RC12YC Spark Plug for BS 491055 491055S 491055T 792015 692051 694385 759-3336 John Deere M78543 M87543 Kohler 12 132 02 (Pack of 2)

What It Is

The RC12YC spark plug is a copper-core, resistor-type plug designed for small engines in lawn mowers, tractors, and other outdoor power equipment. It replaces OEM part numbers like Briggs & Stratton 491055, John Deere M78543, and Kohler 12 132 02, and is sold here as a pack of two for common twin-cylinder or backup use.

Fitment & Compatibility

Before buying, verify your engine’s model and spark plug gap requirement. This plug fits many Briggs & Stratton, John Deere, and Kohler engines, but it’s not universal. Check your current plug’s part number against the cross-references listed (491055, 692051, 759-3336, etc.). Measure the thread reach (3/4 inch) and hex size (5/8 inch) to confirm it matches your engine’s cylinder head. Do not rely on brand or deck size alone—always check your owner’s manual or existing plug for exact specs. This is an aftermarket replacement, not OEM, but meets or exceeds OEM performance standards.

Key Things to Buy

• Quality: Copper core provides reliable spark and good conductivity, but it wears faster than iridium or platinum plugs—expect replacement every 100 hours or annually.
• Installation: Simple plug swap—just remove the spark plug wire, unscrew the old plug, gap the new one to 0.030 inches (unless your engine specifies otherwise), and hand-tighten plus a quarter turn.
• Common gotcha: Over-tightening can damage threads in aluminum heads. Use a torque wrench (20 ft-lbs max) or just snug it by hand.
• Pack of two: Useful for twin-cylinder engines or as a spare, but single-cylinder mowers only need one.

Should You Buy It

If you need a budget-friendly, reliable replacement for a small engine that calls for the RC12YC or its cross-references, this pack delivers solid performance for the price. It’s ideal for routine maintenance on walk-behind mowers, riding tractors, or generators, but if you want longer life between changes, consider a platinum or iridium plug instead.