NGK BU8H Standard Spark Plug - Fits 1978-1999 Mariner & 1978-2002 Mercury Outboards

The NGK BU8H is a Standard spark plug built for Mercury and Mariner outboard engines, cataloged by NGK under stock number 6431. It uses proven NGK Standard-plug technology: a copper-core center electrode for strong heat dissipation and reliable conductivity, paired with a nickel center electrode tip and a nickel Standard-configuration ground electrode. The shell and threads are corrosion-resistant plated, making installation and future removal easier and helping prevent seizing in a marine environment.

As an OE-cornerstone plug, the BU8H is designed to deliver consistent ignition performance over the plug's service life, supporting steady starting and running on the outboard powerheads it is built for. It carries a 1 ohm resistance rating and a ceramic insulator body for reliable spark energy transfer and heat handling.

This plug is fit for specific outboard applications, so confirm your engine and maintenance manual before ordering, and use only the plug your engine manufacturer recommends. Using the wrong plug can reduce performance and fuel economy or damage your engine.

Specifications

• Brand: NGK
• Manufacturer Part Number: BU8H
• NGK Stock Number: 6431
• Resistance: 1 ohm
• Ground Configuration: Standard
• Ground Electrode Core Material: Nickel
• Center Electrode Core Material: Copper
• Center Electrode Tip Material: Nickel
• Insulator Material: Ceramic
• Thread Size: 14mm
• Weight: 0.15 pounds
• UPC: 087295164310
• Unit Count: 1 spark plug

Fitment

• Outboard - Mariner, 1978-1999
• Outboard - Mercury, 1978-2002

Frequently Asked Questions

What engines does the NGK BU8H spark plug fit? The NGK BU8H, cataloged as stock number 6431, fits Mercury outboards from 1978 to 2002 and Mariner outboards from 1978 to 1999.

Is the BU8H a resistor spark plug? No, the NGK BU8H carries a resistance rating of 1 ohm, which is a standard, non-resistor ignition plug.

What electrode materials does the NGK BU8H use? The BU8H has a copper-core center electrode with a nickel tip, and a Standard-configuration ground electrode made of nickel.

What is the ground electrode configuration on the BU8H? The NGK BU8H uses a Standard ground electrode design, not a surface-discharge type.

How much does the NGK BU8H spark plug weigh? The NGK BU8H weighs 0.15 pounds.

What is the thread size of the BU8H spark plug? 14mm is the thread size of the NGK BU8H spark plug.

What is NGK stock number 6431? Stock number 6431 is NGK's catalog reference for the BU8H, a Standard spark plug built for Mercury and Mariner outboards.

Is the BU8H a genuine NGK plug or an aftermarket copy? The BU8H is a genuine NGK Standard spark plug, not an aftermarket substitute.

What insulator material is used in the BU8H? A ceramic insulator body is used in the NGK BU8H spark plug.

How many spark plugs come with this listing? One NGK BU8H spark plug is included per unit.

What is the UPC for the NGK BU8H spark plug? 087295164310 is the UPC for the NGK BU8H spark plug.