NGK Spark Plug – BPR4ES

The NGK BPR4ES is a standard copper-core nickel spark plug used in select small engines, utility equipment, ATVs, powersports applications, and outdoor power equipment where the manufacturer specifies the BPR4ES / NGK 6578 plug profile. It features a projected insulator nose, built-in resistor, 14 mm gasket-seat body, and NGK’s standard nickel firing-end construction for dependable everyday ignition service in compatible engines.

This plug should be installed only where the engine service manual, equipment label, or factory application chart specifically calls for NGK BPR4ES, NGK 6578, or an approved equivalent.

Key Features

• Genuine NGK standard spark plug.
• NGK part number: BPR4ES.
• NGK stock number: 6578.
• Copper-core nickel construction for standard service applications.
• Built-in resistor to help reduce ignition-related RFI noise.
• Projected insulator nose design.
• Thread diameter: 14 mm / M14 x 1.25.
• Thread reach: 19 mm / 3/4 in.
• Hex size: 13/16 in. / 21 mm.
• Seat style: flat / gasket seat.
• Heat range: 4.
• Factory preset gap reference: 0.032 in. / 0.8 mm.
• Commonly used in select small-engine, lawn care, ATV, generator, pressure washer, and utility-equipment applications where specified.

Application Compatibility

Common application context includes select engines and equipment where the factory plug chart calls for NGK BPR4ES / 6578, including:

• Select small air-cooled utility engines where specified
• Select Kawasaki-powered lawn and turf equipment where specified
• Select pressure washer, generator, chipper, and outdoor power equipment applications where specified
• Select ATV, utility cart, and powersports applications where the manufacturer lists BPR4ES
• Other equipment requiring a 14 mm, 19 mm reach, gasket-seat resistor plug with projected-tip construction

Use this spark plug only where the manufacturer’s application chart specifically lists BPR4ES, 6578, or an approved equivalent.

Fitment Notice

Confirm fitment by exact equipment brand, engine model, serial number, service manual, and factory spark plug chart before ordering. Spark plugs with the same thread diameter can still differ in reach, heat range, seat style, projection, terminal style, resistor specification, and required gap. Installing the wrong plug can cause hard starting, misfire, poor idle, overheating, thread damage, piston contact, or ignition-system issues.

When This Part Needs Replacement

Replace spark plugs during scheduled tune-up service or whenever the plug is worn, fouled, fuel-soaked, oil-contaminated, cracked, corroded, damaged, or causing hard starting, rough idle, hesitation, weak acceleration, misfire, or poor low-speed running. Small engines that idle frequently, run under dusty load, or sit in seasonal storage should have spark plugs inspected regularly.

Installation Notes

Check the plug number and required gap against the engine service chart before installation. Install into clean, undamaged cylinder head threads and tighten to the manufacturer’s torque specification for the exact engine. Because this is a gasket-seat plug, confirm the sealing washer is present and seats correctly.

Avoid adding anti-seize unless the engine or spark plug manufacturer specifically calls for it, as thread lubricant can change clamping load and increase the risk of over-tightening. Confirm the terminal style matches the ignition boot before installation.

Alternate/Superseded Part Numbers

• NGK BPR4ES spark plug part number
• NGK 6578 NGK stock number
• BPR4ES Standard product style reference
• Honda 98079-54817 cross-reference; verify by engine model and plug chart
• Honda 98079-54846 cross-reference; verify by engine model and plug chart
• Kawasaki 92070-7004 cross-reference; verify by engine model and plug chart
• Kawasaki 92070-2112 cross-reference; verify by engine model and plug chart
• Denso W14EPR-U / W14EPRU cross-reference; verify by application
• Champion RN11YC / RN12YC / RN14YC cross-reference; verify by application

Parts Desk Insight

The BPR4ES is a hotter heat-range plug often used in small engines that spend time at light load, idle, or intermittent duty. Match it by exact plug number, reach, seat style, heat range, and required gap rather than by equipment type alone. A hotter plug can help resist carbon fouling in the right application, but the wrong heat range can create poor running or engine damage.

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