Replacement RN4C Spark Plug for Champion Lawn Mower Models

What It Is

The RN4C spark plug is a standard resistor plug designed for four-stroke engines in walk-behind mowers, including select Champion models. It delivers the spark needed for ignition and helps reduce radio interference.

Fitment & Compatibility

Before buying, confirm your mower’s engine model (not just the chassis) – the RN4C fits many Briggs & Stratton, Tecumseh, and Honda engines, but only certain Champion models. Check the Champion owner’s manual or the engine’s spark plug gap spec (typically 0.030″). Measure the thread reach (3/4″ for this plug) and hex size (13/16″). If your mower uses a different OEM plug number (e.g., J19LM, RJ19LM), the RN4C may cross-reference – verify via a spark plug cross-reference chart. This plug is not for two-stroke engines or zero-turn riders with larger engines.

Key Things to Know

• Gap must be set – The plug ships with a factory gap, but always check and adjust to your engine’s spec (0.030″ is common). Use a feeler gauge.
• Resistor type – Reduces electrical noise, which can interfere with electronic components on newer mowers. Fine for most standard mowers.
• Installation – Simple: remove the old plug with a spark plug socket, hand-thread the new one, then torque to 20-25 ft-lb. Over-tightening can strip the aluminum cylinder head.
• Common gotcha – The RN4C is shorter than some plugs (e.g., longer-reach J19LM). If your engine requires a long-reach plug, this won’t fit and can cause pre-ignition damage.

Should You Buy It

Buy this if you own a Champion walk-behind mower with a four-stroke engine that calls for an RN4C or a compatible cross-reference plug, and you want a reliable, no-fuss replacement at a reasonable price. It’s a solid choice for routine maintenance, but skip it if your engine needs a different reach or gap spec.