Briggs & Stratton 591868 Spark Plug

What It Is

The Briggs & Stratton 591868 spark plug is a direct replacement plug for many Briggs & Stratton single-cylinder lawn mower engines, as well as some small engines from other brands. It’s a standard copper-core, resistor-type plug (equivalent to a Champion RJ19LM or Autolite 216) used for reliable ignition in push mowers, riding mowers, and other power equipment.

Fitment & Compatibility

Before buying, check your engine’s model number and specifications. This plug fits most Briggs & Stratton engines with a 14mm thread diameter, 19mm (3/4-inch) reach, and a 13/16-inch hex size. It’s commonly used on engines like the 400000, 420000, 440000, and 450000 series, but also works on many older models. If you have a non-Briggs engine (e.g., Tecumseh, Kohler, Honda), verify your owner’s manual or current plug gap. The gap for this plug is usually 0.030 inches, but always confirm your engine’s spec (some older engines use 0.025 or 0.035). Measure the thread length and hex size on your old plug to be sure. It’s OEM-spec, so no adapter needed.

Key Things to Know

• Quality: Copper-core plug; good for standard use, but not a long-life (iridium/platinum) plug. Expect 50–100 hours of use before replacement.
• Installation: Easy—just remove the spark plug boot, unscrew with a 13/16-inch socket, gap to 0.030 inches, hand-tighten then 1/2 turn with a wrench. Over-tightening can strip threads.
• Common gotchas: The plug is pre-gapped, but always check and adjust with a feeler gauge—shipping can knock it off. If your engine has a small gap (e.g., 0.020), this plug won’t work. Also, it’s not for high-compression or high-RPM engines (e.g., some V-twins or commercial models).
• Fitment note: Works with both standard and resistor-type ignition systems, but if your engine requires a non-resistor plug, avoid this one.

Should You Buy It

If you have a standard Briggs & Stratton single-cylinder mower engine and need a budget-friendly, reliable replacement for routine maintenance, this is a solid choice. It’s not for performance or extended-life applications, but for the price and fitment coverage, it’s the go-to for most homeowners. Skip it if your engine needs a different gap or a non-resistor plug.