NGK Spark Plug – CR5EH-9

The NGK CR5EH-9 is a standard copper-core nickel spark plug used in select small four-stroke marine outboards, utility engines, generators, pumps, and compact power equipment where the manufacturer specifies the CR5EH-9 / NGK 6689 plug profile. It uses a compact 10 mm shell, resistor construction, partial-thread long-reach layout, and factory 0.9 mm / 0.036 in. gap for compatible engines that require this specific plug design.

This plug should be installed only where the engine service manual, equipment label, or factory application chart specifically calls for NGK CR5EH-9, NGK 6689, or an approved equivalent.

Key Features

• Genuine NGK standard spark plug.
• NGK part number: CR5EH-9.
• NGK stock number: 6689.
• Copper-core nickel construction for standard service applications.
• Built-in resistor to help reduce ignition-related RFI noise.
• Compact 10 mm plug body for small-engine cylinder heads.
• Partial-thread / half-thread style reach layout.
• Thread diameter: 10 mm / M10 x 1.0.
• Total reach: 19 mm / 3/4 in.
• Threaded portion reference: 12.7 mm / 1/2 in.
• Hex size: 16 mm / 5/8 in.
• Heat range: 5.
• Factory preset gap: 0.036 in. / 0.9 mm.
• Terminal style: threaded stud.

Application Compatibility

Common application context includes select marine and utility engines where the factory plug chart calls for NGK CR5EH-9 / 6689, including:

• Select Honda BF8D FourStroke outboard applications where specified
• Select Honda BFP8D high-thrust outboard applications where specified
• Select Honda BF9.9D / BFP9.9D FourStroke outboard applications where specified
• Select Honda BF15D / BFP15D FourStroke outboard applications where specified
• Select Honda BF20D / BFP20D FourStroke outboard applications where specified
• Select compact generator, pump, and industrial small-engine applications requiring the same 10 mm partial-thread plug profile

Use this spark plug only where the manufacturer’s application chart specifically lists CR5EH-9, 6689, or an approved equivalent.

Fitment Notice

Confirm fitment by exact engine model, serial number, model year, service manual, and factory spark plug chart before ordering. Spark plugs with the same 10 mm thread diameter can still differ in reach, thread length, heat range, seat style, terminal type, resistor specification, projection, 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, corroded, cracked, damaged, or causing hard starting, rough idle, weak acceleration, misfire, poor low-speed running, or no-start conditions. Small four-stroke outboards and utility engines that idle for long periods, troll at low speed, or sit in seasonal storage should have 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. Avoid adding anti-seize unless the engine or spark plug manufacturer specifically calls for it, as lubricant can change clamping load and increase the risk of over-tightening in small aluminum cylinder heads.

For 10 mm plugs in small aluminum cylinder heads, use a torque wrench and follow the engine manufacturer’s exact specification. Do not force the plug if resistance is felt; stop and inspect the threads before continuing.

Alternate/Superseded Part Numbers

• NGK CR5EH-9 spark plug part number
• NGK 6689 NGK stock number
• CR5EH9 alternate catalog formatting
• Honda 98059-55916 cross-reference; verify by engine model and plug chart
• Honda 98059-55926 Honda reference; verify by engine model and plug chart
• Denso U16FER-9 / U16FER9 cross-reference; verify by application

Parts Desk Insight

The CR5EH-9 should not be substituted by thread size alone. Its partial-thread reach layout is application-specific, and the wrong 10 mm plug can seat incorrectly or place the firing end at the wrong depth in the chamber. Matching the exact plug number, gap, terminal style, and service chart helps prevent ignition issues and protects small aluminum cylinder heads.

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