R & D Flexible Shaft Coupling f/4" Yanmar - 3HP/100RPM Capacity

The R & D Flexible Shaft Coupling for 4" Yanmar engines is a precision marine component designed to absorb misalignment and dampen vibration between your engine and propeller shaft. Built from a contoured polyurethane flexible disc, this coupling accommodates the natural flexing of boat structures and engine movement on rubber vibration isolation mounts—critical for maintaining smooth, quiet operation in small to mid-size recreational and fishing vessels.

Rated for 3 horsepower and 100 RPM, this shaft coupling delivers forward thrust through compression on the flexible disc, eliminating the wear and stress that would otherwise transfer directly to your engine bearings and shaft seals. The contoured design provides clearance for bolt heads while allowing the disc to flex freely—absorbing temporary angular and axial misalignment without introducing play or backlash. This design is especially valuable in saltwater environments where engine vibration can accelerate bearing failure and corrosion-related degradation.

Weekend anglers and serious offshore boaters who depend on Yanmar inboard or auxiliary engines benefit from a coupling that extends component life and reduces the telltale vibration that interferes with fish-finding electronics and onboard comfort. If your boat exhibits excessive shaft vibration, unusual bearing noise, or is experiencing premature seal leaks, this OEM-quality coupling replacement restores the dampening characteristics your drivetrain needs. Compact at 8 x 4 x 8 inches and weighing just 2 pounds, it's a straightforward maintenance upgrade that delivers noticeable improvement in overall propulsion system health and longevity.