491055S Spark Plug Replacement | Compatible with Champion RC12YC, NGK BKR6ES, Kohler & Briggs & Stratton Lawn Mower Engines, 2 Pack

What It Is

This is a set of two aftermarket spark plugs (model 491055S) designed to replace Champion RC12YC or NGK BKR6ES plugs in Kohler, Briggs & Stratton, and other small engines found on walk-behind lawn mowers, riding mowers, and some generators or pressure washers.

Fitment & Compatibility

Before buying, confirm your engine’s spark plug specifications. The 491055S has a 14mm thread diameter, 19mm (3/4”) reach, and a gasket seat. It requires a 13/16” (21mm) socket for installation.

• Cross-references: Replaces Champion RC12YC, RC12Y, J19LM; NGK BKR6ES, BPR6ES; Autolite 3924; and many Kohler and Briggs & Stratton OEM numbers.
• Check your engine model: Works on most Kohler Courage, Command, and Pro series, and Briggs & Stratton Intek, Quantum, and Vanguard engines. Not suitable for small 2-stroke trimmers or chainsaws.
• Gap: Must be set to 0.030” (0.76mm) before installation. The plug comes pre-gapped but verify with a feeler gauge—shipping can shift it.

Key Things to Know

• Quality: Mid-range aftermarket plug. Fine for seasonal use but may not last as long as OEM Champion or NGK in high-vibration or heavy-duty commercial mowers.
• Installation: Easy. Remove the old plug, check gap, hand-thread until snug, then tighten 1/2 turn with a socket. Overtightening can strip the aluminum cylinder head.
• Common gotcha: The gasket seat must be clean and flat. Dirt or old gasket residue can cause a poor seal and misfire.
• 2-pack value: Convenient if you have two compatible engines or want a spare. Single plugs are often cheaper per unit, but this pack saves a trip.

Should You Buy It

If you need a quick, budget-friendly replacement for a standard residential mower with a Kohler or Briggs engine, this 2-pack works fine. Skip it if you run a commercial machine, want maximum plug life, or need a specific electrode design for high-performance engines—stick with OEM Champion or NGK.