Cutlass-Bearing Replacement

 The cutlass bearing replacement can either be a horrible experience or one of the easiest jobs below the waterline. The bearing is usually constructed of a heavy rubber or neoprene tube bonded inside a bronze shell. The rubber is fluted to allow the circulation of water to cool and lubricate the shaft. The flutes also flush out silt and sand that can damage the shaft. Its length should be approximately four times the diameter of the propeller shaft. It may be secured to the strut by one or more cone-shaped set screws. Its life expectancy is about 10 years. Replacement is due when the prop shaft starts to shimmy or when the shaft shows movement of about 3/16 of an inch.

 My first experience with a cutlass bearing replacement was a bad one. Fortunately it was on a friend’s boat. Thinking back, I am glad the experience was his, Lord knows I’ve had my share of the bad ones. This was a weekend haulout, paint the bottom, bootstripe, and back into the water. Upon inspection of the prop shaft we found that it was quite loose, so we asked the other do-it-yourselfers who were working in the yard at the time if the cutlass should be replaced and how. We got a different answer from everyone we asked. The favored explanation was, to use a pipe with the same inside diameter as the outside diameter of the shaft. Cut the pipe approximately six-inches long and lengthwise into two halves. The idea was to slide the halves along the shaft up to the strut, and with a hammer drive the bearing out of the strut with the pipe halves. The reason we went with this idea was to save time by not removing the prop shaft. Wrong. After two hours of pounding, the shaft was damaged and the only thing that loosened up and moved was the strut itself. To avoid a damaged shaft, strut, costly lay days, and a horrible experience, the shaft must be removed.

 With the shaft removed and any set screws removed, the strut is now clear at both ends, allowing you to either drive or draw the bearing out of the strut. This is the method that has worked best for me: is take a length of 1/2 inch threaded rod, with a nut and washers on one end that will be small enough to fit inside the strut opening, but large enough to get a good grip on the edges of the bearing. At the other end is another nut, washers, and length of pipe with a diameter larger then the bearing, but small enough to fit on the strut (see Figure 1). The idea with this device is that when you tighten the nut it will draw the bearing out of the strut into the length of pipe.

 A second method of removal may become necessary if the bearing has seized itself to the strut or if you have a boat with a stern-tube bearing that has only one access, usually from the outside. The best technique is to cut a longitudinal cut through the bearing shell with a keyhole saw, trying not to damage the strut or stern tube. With a screwdriver and hammer force the edge of the bearing up to collapse it inward (see Figure 2). This will break it loose and allow it to slide out. Once the bearing begins to move, grab the lifted edge of the bearing with pliers or vice grips and twist it the rest of the way out. With larger bearings a pipe wrench may be needed to twist the bearing out.

 Removing the bearing from a stern tube may be hazardous to your boat’s health. Damage to the stern tube can be easily repaired by inserting the new cutlass bearing part way into the tube to act as a mold, and then reconstruct the damaged area with a two-part epoxy mix or any fairing compound. Remember to use mold wax on the bearing to prevent the epoxy from bonding to the bearing.

 The puller that is used to remove the bearing can be revised to also pull the bearing into the strut. A few larger size washers will be necessary to do the job (see Figure 3). Before installing the new bearing into the strut use a light coating of oil or grease to help ease the bearing into place. Make sure that the bearing and threaded rod is centered to the strut on both ends before tightening the nut to draw the bearing into the strut. Damage may result to the bearing if the threaded rod is not centered. Installing a new bearing into the stern tube is quite simple. Just insert the lightly oiled bearing into the tube and, using a flat piece of wood to protect the bronze shell from damage, tap into place with a hammer. To make the replacement job easier, chill the bearing in ice for several hours before installing, this will contract the bronze shell’s diameter, allowing for easy installation. Do not use dry ice, this will cause the bronze to become brittle and separate the bond between the rubber and bronze shell.

 If you have a set screw to replace, take a drill bit small enough to pass through the existing hole and drill a dimple in the new bearing, this will make a seat for the set screw.

 The pipe, nuts, threaded rod and washers can be bought at any hardware store for a few dollars.

Tools, Hardware and Supplies

Cutlass Bearing (Shaft Bearing)
Pipe Wrench
Channel Pliers
Vice grips
Keyhole saw
Power Drill
Drill Bits
Chisel (steel cutting)
Penetrating Oil
Light oil or grease
Threaded rod

NOTE: Neil Young from England writes:

I feel it might be useful to update your bearing advice as many cutlass bearings these days are machined to be a clearance fit in the bearing carrier.

There are a number of advantages with this approach.

Shaft alignment can be checked as the bearing should spin inside the bearing carrier and on the shaft, when this is possible the bearing is coated in a low temperature epoxy such as Araldite 2011, with the shaft chocked the bearing is inserted. Once the epoxy has hardened chocks are removed and you have an aligned bearing.

The bearing can slide into place by hand no pullers presses required.

Removal is even simpler, the carrier is heated, the epoxy softens and the bearing will slide out.

The old method of interference fits is fast disappearing; also using a puller on an epoxy fitted bearing may not be effective.

Procedure is simple.

1.Chock rear of shaft.

2.Slide bearing up shaft until it enters the bearing carrier (P Bracket/strut)

3.Bearing should slide into bearing carrier easily and it should be possible to spin the bearing.

4.If it sticks or can not be slid into the carrier, adjust alignment of shaft.

5.Slide bearing back out of carrier.

6.Coat with epoxy (we have found that araldite 2011 is the best as it will soften at around 60degrees)

7.Slide bearing into carrier and leave whole assembly still chocked to set.

Shaft is now perfectly aligned in bearing carrier.

To remove no pullers or force is required and there is no corrosion, simply heat the bearing carrier gently, the epoxy will soften and the bearing slides out like its on treacle!

This has proven to be a very effective and easy DIY process for many vessels.

Neil Young