Gap a sparkplug by cleaning the plug, selecting the correct wire gauge, testing the gap and adjusting the electrode. Check and adjust pregapped plugs from the factory due to potential changes that may occur in shipping.
- Select the right spark plug for the engine
If replacing spark plugs on a vehicle, check the manufacturer's guide to ensure you are purchasing the correct plugs for the vehicle and that the thread reach is correct for the engine cylinder.
- Clean and inspect the plug
If checking the gap on a used spark plug, clean it with a small wire brush before attempting to gap it. Replace any plug that has cracked porcelain, missing threads or badly burned electrodes.
- Select the correct wire gauge
Determine the correct wire gauge by consulting the owner's manual or service manual for your vehicle. Engines that operate with high compression require a smaller gap.
- Test the gap
The wire gauge should pass through the electrode opening with slight resistance.
- Adjust the gap
If the wire does not pass through the gap, increase the gap using the adjustment tool on the gauge to bend the electrode slightly. If the wire passes through with no resistance, press the electrode firmly on a hard surface to close the gap slightly. Retest and adjust the electrode as necessary.