Sierra 18-5431 Rotor Assembly for MerCruiser GM V-8 Thunderbolt IV & V Ignition, Replaces 13524A5

The Sierra 18-5431 Rotor Assembly is a direct-fit distributor rotor engineered for MerCruiser GM V-8 engines equipped with Thunderbolt IV and Thunderbolt V ignition systems. It is built to Sierra's MAGFORCE ignition standards, which are designed to be electronics friendly, protecting onboard electronic devices and engine controls from RFI and EMI interference while still delivering the voltage the ignition system needs to fire reliably. The rotor features moisture-proof, molded distributor insulators and a high-quality conductive center carrier reinforcement that maintains conductor integrity over years of service in the harsh marine environment.

This rotor is confirmed to fit several MerCruiser V-8 engine configurations, including the 500 Bulldog 540/V-8, the 575 540/V-8, and the 800 SC 572/V-8, each identified by specific serial number ranges. It ships as a single-piece rotor assembly and is intended as a direct replacement for the original equipment rotor in these ignition systems, restoring correct spark distribution during a tune-up or ignition system service.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-5431
• Product Type: Rotor Assembly
• Fits: GM V-8 Engines With Thunderbolt IV & V Ignition
• OEM Cross Reference: 13524T1, 13524A5
• Exterior Finish: Machined
• Weight: 0.17 pounds
• Number of Items: 1
• UPC: 030999319302

Fitment

• MerCruiser 500 Bulldog 540/V-8, 1990-2001, serial numbers C577003 - M050281
• MerCruiser 575 540/V-8, 1986-1992, serial numbers A677429 - D763716
• MerCruiser 800 SC 572/V-8, 1993-1998, serial numbers D763836 and up

Replaces (OEM)

• 13524T1
• 13524A5

Frequently Asked Questions

What engines does the Sierra 18-5431 rotor assembly fit? The 18-5431 is designed for GM V-8 engines equipped with Thunderbolt IV and Thunderbolt V ignition systems, and it is confirmed to fit the MerCruiser 500 Bulldog 540/V-8 (1990-2001), the 575 540/V-8 (1986-1992), and the 800 SC 572/V-8 (1993-1998).

Is 18-5431 a direct OEM replacement? Yes, part number 18-5431 is designed as a direct replacement rotor and cross-references to OEM numbers 13524T1 and 13524A5.

How much does the rotor assembly weigh? The Sierra 18-5431 rotor assembly weighs 0.17 pounds.

What does the OEM number 13524A5 correspond to? 13524A5 is one of the OEM cross-reference numbers for the Sierra 18-5431 rotor assembly, along with 13524T1.

How many rotors come in the package? The 18-5431 ships as a single rotor assembly, with one item per package.

What finish does the 18-5431 rotor have? The rotor has a machined exterior finish.

Will the 18-5431 rotor protect onboard electronics from interference? Yes, Sierra's MAGFORCE ignition components, including the 18-5431 rotor, are engineered to be electronics friendly and shield RFI and EMI from onboard electronic devices and engine controls.

Does the 18-5431 rotor fit non-Thunderbolt ignition systems? No, the 18-5431 is specified for GM V-8 engines with Thunderbolt IV and Thunderbolt V ignition systems only.

What serial number range applies to the MerCruiser 800 SC 572/V-8 fitment? For the MerCruiser 800 SC 572/V-8, the Sierra 18-5431 rotor fits engines with serial numbers D763836 and up.

Is the 18-5431 rotor moisture resistant? Yes, the rotor uses moisture-proof, molded distributor insulators to help prevent moisture-related ignition failures in marine use.

What serial numbers apply to the 575 540/V-8 fitment for part 18-5431? On the MerCruiser 575 540/V-8, the 18-5431 rotor fits engines within serial numbers A677429 through D763716.

What is included when I order the 18-5431? Ordering the Sierra 18-5431 includes one rotor assembly; it is sold individually with no additional components.