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Alan and Debbie
Apr 11, 2010 - 8:10PM
Stern Gear and Prop Shaft
What a saga! Just back from a week refitting which included fitting an Ambassador rope stripper. This meant shortening the stub of the cutlass bearing so decided to replace it anyway. Decided to loosen the prop before splitting the shaft, so started by cleaning up the prop nut and removing the split pin it came out nice and cleanly. Loosened off the nut with a big wrench and a little heat, no problem at all. Applied my patent puller to the prop and with a lot of pressure, a little heat and a wack with my big copper hammer, off it came. Took out the centre shaft to allow me to draw the shaft in and attack the old cutlass bearing . Horrors, when I drew the shaft in I found out why my stuffing gland would never seal very well. The shaft was like a cheese grater with pitting 2mm deep in places! We had no choice but to replace it so I fabricated a press out of two thicknesses of 10mm steel bar, got the nut off the inner flange of the rear shaft and applied huge pressure with two HT steel bolts to the flange. Even with heat and a judicious wack or two it would not budge. I was a bit surprised that the shaft could not be drawn inwards and out with the flange in place, especially as there was only millimetres in it. But as the shaft was being replaced anyway I pulled it back as far as possible and cut it in two which allowed me to get it out in two halves. It eventually took a hydraulic press in the workshop to separate the inner flange from the shaft! There is no way that it would have been separated in the confines of the rear bilge. So, off to the engineers with the two halves and they made me a very nice new shaft machined at each end for the flange and the prop, I left both of these with them to ensure a proper fit. A word of warning though. The engineer refitted the inner flange with a metric nyloc nut and a thicker washer because he found that the original thin washer was badly crushed into the hollow of the flange. The engineer did what he thought was best but when I trial fitted it to the centre shaft and silent bloc I found that it fouled the centre shaft because of it’s extra 5mm or so. Easy we thought, shorten the shaft and the nut, trouble was that this left a short nut with no nyloc. I settled for a compromise on the washer thickness, a nut with no nyloc and drilled the nut and shaft insitu to take a split pin for added security. Interestingly the original imperial nut with the traditional split end lock was hardly benefiting from the split lock in any case because it was fitted short. Another point here, the engineer had mistakenly fitted the inner flange to the shaft and had tightened it down. I found that this had distorted the thread sufficiently to mean that I could not easily spin the nut on as I wanted to be able to, so I had him remake the thread. The old cutlass bearing came out fairly easily because of the pinch bolt stern gear and a good stub out of the gear. Any way, at the end of the day it all went together very well and I re-packed the stuffing gland with far more confidence that it wouldn’t leak so much. Fitting the Ambassador then took about an hour! Beautifully engineered piece of kit I am very happy with it so far and actually still have nine and a half fingers left. I have some pics of the old shaft and the overall process which I will put on the gallery soon. Postscript though, I think our shaft suffered so badly because Ken the previous owner had lived aboard connected to shore power for 12 years. I don’t think it is a general problem – unless your stuffing gland won’t seal whatever you try!
SeaDog Name (if owner or crew) Star Dog
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John Lansdell
Apr 11, 2010 - 10:34PM
Re: Stern Gear and Prop Shaft
Our shaft was in the same condition with a many pitted areas on it. Howver, ours came to pieces without the problems you have had. We had a new one made. Rightly or wrongly I have fitted a greasing point on the stern gland. Before and after each trip I squirt some grease into the gland. One side benefit is virtually no drips into the bilge when she is not in use.
SeaDog Name (if owner or crew) Twotails
E Richardson
Apr 12, 2010 - 3:33PM
Re: Stern Gear and Prop Shaft
Hi Alan & Debbie
The corrosion problem you report is exactly what I found when I first had Taliesin. The fact that it had occured within the packing area was due to the use of graphite packing at some time. Back in the 70s & 80s it was very popular and most boatyards used it. With Graphite being quite a nobel substance the prop shaft suffers badly.
The corrosion looked just as though worms had eaten the shaft surface.
You will not get that with your new packing.
It is important to have a good electrical bond across the coupling joints and if possible an earthing brush fitted to the shaft and grounded to your anode.
Eric
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