Spark Plugs for M5Di & M6Di 

LT4 Uses SKU: E100219

Tools required: Ratchet, 5/8” deep socket, extension, marine-grade dielectric grease, spark plug gap checker.

How to Remove, Inspect and Change Spark Plugs:

1. Before starting, be sure that the engine has cooled. Heat can cause the threads to strip when removing spark plugs.

2. Turn the boot approximately 90 degrees counterclockwise and then pull off the spark plug. There should be an audible “pop” when it releases. If not, check with the customer to determine if the engine had been misfiring.

3. Before removing the spark plug, use a clean cloth or an air hose to clean the engine area around the void. You will want to avoid getting dust, dirt, oil, grease, or any traces of dielectric grease inside the spark plug housing.

4. Using the 5/8” deep socket and extension with the ratchet attached, break loose the torque on the spark plug.

5. After the torque tightenting has been loosened, remove the ratchet from the from the extension. You will find it easier to finish removing the spark plug by hand.

5. After the torque tightenting has been loosened, remove the ratchet from the from the extension. You will find it easier to finish removing the spark plug by hand.

7. Pictured is a new spark plug. A used one should be evenly grayish-tan on the firing tip. There should not be carbon deposits on the tip. The used spark plug should also be dry. If any of these situations appear, contact your Engine Technical Representative as they are signs of bigger issues.

8. You will want to check the gap on both the OLD spark plug and the NEW one. Our engines use the AC Delco 41-114 spark plug, pre-gapped at 0.40”.

9. AC Delco does allow a maximum of 0.002” tolerance.

10. To reinstall the spark plug or install a new one, slide the spark plug into the socket attached to the extension, with the firing tip exposed.

11. Hand tighten until snug.

12. Then attach the ratchet and torque to only 16-24 ft. lbs. Too little and the engine will misfire. Too much and the spark plug will break inside the engine. Remove the pieces is especially difficult.

13. After the spark plug has been installed, add a SMALL amount of dielectric grease inside the boot. This will ease installation of the boot, and will ensure an easier removal in the future maintenance. It will also repel water and other fluids.

14. Whenever there is an engine misfire or other runability issues, be sure to check the spark plugs. Regardless, spark plugs should be cleaned every 300 hours, and changed every two years, whichever comes first.