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Post by wolfram on Apr 19, 2022 15:53:47 GMT
Another one for you to all ponder!
Have recently removed stern tube, shaft, cutlass bearing etc to reseal the stern tube. All going well until....
Upon attempting a dry fit with new cutlass bearing and stern tube, it seems that the p bracket is not concentric to the stern tube.
The shaft needs to be pulled down forward of the p bracket in order to enter the stern tube centrally. Is this normal?
I removed the sealant around the p bracket to reseal, no damage internally or externally, absolutely no movement in the bracket at all and there was no untoward vibration previously. Old cutlass showed signs of wear.
I'm thinking it's either an issue with the layup of the vessel in the yard, and the hull has deformed whilst sat on its keel, or its poor alignment from build.
P bracket does appear to run slightly to port of keel, but believe this to be normal to allow removal of shaft with rudder in place?
Anyone got any experience?
Ta
Alex
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Post by Charlie-Bravo on Apr 19, 2022 17:46:04 GMT
Hi, a question springs to mind, .... when were the engine mounts last renewed?
Given the P bracket is more or less a fixed position, and the gearbox flange ..... a slightly adjustable position, once new engine mounts have established themselves, the stern tube can then be fixed in a floating position in between. If the angle of the P bracket isn't good, shim it to a better position to point it at the reliably positioned gearbox flange ( a 90deg laser off amazon is handy) , ...... Hope that helps a little.
Boats do change shape over the years, so go with what you have and re engineer it to work, but do check the engine alignment.
CB
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Post by wolfram on Apr 19, 2022 18:49:28 GMT
Hi CB,
Thanks for the reply.
I doubt the mounts have ever been renewed I'll take a good look at them when I get back to the boat on Friday with a view to replacing, seems prudent given the efforts so far.
I think what is concerning me is how the shaft is sitting in the cutlass when offered up for the stern tube, its sitting very "flat", compressing the forward lower and aft upper side of the cutlass bearing if that makes sense.
I've only got experience with saildrive and the compression of these areas in the cutlass seems a tad dramatic to me!
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Post by Charlie-Bravo on Apr 19, 2022 19:41:51 GMT
As already suggested, re engineer it as best as you can, then it won't cause future issues, you seem to have a grip on how it should be.
Engine mounts available from Parts4engines ( google it) a bit cheaper than many others.
CB
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Post by Charlie-Bravo on Apr 19, 2022 20:20:50 GMT
"I think what is concerning me is how the shaft is sitting in the cutlass when offered up for the stern tube, its sitting very "flat", compressing the forward lower and aft upper side"
Dont forget to take into account the weight of the shaft( if you haven't already), as that will flex the P bracket to hull joint, and may look worse than it is, it has a fair amount of leverage, and would look as you describe.
It is tricky to allow for the shaft weight to any degree of accuracy, ......... a test of your ingenuity perhaps.
CB
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Post by wolfram on Apr 19, 2022 20:40:35 GMT
Thanks CB,
Will let you know how it goes!
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Post by rene460 on Apr 20, 2022 10:26:56 GMT
Hi Wolfram,
It is worth looking at the problem from the other end before you change too much.
You have said that there was no sign of looseness or movement of the P bracket, so in all likely hood it is still in exactly the same position as before you lifted the boat. Remember the hulls all bend a bit when on the hard, and the floatation forces which are somewhat distributed along the hull as dictated by the shape, are replaced by a solid support under the keel plus some props at each end, while the rigging tension is still being applied. These supports do result in some longitudinal bending, which is why the conventional advice is to only do final alignment when afloat. When you launch, and the normal buoyancy forces on the hull return, the stern will almost certainly move up relative to the engine location, which if I have understood you correctly, would “flatten” the shaft as required.
As CB has said, it is very difficult to predict, and I find that it is always too late when I realise that I should have observed carefully how things line up when first on the hard before any other work. But a good guess is that if the alignment was correct before lift out, it will return to that position. So have a good look and consider whether there is any reason why this would not be so. I think in an ideal world, we would all recheck our shaft alignment after launching, but from what I can gather, most of us don’t, we leave things until we notice vibration or excessive cutlass bearing wear.
The shaft seal is not supposed to be supporting the shaft and is mounted with a little flexibility so it can move to centralise the seal on the shaft. The shaft is actually an extension to the engine crankshaft, connected by a rigid flanged coupling at the engine end. Only supported by the cutlass bearing the shaft is not well supported and the end forest from the bearing will drop, and the shaft will bend a little under its own weight. I assume the propellor is still not installed. As you have noted the P bracket is not adjustable, so the engine has to be aligned to point the shaft so it is a straight line continuation of the crankshaft to the centre of the cutlass bearing. You can’t see each end when afloat, and the shaft is relatively flexible, unlike the engine block, so the engine is normally aligned by adjusting the mounts so the two parts of the flanged coupling are exactly parallel. This is a skilled job with feeler gauges, not a steel ruler. Mounts generally last a long time, so unless there was signs of them failing before, probably no need to replace them, but it’s a judgement to be made on how the engine is sitting, and how it moves when the engine is operating.
When the shaft is in the cutlass bearing and the motor end loosely connected, the shaft should be approximately in the centre of the shaft tube in the hull before you instal the seal. If the new tube dotted reasonably in the hole left by the old one, it should be pretty much in the right place, but not necessarily exactly.
You mentioned that the old cutlass bearing was a bit worn. I would suggest that this indicates that the shaft needed re-alignment before you started, but I gather from your words that it was not bad, so just re-check when back the water. And before you get the shaft aligned, in the water, do check that you are happy with your rig tension as that also applies bending forces to the hull so can also affect the alignment.
I hope that is not too confusing.
Rene460
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Post by fma on Apr 20, 2022 12:19:59 GMT
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