Cutlass Bearing Maintenance: Spotting Wear and Replacing It Safely

Maintaining the integrity of your boat's propulsion system is crucial for smooth operation and the cutlass bearing plays a vital role in that process. Over time, wear and tear may necessitate replacing this part. In this guide, we’ll explore what a cutlass bearing is, how it functions and how to determine when it needs replacement. We'll also provide a step-by-step guide for changing a cutlass bearing on your boat. 

What Is a Cutlass Bearing? 

A cutlass bearing is a cylindrical component that supports the propeller shaft and allows it to rotate smoothly. It's typically located inside the P or A bracket, and/or sterntube. 

Made from brass or composite material with a rubber inner lining, the bearing allows for water lubrication. The grooves in the rubber facilitate the flow of water, which serves both to cool the bearing and to reduce friction, enabling the shaft to rotate freely. 

Key Functions of a Cutlass Bearing: 

• Support: It holds the propeller shaft in place, preventing excessive movement that could cause misalignment. 

• Lubrication: The grooves in the bearing's rubber lining use water to lubricate the shaft and maintain smooth rotation. 

• Wear protection: It absorbs the wear from the shaft's movement and keeps the propeller from becoming misaligned, protecting other components. 

How to Identify if a Cutlass Bearing Needs Replacing 

Like any mechanical part, cutlass bearings wear out over time. Regular inspections are key to identifying when it needs replacing. Signs that indicate it’s time for a new bearing include: 

• Excessive play in the shaft: If you can move the propeller shaft up and down or side to side when the boat is out of the water, the bearing is likely worn out. The movement should be minimal. 

• Noise or vibration: Unusual noise or excessive vibration while the boat is in motion can signal that the bearing is failing. 

• Visible wear or deterioration: Inspect the bearing for cracks, distortion or significant wear. If the rubber lining is visibly worn down, it’s time for a replacement. 

• Increased shaft resistance: A worn bearing may cause the shaft to turn with more resistance than usual, indicating higher friction and less effective lubrication. 

Tools and Materials You'll Need: 

• Propeller puller or shaft coupling tool 

• Bearing puller or homemade bearing extractor 

• Hammer and chisel 

• Hacksaw 

• Vice grip pliers 

• Replacement cutlass bearing 

• Lubricant (water or grease, as recommended) 

• Allen keys or wrenches 

• Thread locker (if necessary) 

• Marine-grade sealant (optional) 

Step-by-Step Guide to Replacing a Cutlass Bearing 

1. Prepare the boat 

Before starting, the boat needs to be out of the water. You should have access to the propeller shaft. Make sure the boat is securely placed on stands or supports. 

2. Remove the propeller and shaft 

To access the cutlass bearing, the propeller needs to be removed. Use a propeller puller to carefully detach the propeller from the shaft. Be sure to store the propeller and all fastenings in a safe place.  Once the propeller is removed, you can go ahead and draw the shaft by disconnecting it from the coupling. 

3. Extract the old cutlass bearing 

With everything out the way it’s time to turn your attention to extracting the old cutlass bearing.  This is usually the most difficult part of the job. There are a few methods to doing this depending on your stern gear arrangement.  Generally, with P & A brackets, along with a stern tube with the bearing aft of the keel, there will be grub screw that needs to be located prior to extracting the cutlass bearing.  These are used to stop the bearing rotating, rather than securing them in place.   

To remove the old bearing, you can use a bearing puller designed for the task, or you can fashion a homemade extractor using threaded rods, plates and nuts. Another option is to use a hacksaw and make a cut all the way through the bearing, taking care not to damage the surrounding casing.  Once cut, carefully use hammer and chisel/screwdriver to carefully knock the old bearing out, although this method can risk damage to the strut.  With some particularly stubborn bearings, if the cut is made just below the grub screw holes, bolts can be inserted to help move the bearing away from the outer casing.  

Tip: Be patient and work slowly to avoid damaging the housing. 

4. Clean the housing 

Once the bearing is removed, clean the inside of the strut thoroughly. Any debris or corrosion left behind can affect the installation of the new bearing and the performance of the shaft. 

5. Install the new cutlass bearing 

Coat the new cutlass bearing with a light lubricant (if recommended by the manufacturer). Position the new bearing into the strut and gently tap it into place using a bearing press or a mallet. Be careful to ensure that it goes in straight and does not get misaligned during installation. The bearing should be installed with the landed area positioned at the bottom to prevent damage during start-up. Once correctly in position, reinstall the grub screws. 

Tip: Avoid using excessive force, as it could damage the new bearing or the strut. 

6. Reinstall the Propeller 

Once the bearing is properly seated, reinstall the propeller and shaft. Ensure that the propeller is firmly attached and that all fastenings are secure, using a thread locker if necessary to prevent vibration-related loosening.  It can be beneficial to cool be bearing prior to reinstallation, a few hours in the freezer will be enough. 

7. Test the Installation 

Before putting the boat back in the water, check for any remaining play in the shaft. Rotate the shaft by hand to ensure it spins freely without friction or noise. Once you're satisfied, you can safely return the boat to the water. 

Maintenance Tips to Extend the Life of Your Cutlass Bearing 

• Regular inspections: Check for excessive play in the shaft or signs of wear during routine maintenance. 

• Keep the shaft aligned: Misalignment can put undue stress on the bearing, causing it to wear out faster. 

• Flush with water: Keeping the bearing lubricated with clean water will reduce friction and extend its life. 

• Check for marine growth: Barnacles and other growth can reduce water flow through the bearing, so ensure the area around the strut is kept clear. 

Changing a cutlass bearing can be a challenging task, but with the right tools and a clear understanding of the process, it’s manageable for most boat owners. Regular maintenance and timely replacement of this crucial part will help keep your boat running smoothly, protecting both the propeller shaft and engine from damage. 

This guide should provide you with the knowledge you need to maintain and replace your cutlass bearing effectively. If you're comfortable with handling the tools, replacing a cutlass bearing is a great way to save on boatyard labour costs and ensure a job well done.