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Proper Bosch Gapping Instructions

If it is necessary to widen the gap, do so with a tool that only pulls back on the ground electrode without touching the center electrode or the porcelain. To close the gap on a plug, gently tap the plug, electrode first on a hard surface.

Bosch doesn't recommend adjusting the plug gap more than .008" in either direction. Beyond that slight adjustment, the ground electrode and center electrode won't align properly, hindering spark plug performance and drastically reducing plug life. 

  • Due to the fragile nature of their electrodes, special care should be taken when adjusting the gap on fine wire plugs.
  • It is not recommended that you adjust the gap on multi-ground plugs.
  • IR Fusion, +4, and +2 series plugs should never be gapped for any application.  The gaps on these plugs are not adjustable.

How to gap a spark plug