Prop shaft straightness

[SimonD]

It can also be that the hole is not central in the coupling. Try the broomstick method (carefully!) or better use a dial gauge, but move it as far forward as possible, then as far aft for comparison. Sometimes moving the coupling round 90 degrees on its bolts will help.

Thanks Vyv. I've never heard of the hole not being centred. If I could get some sensible indication of 'wobble' I could then, as you say, move the coupling 90 degrees and compare measurements. As the boat is out of the water, this measurement will have to be done by rotating the shaft manually. That said, it should give the same result.

Whilst we're delving into this, I should mention that the shaft looks central in the cutlass bearing, but certainly not central in the stern tube (when viewed from the outside). It looks closer to the port side of the tube than the starboard, but central at top and bottom. I'll need to look at the shaft as it exits the stern tube on the inside when I've removed the gland seal. If it's not central, I'm not sure where to go next. The implication that the engine needs to move to starboard is too awful to contemplate! Some means of checking the shaft is concentric with the coupling would be handy, but I'll check the shaft runout first.

 

[Tranona]

That could well be the problem. Although the Volvo seal is fairly supportive, it is important to ensure that the shaft is centred in the tube before aligning the engine with the coupling so that the shaft and the cutless are in a straight line. However if this is not aligned properly it is likely that the cutless wears on one side.

 

[SimonD]

That could well be the problem. Although the Volvo seal is fairly supportive, it is important to ensure that the shaft is centred in the tube before aligning the engine with the coupling so that the shaft and the cutless are in a straight line. However if this is not aligned properly it is likely that the cutless wears on one side.

Umm. Assuming that the P bracket was correctly installed in the first place, the cutlass bearing should be concentric with the stern tube. In that case, it would seem sensible to disconnect the shaft from the coupling and slide it back until it's free. Then centre the shaft in the stern tube and check it lines up with the coupling. Any significant misalignment should be fairly obvious and, if it's left to right rather than up and down (crudely put) then it means the engine could need shoving over. Does that sound about right?

 

[danielefua]

Umm. Assuming that the P bracket was correctly installed in the first place, the cutlass bearing should be concentric with the stern tube. In that case, it would seem sensible to disconnect the shaft from the coupling and slide it back until it's free. Then centre the shaft in the stern tube and check it lines up with the coupling. Any significant misalignment should be fairly obvious and, if it's left to right rather than up and down (crudely put) then it means the engine could need shoving over. Does that sound about right?

The displacement of the engine from the correct position could be the initial cause of the bending of the shaft which, in turn (maybe in this case I should write "turning"!), produces the wobble. The displacement itself does not produce a wobble.
It looks like you have several things to check... Good luck!

Daniel

 

[SimonD]

I'm beginning to wonder if it wouldn't be easier to convert to a saildrive....

I'll take on board the tips and check through everything.

 

[xeitosaphil]

Umm. Assuming that the P bracket was correctly installed in the first place, the cutlass bearing should be concentric with the stern tube. In that case, it would seem sensible to disconnect the shaft from the coupling and slide it back until it's free. Then centre the shaft in the stern tube and check it lines up with the coupling. Any significant misalignment should be fairly obvious and, if it's left to right rather than up and down (crudely put) then it means the engine could need shoving over. Does that sound about right?

This is what I was referring to in Post 10, there is no point trying to start in the middle of the re- alignment task, you have to start at the beginning and check that every step is correct along the way. There are really no short cuts.

What I did forget to mention though, is that when the shaft was removed and checked for true, and the Cutless Bearing was replaced ( as I didn't want to chance there was any wear in it once the whole thing was back together,for the sake of £20 ) I centred the shaft in the stern tube on the inside, before the engine shaft alignment started. This is where the need to re adjust the engine mountings came in.
Once the cutless bearing was renewed and installed and the shaft was centred and fixed in the stern tube at the inside inboard end , the engine needs to be aligned to the shaft, to the tolerances quoted.

The only way I could centre my shaft in the tube was to measure the inside diameter of the stern tube with a vernier gauge, and subtract the shaft diameter from that. The difference in measurement, then divided by two is the clearance all round the shaft.

In my case it was only 2.1mm?

The only way I could think of setting that clearance was, with a series of 2.1mm drill bits which I taped all the way around the shaft and inserted into the stern tube, which fixed the shaft in the centre of the tube while the engine alignment took place. The other thing you need to do is put the stern gland on the shaft before you do the final adjustment .Once adjusted, just slide the gland back onto the stern tube fix clips, job done.

To complete the task you need to get your prop checked for balance, I was lucky in that I replaced mine two blade with a Darglow Featherstream so didn't have to worry.

As you said before it does take patience unfortunately, but good engine alignment takes time and I don't think there are any short cuts, and you should not take anything as being ok unless you check it out for your self.

Only my opinion of course.

Best of luck with yours

Philip

 

[SimonD]

Thanks Philip, that's really helpful. Sorry I wasn't paying attention at the back of the class earlier!

Once I've checked the shaft is true, I'll follow your method (although I hope to find more than 2.1mm clearance!). I also hope to find that the engine doesn't need any sideways movement. If it does, I'll be calling in the professionals.

I'll report back in the New Year.