Spark Plug (NGK D7EA) | Honda CB500K / CB550

Description

NGK D7EA Spark Plug | Honda CB500K / CB550

The NGK D7EA is the correct spark plug for the Honda CB500K, CB550K, and CB550F inline-four engines. Sold individually — you need four plugs per bike.

Why You Need This

The CB500K and CB550 use a different spark plug than the Honda twins. If you’re buying an old CB500 or CB550, there’s no telling what plugs are in there — and just because a plug threads in doesn’t mean it’s the right one. The D7EA is the Honda-specified copper-core plug for these engines. If you’re doing carburetor tuning, keep a few sets on hand to read the plug tip color and gauge your fuel mixture.

Specifications

Gap and Installation

Set the gap to 0.6–0.7 mm (0.024–0.028 in.) using a spark plug gap gauge before installation. Apply a small amount of oil to the threads and hand-tighten until snug.

Terminal nut vs. terminal stud: Each D7EA ships with a terminal nut installed. Unscrew it to expose the terminal stud threads — your spark plug boots connect to the stud, not the nut. It can be extremely tight. See our terminal nut vs. stud guide for details.

Copper-core plugs are ideal for carburetor tuning — keep extras on hand so you can read the mixture on a fresh plug. Light tan to chocolate brown means a healthy fuel mixture.

Frequently Asked Questions

Why won’t my spark plug boot fit on the new plug?

Unscrew the terminal nut on top of the plug to expose the terminal stud. The boots connect to the stud. Use pliers — it can be very tight.

What’s the difference between D7EA and BR8ES?

The D7EA fits Honda inline fours (CB500K, CB550). The BR8ES fits Honda twins (CB350, CB360, CB450, CB500T). They are not interchangeable.

How many plugs do I need?

Four — one per cylinder. The CB500K and CB550 are inline-four engines.

You Might Also Need

• Spark Plug Boots — sold in pairs, available in long and short versions

Last updated: March 2026