NGK 3981 Spark Plug

NGK Iridium IX Spark Plug 3981 Overview

NGK Iridium IX Spark Plug 3981 is built for precise ignition performance in applications that call for a 14 mm, flat-seat spark plug with a .75 reach and 13/16 hex. The iridium center electrode, nickel ground electrode, and 5,000 ohm resistance support stable spark delivery for demanding street and performance use.

Part number 3981 is also identified as BR9EIX and is part of NGK’s Iridium IX Spark Plug line, a product family focused on fine-wire iridium construction and consistent ignition characteristics. This spark plug is a direct-service option for riders and technicians looking for an NGK BR9EIX replacement, including applications cross-referenced to Bosch 3981 and DENSO 5317.

Key Features

• Iridium center electrode tip for durable spark performance
• Copper core center electrode for efficient heat transfer
• Nickel ground electrode with taper-cut tip design
• 5,000 ohm resistance for ignition system compatibility
• Pre-gapped at .032 for common service applications
• 14.00 mm thread diameter, .75 reach, flat seat
• Removable nut terminal type
• Heat range 9 for higher-temperature operating conditions

Detailed Product Description

NGK 3981 is an Iridium IX spark plug engineered around a fine iridium firing tip and a copper-core center electrode to promote consistent ignition under load. The taper-cut ground electrode design helps concentrate the spark path, while the standard single-ground configuration supports reliable combustion in compatible engines. With a .032 pre-gap, this plug is ready for service in many BR9EIX applications without additional setup.

As an NGK spark plug, 3981 reflects the company’s long OE manufacturing background and broad coverage across automotive, motorcycle, marine, and small engine categories. For buyers searching for NGK BR9EIX, NGK 3981, or an iridium spark plug replacement for select motorcycle and powersports engines, this part provides the specified dimensions and terminal style needed for proper fitment.

Compatible With select motorcycle and powersports applications that specify BR9EIX, including Yamaha and Honda models referenced by the listed interchange numbers.

What This Spark Plug Helps Address

• Misfire caused by worn or fouled spark plugs
• Hard starting from weak ignition output
• Rough idle linked to inconsistent spark delivery
• Loss of throttle response from degraded plug performance
• Service replacement needs for BR9EIX-spec ignition systems

Installation Notes and Tips

Verify the engine calls for a 14 mm, flat-seat plug with a .75 reach, 13/16 hex, and heat range 9 before installation. Confirm the terminal style matches the ignition lead or coil connection, and check the gap against the engine manufacturer’s specification if a different setting is required. Use proper torque procedures for the cylinder head material and thread condition.

Fits select Yamaha and Honda applications when the engine specification calls for NGK BR9EIX / 3981. Review the vehicle or equipment service data to confirm the exact application before installation.

Quality Assurance

NGK is a major OE spark plug supplier with decades of automotive and powersports manufacturing experience. Part number 3981 is produced to support original-equipment-style durability and operational consistency in the applications it was engineered for.