Autolite 4275 Spark Plug

Overview

Autolite 4275 is a copper non-resistor spark plug built with OE form, fit, and function in mind. It is listed for Harley-Davidson Shovel Head applications and uses a copper center electrode with nickel ground and center tip materials for consistent ignition performance.

Key Features

• Copper center electrode for responsive ignition performance.
• Non-resistor design for applications that call for a no-resistance plug.
• Tapered ground electrode tip and standard regular center electrode design.
• Mid-projection ceramic insulator with a flat seat and removable nut terminal.
• 14.0 mm thread diameter, 0.374 in reach, and 13/16 in hex size.

Detailed Description

Autolite 4275 is engineered as an OE-style replacement spark plug for classic Harley-Davidson motorcycles, including FL, FLF, FLFB, FLHB, FLHFB, FLHF, FX Super Glide, FXE Super Glide, and FLH Electra Glide applications. The copper core helps support quick starts, smooth acceleration, and improved fuel economy, while the nickel electrode materials and mid-projection insulator support stable spark delivery in the specified applications. This part number, 4275, is also cross-referenced to Monroe Shocks & Struts 172286 and 182286 for the same application.

What It Is Used For

• Restoring ignition performance when the original plug is worn or fouled.
• Addressing hard starting caused by degraded spark delivery.
• Reducing misfire symptoms tied to plug wear or incorrect plug type.
• Supporting smoother throttle response in specified Harley-Davidson Shovel Head engines.

Installation Notes and Tips

Verify thread diameter, reach, seat type, and terminal style before installation. This plug is specified with a 0.034 in pre-gap, so confirm the gap against the engine’s requirements before use. Fitment includes 1947-1974 Harley-Davidson FL, FLF, FLFB, FLHB, FLHFB, FLHF, FX Super Glide, and FXE Super Glide applications, with notes calling out Shovel Head coverage and a .025 in / 0.6 mm specification in the fitment data.

Quality Assurance

Autolite is a long-standing supplier of spark plugs to the automotive aftermarket and original equipment manufacturers, and this part is built to OE form, fit, and function standards for the listed applications.