Renewing Cutlass Bearings
There seems some debate on the correct spelling with Cutless and Cutlass being in common use. Even the manufacturers do not seem to agree on the correct spelling. I have opted for the more common of the two, but should you know the correct version, please let me know.
Cutlass bearings are found in many craft and are often used as propeller shaft bearings. They can be found mounted in the hull structure, in struts to support longer shafts and are sometimes used as rudder shaft bearings. Cutlass bearing construction is basic and the most commonly available type consists of a bronze outer tube, with an inner flexible tube bonded within. The inner tube comes in various materials including rubber, thermoplastic and various synthetic rubbers. The propeller shaft runs within this inner tube. The inner tube is fluted along its length, which allows water to pass through the tube and in doing so lubricates and cools the bearing. The flutes also allow abrasive sand, silt and the like to be flushed out, reducing wear to the bearing surfaces.
Typically these bearings can have a 10 year life expectancy but this will vary with use, shaft alignment and local conditions. A correctly sized bearing on an unworn shaft will exhibit very little movement, if any. Excess movement will cause problems, just as any worn bearing will with rotating parts. Vibration will normally be the first indication of anything amiss but the shaft itself can become worn or even damaged with a badly worn bearing . Excess play within the bearing will mean the transmission is now handling much of the vibration and movement. The picture to the right, shows Â the remains of a worn bearing. It can be seen clearly that this offered very little support with the inner bearing material almost completely worn away.
Where the prop shaft is short. the cutlass bearing can be found mounted within the hull, usually within a bronze housing. Longer shafts are often also supported by a P bracket or strut that contains a cutlass bearing. The majority of these are an interference fit and can be very difficult to remove. A set screw is often used to lock the bearing in place. There are also bearings available that are a sliding fit and require fixing in place by means of adhesive.
It is not always necessary to remove the prop shaft. The interference type may be able to be forced out with brute force and a large hammer, but be careful of damage to surrounding areas. A common method employed is to source a length of pipe with a diameter that matches that of the bearing outer tube. This is cut longitudinally into two ‘shells’. These are taped around the shaft, against the bearing and the big hammer is brought into affect. Do remember to remove any set screws first and be aware there may be more than one fitted. Careful examination of the housing should reveal any lurking beneath anti fouling. A good soaking with WD40 or similar release oil, preferably overnight, will help before attempting removal. Apply through the set screw holes and both ends of the bearing.
The force required to persuade the bearing out of its housing by this method may cause damage to the surrounding area, especially if the bearing to be removed is in a P bracket. A fibreglass hull will not allow the same level of force to be applied as that to a steel hull, so care must be taken. If the bearing is not moving, further persuation will be required.
Removal can be greatly assisted by cutting the bearing along its length. This can be achieved with careful use of a hacksaw. Where access is restricted, an electrical reciprocating saw can be used with great affect. Ideally, cut in alignment with any set screws. Once cut, bolts can be fitting in the set screw hole(s) to assist in lifting the bearing from the housing sides. See below.
Liberal application of freeing oil, careful use of hand tools and some perserverance should see the bearing removed. If the bearing housing is metal, application of heat with a blowlamp can sometimes break the stiction between housing and bearing. If the bearing is still refusing to move, consider further cuts with a saw along the bearing length.
INSTALLING A NEW BEARING
Once you have removed the original, the housing must be completely cleaned. Ensure no trace of corrosion, dirt or adhesive remains. Both hand and power wire brushes work admirably. Any nicks or damage to the bearing mating surface , that may prevent the new bearing fitting, should be gently filed and emery clothed out.
A number of commercial tools are available to allow refitting of cutlass bearings, with some able to be adapted for removal or replacement. Where space permits, a simple threaded rod and suitable washers can be used to great affect. The figure below shows just such an arrangement, with the bearing just entering the P bracket.
great deal of pressure is required here and lubrication of the housing and bearing with soap will ease matters. The tightening nut and washers can bind with friction and applying grease between the washers and along the threads will make the job much easier. If too much force is required when tightening the nut, tapping with a hammer in combination can ease the bearing in, with each few taps being accompanied with a few more turns of the nut.