RPS Thunderbolt Distributor Cap & Rotor Kit for Mercruiser 5.0–8.2L V8 — Cap, Rotor, Gasket & Screws

RPS Thunderbolt distributor cap and rotor kit replaces worn OEM parts for Mercruiser 5.0, 5.7, 7.4 and 8.2 V8 engines, restoring reliable spark distribution without the OEM price tag.

If your Mercruiser V8 uses a Thunderbolt I or IV ignition system and shows signs of misfires, hard starting or uneven running, a fresh cap-and-rotor kit is a simple, cost-effective service item to renew ignition timing contacts and keep the engine running smoothly. This RPS kit swaps directly for part numbers 805759Q3, 805759T3 and 18-5935 and includes the cap with brass terminals, rotor, gasket and mounting screws so you have everything needed for a clean replacement.

How does this kit fit my Mercruiser engine?

The RPS kit is engineered to match form and function of OEM Thunderbolt distributor caps used on GM-based marine V8 engines from the early 1980s onward. It fits Mercruiser 5.0L, 5.7L, 7.4L and 8.2L V8 applications that accept 805759Q3-style components.

• Direct replacement for part numbers 805759Q3, 805759T3 and 18-5935
• Designed for Thunderbolt I and IV ignition systems
• Compatible with GM-based Mercruiser V8 engines 5.0–8.2 liters
• Includes cap, rotor, gasket and screws for complete installation

What are the materials and build features that matter?

RPS builds the cap with corrosion-resistant brass terminals and a durable insulating shell to resist marine environments and electrical wear. The rotor is molded for accurate contact alignment and the kit supplies a new gasket and fasteners so you avoid seal and mounting issues during replacement.

• Brass terminals for dependable conductivity and corrosion resistance
• High-dielectric insulating cap material to prevent cross-fire
• Precisely molded rotor for accurate spark transfer
• New gasket and screws to ensure a secure, sealed fit

How do I install this distributor cap and rotor kit?

Installation is straightforward for anyone familiar with basic marine engine service. Remove the old cap and rotor, note spark wire positions, fit the new gasket and rotor, then secure the cap with the supplied screws. Verify correct firing order and wire seating before starting the engine.

• Disconnect battery and label spark plug wires before removal
• Replace rotor first, then fit gasket and cap, aligning locator tabs
• Tighten supplied screws to secure cap without over-torquing
• Confirm spark lead orientation and test run at idle after installation

Will this kit improve engine performance or fuel economy?

Replacing worn distributor components restores proper spark delivery timing, which helps the engine run more consistently and can reduce misfires, rough idling or hesitation. This kit renews contact surfaces and sealing, but performance gains depend on overall ignition and fuel system condition.

• Restores clean spark distribution to each cylinder
• Reduces risk of cross-fire and weak sparks from corroded terminals
• Helps stabilize idle and throttle response when ignition parts are worn
• Works best as part of regular ignition and tune-up maintenance

Who is this for: boat owners, marine mechanics and DIYers who maintain GM-based Mercruiser V8 engines (5.0L through 8.2L) with Thunderbolt ignition systems and want an OEM-fit replacement at a lower cost. The RPS kit is suitable for routine tune-ups, preventive maintenance before the boating season, or on-the-water repairs when a worn cap or rotor is causing drivability issues. It offers a complete replacement package—cap, rotor, gasket and screws—so you can complete the job in one stop and get your engine back to dependable operation.