Mercury – Quicksilver 815921A21 Shift Shaft Bushing Kit | MerCruiser Alpha One Gen II Sterndrives | 815921A21

Overview

Smooth, precise shifting doesn’t just happen — it depends on small parts like this one doing their job. The Quicksilver 815921A21 Shift Shaft Bushing Kit keeps your MerCruiser Alpha One Gen II sterndrive shifting cleanly and reliably by sealing and supporting the shift shaft assembly inside the drive.

Over time, bushings and seals wear down from water exposure and constant motion, leading to sloppy shifting or leaks. This OEM kit replaces everything you need in one go, restoring that factory feel when you move the throttle from neutral to forward or reverse.

Key Features

• Purpose: Replaces worn or leaking bushings and seals in the shift shaft assembly for smooth, accurate shifting.
• Fitment: Designed specifically for MerCruiser Alpha One Gen II sterndrives.
• Kit Contents: Includes housing pieces, seals, and zip tie — a complete five-piece OEM replacement set.
• Build Quality: Made from marine-grade materials to resist corrosion, heat, and saltwater wear.
• OEM Precision: Built to Mercury Marine factory specs for proper fit, sealing, and long-term reliability.

Engine & Boat Compatibility

• Compatible with MerCruiser Alpha One Gen II sterndrives
• Common on cruisers, bowriders, fishing boats, and performance rigs using MerCruiser power

Performance & Practical Benefits

The 815921A21 kit takes the play out of worn shift components and restores that crisp, confident feel when engaging gears. A proper seal around the shaft also keeps water out and gear lube in — critical for avoiding internal corrosion and costly lower unit damage.

Each piece in the kit is engineered to hold up to marine abuse — temperature swings, vibration, and repeated gear changes. The materials maintain their shape and sealing ability even after long hours of use. With this OEM set, you’ll get back the solid, precise shifting that makes Mercury drives so dependable.

Why Buy OEM

When it comes to shift components, tolerances matter. Mercury’s OEM kits are made to the exact dimensions and materials required for a tight, leak-free fit. Aftermarket kits often cut corners with softer plastics or seals that don’t quite align, leading to premature wear or gearcase leaks.

By using genuine Quicksilver parts, you’re putting the same components back into your drive that Mercury installs from the factory. It’s the simplest way to make sure your sterndrive shifts cleanly and stays protected from water intrusion.

FAQ

Q1: What drives does the Quicksilver 815921A21 kit fit?
A: It’s made for MerCruiser Alpha One Gen II sterndrives.

Q2: What’s included in the kit?
A: The kit comes with housing pieces, seals, and a zip tie — five parts total.

Q3: What does this kit fix?
A: It replaces worn shift shaft bushings and seals that can cause loose or stiff shifting and potential oil leaks.

Q4: Can I install it myself?
A: Yes. If you’re comfortable working with your sterndrive’s shift system, installation is straightforward with the right tools and a service manual.

Q5: Why choose Quicksilver OEM over aftermarket?
A: OEM kits ensure a perfect fit, better sealing, and proven durability — keeping your drive reliable for the long haul.