Cutless Bearing Replacement Discus and W33

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The noticeable +/- 1/32" play in my Discus Cutless bearing was a surprise because it had been replaced professionally six months earlier by the previous owner. The Surveyor suspected engine alignment or rough prop shaft surface.

Prop and Cutless bearing before
                                                                                      Prop and Cutless Bearing Before

Prop Shaft Removal

The Discus and W33 Cutless bearing are of the same design and are basically a larger versions of the Centaur arrangement. The procedure for Cutless bearing replacement is described fully here: Centaur Cutless Bearing Removal and Replacement. More heat may be required to free off the Discus/W33 prop. Hot water wouldn't do it for me but a short application of an oxy-acetylene torch did the trick instantly.

Or use a prop puller like this plate design

Plate puller

Then unscrew the cutless bearing housing using a large pair of stilsons

Prop removed and Cutless bearing unbolted and unscrewed

                                                                                   Cutless Bearing unbolted and unscrewed from shaft tube

To unscrew the cutless bearing housing a large wrench plus a length of scaffold pipe was necessary. I was concerned that the whole shaft tube was rotating so I used a chain wrench inside the boat to hold the shaft tube whilst a colleague lent on the scaffold pipe.

Severe Prop shaft damage!

                                                                                      Severe Prop Shaft Damage - longitudinal slits - evident inside bearing

So new prop shaft and new cutless bearing was indicated. Prop shaft, prop and cutless bearing housing were dispatched to T Norris Ltd in Isleworth for replacement and refurbishment which took about a week. Package arrived back containing new slightly longer prop shaft (to accommodate rope cutter), new cutless bearing fitted to housing with allen key set screws in place of original slotted screws, nicely shiny polished prop and new deep sea seal.

Rudder fouls the prop shaft!

To remove the prop shaft it was necessary to drop the rudder. This was quite straightforward but involved digging an appropriately shaped hole about 3 feet deep and lowering the rudder gently using two ropes looped underneath.

At the same time I took out the prop shaft tube by undoing the clamp at the support inside the boat and feeding it out of the hole left by removing the cutless bearing assembly.

Prop shaft tube clamps just aft of Volvo seal
                                                                       The prop shaft tube clamp is on the aft side of the tube support just behind the Volvo seal in the picture

The new cutless bearing was a nice tight fit to the new prop shaft.

New Cutless bearing fit
New Cutless bearing fit

On the W33 and Discus there is a bronze plate that fits behind the cutless bearing. The lower cutless bearing bolt screws into a hole tapped in the plate whilst the upper bolt has a clearance hole and a nut fixing.

Backing Plate simplifies the lower cutless bearing fixing

I glued the plate in position using black sikkoflex to make relocation easier. Otherwise you may have to use a longer bolt to find the lower hole.

Plate glued in position

In the picture the shaft tube has yet to be replaced. I had to do some reconstruction of the seating of the cutless bearing support both inside and outside of the boat. On the inside a piece of wood that I suppose was used as a former had rotted and was replaced by filled epoxy and on the outside the seat was chipped in places and had to be built up.

I used marine seal on the outside cutless bearing support to boat interface and I put sea cock grease on the threads of the shaft tube to cutless bearing thread. This was not entirely successful as after launch there were drips of water through the thread. This was fixed by loosening the clamp inside the boat and tightening up the shaft tube using a chain wrench on the shaft tube. The drips then reduced and finally stopped.

Update: Replaced cutless bearing last year and used liquid PTFE to seal shaft tube threads. No leak this time.

The completed job

                                                                         Polished Prop, cutless bearing , rope cutter and shaft anode after the job


Cutless Bearing supply and fitting here:

T Norris Marine Isleworth

Trafalgar Yacht Services

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