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Marine & Outboard Spark Plugs

NGK Nickel Spark Plug BR9HS-10 (4551)

SKU: GB-BR9HS-10

$8.80
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The NGK BR9HS-10 (Stock No. 4551) is a resistor-type spark plug designed for selected 2-stroke marine outboards requiring a colder NGK heat range 9 plug. It features an M14 × 1.25 thread, 12.7 mm reach and 1.0 mm gap, with resistor suppression to help reduce ignition interference. BR9HS-10 is specified for selected Mercury, Mariner, Yamaha and other outboard applications.

Key benefits

Key Benefits

  • - Resistor-type spark plug
  • - Helps suppress electrical/RFI interference
  • - NGK heat range 9
  • - Short 12.7 mm / 1/2" reach
  • - 1.0 mm / 0.040" spark gap
  • - M14 × 1.25 thread
  • - Standard non-projected electrode configuration
  • - Flat / gasket seat
  • - Suitable for selected 2-stroke outboard motors
  • - Direct replacement where BR9HS-10 is specified

Specifications & Dimensions

  • - Brand: NGK
  • - Part Number: BR9HS-10
  • - NGK Stock Number: 4551
  • - Spark Plug Type: Standard resistor
  • - Thread Diameter: 14.0 mm / 0.551"
  • - Thread Size: M14 × 1.25
  • - Thread Pitch: 1.25 mm / 0.049"
  • - Thread Reach: 12.7 mm / 0.500"
  • - Hex / Spanner Size: 20.8 mm / 13/16"
  • - Spark Gap: 1.0 mm / 0.040"
  • - NGK Heat Range: 9
  • - Seat Type: Flat / gasket
  • - Resistor: Yes
  • - Electrode Configuration: Standard / non-projected
  • - Centre Electrode: Nickel alloy with copper core
  • - Ground Electrodes: 1

Compatible Outboard Motors

  • Mercury Outboards
  • - Mercury 7.5 HP – 1979–1985
  • - Mercury 9.8 HP – 1979–1985
  • - Mercury 18 HP – 1980–1983
  • Mercury's application chart lists B9HS-10 as the standard plug and BR9HS-10 as the resistor/suppressor alternative, with a 1.0 mm / 0.040" gap.

Yamaha Outboards

  • - Yamaha 225 / Excel V6 2.6L – 1987–1995
  • - Yamaha 225B 2-Stroke 2596 cc – through 1995
  • - Yamaha 225C 2-Stroke 3130 cc – 1994–2004
  • - Yamaha 225X V6 3.1L – 1994–1999
  • - Yamaha 250B V6 EFI 2-Stroke 3130 cc – 1997–2006

Cross-Reference / OEM Part Numbers

  • - NGK: BR9HS-10
  • - NGK Stock No.: 4551
  • - Mercury / Mariner: 33-813418
  • - NGK B9HS-10: related non-resistor version
  • - NGK Stock No. for B9HS-10: 3626
  • Mercury specifically pairs B9HS-10 / 33-97186 with resistor alternative BR9HS-10 / 33-813418 on the applicable engines.

Important Fitment Information

  • BR9HS-10 is not the same as B9HS-10, BR9HS or BR9ES.
  • - BR9HS-10 – resistor, heat range 9, 12.7 mm reach, 1.0 mm gap
  • - B9HS-10 – non-resistor, heat range 9, 12.7 mm reach, 1.0 mm gap
  • - BR9HS – resistor, heat range 9, 12.7 mm reach, different nominal gap specification
  • - BR9ES – resistor, heat range 9, but 19 mm reach
  • The NGK code means
  • - B – 14 mm thread
  • - R – resistor
  • - 9 – NGK heat range 9
  • - H – 12.7 mm / 1/2" reach
  • - S – standard electrode
  • - -10 – 1.0 mm nominal gap
  • The 12.7 mm reach is critical. Do not substitute the longer 19 mm BR9ES merely because it has the same thread diameter and heat range.

Signs the Spark Plug Needs Replacing

  • - Difficult starting
  • - Rough or unstable idle
  • - Engine misfire
  • - Reduced power
  • - Poor acceleration
  • - Increased fuel consumption
  • - Carbon fouling
  • - Oil fouling
  • - Worn or rounded electrodes
  • - Excessive electrode gap
  • - Corrosion around the shell
  • - Cracked ceramic insulator

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