What size socket is needed for a MerCruiser Bravo 3 prop nut?
I need to take the props off my Bravo 3 outdrive to check for fishing line and grease the splines before the season starts. What size sockets do I actually need to get both the front and rear propellers off?
Answer
To remove the propellers on a MerCruiser Bravo 3 outdrive, you need a standard 1-1/16 inch deep socket for the outer nut and a special 2-3/4 inch socket tool for the inner nut. Because the Bravo 3 uses a twin counter-rotating setup, you cannot do this job without the dedicated inner nut tool, usually MerCruiser part number 91-805457T1.
Required Sockets and Tools
The Bravo 3 outdrive features two propellers on concentric shafts. You must remove two nuts of vastly different sizes.
- Outer propeller nut: This requires a 1-1/16 inch deep socket. A 27mm deep socket fits perfectly if you only carry metric tools. A deep socket is necessary because the inner prop shaft protrudes too far for a standard socket to reach the nut.
- Inner propeller nut: This is a massive 2-3/4 inch hex nut. You need the specific MerCruiser Propeller Nut Wrench (part number 91-805457T1) or an aftermarket equivalent like the Sierra 18-9803. This tool costs around £40 to £60. It features a 1/2 inch square drive hole in the back to accept a breaker bar or torque wrench.
Alongside the sockets, you need a 1/2 inch drive breaker bar, a torque wrench capable of reaching 81 Nm (60 lb-ft), a block of wood, and a tube of marine spline grease.
Removing the Propellers
Always remove the ignition keys and kill cord lanyard before working near propellers. This prevents accidental engine cranking.
Start with the outer propeller. Wedge a block of wood between a blade and the underside of the anti-ventilation plate to stop the shaft from turning. Fit the 1-1/16 inch socket and turn anti-clockwise to break the nut loose. Once the nut is off, slide the rear propeller off the splines. Remove the rear thrust hub sitting behind it.
Move the block of wood to wedge the inner propeller. Slide the 2-3/4 inch special tool over the large inner nut. Insert the 1/2 inch breaker bar into the tool and turn anti-clockwise. This nut is often stubborn due to its size and time spent underwater. Apply steady pressure rather than jerking it. Once removed, slide off the front propeller and the large forward thrust washer.