

This guide is provided for informational purposes only. Always seek the advice of a trained professional before servicing any engine. DENSO is not responsible for the use or misuse of this information and any results thereof. Specifications subject to change without notice.