2024 International MV Spark Plug Specs: Type, Gap & Torque

As an ASE-certified master technician, I regularly get questions about medium-duty trucks and their maintenance schedules. When it comes to the 2024 International MV series, there is a major distinction you need to understand right away: the standard engines for this truck are the Cummins B6.7 and L9 diesels, which utilize compression ignition and do not have spark plugs.

However, International offers the MV series with the Cummins L9N, a dedicated Natural Gas (CNG/LNG) engine. Unlike its diesel counterparts, the L9N is a spark-ignited engine that relies heavily on high-quality spark plugs to ignite the compressed natural gas. Below is the essential spark plug data for fleet managers and technicians working on the spark-ignited L9N.

Quick reference

(Note: Cummins frequently updates exact part numbers for their natural gas engine spark plugs to combat high-temperature degradation. Always verify the current superseded OEM Cummins part number via your dealer using your specific Engine Serial Number (ESN).)

Why the right plug matters

Choosing the correct spark plug for a natural gas engine like the Cummins L9N is vastly different from a standard gasoline engine. Natural gas burns much hotter and significantly drier than gasoline, lacking the cooling and lubricating properties of liquid fuel.

Because of this extreme combustion environment, standard copper or even standard platinum plugs will fail rapidly. The OEM-specified plugs utilize ultra-durable iridium electrodes designed with a highly specific heat range to dissipate the intense thermal loads of CNG combustion. Installing a plug with the wrong heat range or inferior electrode metal will lead to pre-ignition, severe detonation, or catastrophic piston damage.

How to gap a spark plug

Even if your premium iridium plugs say "pre-gapped" on the box, I always verify the gap before installation—especially with the ultra-tight 0.015-inch gap required for the L9N.

1. Use the right tool: Never use a cheap coin-style gauge on iridium plugs; dragging it across the center electrode can easily snap the brittle iridium tip. Use a precision wire feeler gauge.
2. Measure gently: The wire should pass between the center and ground electrode with a slight "drag."
3. Adjusting the gap: If adjustment is needed, use the bending tool on the gauge to apply a light bend to the ground strap only. Never pry against the center iridium electrode.

Replacement procedure tips

Working on the Cummins L9N requires distinct procedures compared to traditional automotive spark plug changes.

• Coil-on-Plug (COP) System: The L9N utilizes an advanced coil-on-plug ignition system with specialized coil boots to seal out moisture. Carefully twist the coil boots back and forth before pulling up to prevent tearing the silicone.
• The Anti-Seize Debate: Most modern NGK-manufactured plugs feature a specialized trivalent metal plating that prevents seizing in the aluminum cylinder head. Adding anti-seize acts as a lubricant, which can easily cause you to over-torque the plug and strip the threads. Install them dry unless the specific Cummins service manual for your ESN explicitly calls for a specialized high-temp thread paste.
• Dielectric Grease: Always apply a small dab of dielectric grease to the inside of the coil boot. This prevents the boot from fusing to the plug's ribbed porcelain over the 1,500-hour service interval and helps prevent high-voltage flashover.

Known issues

The biggest issue with spark-ignited heavy-duty natural gas engines is spark flashover and boot degradation. Because CNG requires a very high firing voltage to ignite, electricity will always look for the path of least resistance. If the coil boots become brittle from the extreme engine heat, the spark will blow right through the side of the boot and ground out on the cylinder head, causing a severe misfire under load. Whenever you replace the plugs on an L9N, it is highly recommended to inspect the coil extensions and replace them if they show any signs of chalking, cracking, or carbon tracking.

Need plugs replaced? Find a shop on Repairius.