Sierra Timer Base 18-99440 for Johnson/Evinrude 3-Cylinder Outboards, Replaces 133-1251, 580970, 581251

The Sierra 18-99440 is a timer base built for Johnson/Evinrude 3-cylinder outboard engines, a core component of the ignition system that controls spark timing as the engine runs through its RPM range. It is constructed of marine-grade materials to hold up to the vibration, heat, and moisture typical of an outboard powerhead environment. The timer base is designed for straightforward removal-and-replacement service, making it a practical choice when an original timer base has worn out, cracked, or is no longer advancing timing correctly.

This timer base is intended for Johnson and Evinrude 3-cylinder Cross Flow outboards, including 65HP, 70HP, and 75HP models as detailed in the fitment section below. It directly replaces several factory and aftermarket part numbers, so it can be used as a like-for-like swap on engines originally equipped with any of those numbers. Buyers replacing a failing timer base should confirm their engine's horsepower rating and model designation against the fitment list before ordering.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-99440
• Weight: 0.4 pounds
• Material: Marine-grade materials
• Color: Blue
• Cylinder Configuration: 3 Cylinder
• Compatible Engine Brand: Johnson/Evinrude
• UPC: 808282394806

Fitment

• Johnson/Evinrude 65HP Cross Flow (1972-1973)
• Johnson/Evinrude 70HP Cross Flow (1974-1978)
• Johnson/Evinrude 75HP ES ER EL Cross Flow (1975-1977)
• Johnson/Evinrude 75HP ER EL Cross Flow (1976-1978)

Replaces (OEM)

• 133-1251
• 580970
• 581251

Frequently Asked Questions

What engines does the Sierra 18-99440 timer base fit? The Sierra 18-99440 timer base fits Johnson/Evinrude 3-cylinder Cross Flow outboards: 65HP (1972-1973), 70HP (1974-1978), 75HP ES ER EL (1975-1977), and 75HP ER EL (1976-1978).

Is the Sierra 18-99440 a direct replacement for the original timer base? Yes, the 18-99440 is designed as a direct replacement for the timer base on the listed Johnson/Evinrude 3-cylinder Cross Flow engines, replacing OEM/aftermarket numbers 133-1251, 580970, and 581251.

What OEM part numbers does 18-99440 cross-reference? The Sierra 18-99440 timer base replaces part numbers 133-1251, 580970, and 581251.

What is the Sierra 18-99440 timer base made of? It is constructed of marine-grade materials suited to the heat, vibration, and moisture exposure inside an outboard powerhead.

How much does the Sierra 18-99440 timer base weigh? The Sierra 18-99440 timer base weighs 0.4 pounds.

What color is the 18-99440 timer base? The 18-99440 timer base is blue.

Will this timer base work on a 2-cylinder or 4-cylinder Johnson/Evinrude engine? No, the Sierra 18-99440 is built specifically for Johnson/Evinrude 3-cylinder engines and is not intended for 2-cylinder or 4-cylinder applications.

Does the 18-99440 fit both Johnson and Evinrude outboards? Yes, since Johnson and Evinrude 3-cylinder Cross Flow outboards share ignition components, the 18-99440 timer base fits the applicable models from both brands.

Can I use the 18-99440 on a 75HP outboard? Yes, the 18-99440 fits 75HP ES ER EL Cross Flow (1975-1977) and 75HP ER EL Cross Flow (1976-1978) Johnson/Evinrude engines.

Why would I need to replace a timer base? A timer base controls ignition spark timing as engine RPM changes; the Sierra 18-99440 is used to replace a worn, cracked, or malfunctioning original timer base to restore correct timing operation.

Is the 18-99440 timer base genuine Sierra or a generic part? The 18-99440 is a Sierra-branded timer base manufactured to replace the listed Johnson/Evinrude OEM and aftermarket timer base numbers.