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Prop shaft off centre


  • This topic has 7 replies, 4 voices, and was last updated 2 years ago by Anonymous.
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    Nicholas Muir

    I have noted that the prop shaft is not positioned in the middle of the bronze tube, rather offset to one side and almost touching the lower side of the tube. (see attached photo). There is no play in the cutlass bearing and to correct the position to the centre would mean lifting the engine up about 15mm (quite a lot) – this would then mean the cutlass would potentially not be aligned with the angle of the prop shaft. Is this just how it is, and it was built like this or should the prop shaft run through the centre of the tube?
    Note that the prop shaft has been like this for some time without any issues.


    Interesting discovery! Naturally when constructed it should have been in the centre at both ends of the stern tube. First question is – is it in a similar position on the inboard end? That’s difficult to tell without disturbing the water seal. Until you know the answer you can’t just “lift the engine” you really are governed in the alignment of the the cutlass and P bracket now it is where it is – if say the inboard end of the shaft is at the top of the hole raising the engine would make it rub on the hull! It does raise a lot of issues but if it’s been like it since you have owned her I would leave well alone. To me it looks misaligned from new unless the P bracket has been re set for some reason. Do I detect a wear mark on the shaft where it is close to the hull?

    Nicholas Muir

    Thanks Dick
    It has been like this since I acquired her, so I think it is really a matter of leave well alone, as you recommend. There is no evidence that the prop shaft is rubbing on the tube through the hull. As you say, it is probably not easy to examine the inboard end of the tube.
    Thanks again. I shall await any other suggestions


    Same happen to me. Replaced engine mountings and fixed. Also had some vibration problems when forward idle. If your mountings are ok you can lift the engine a bit.

    Nicholas Muir

    Thanks for that. Feels like something that I should ask a shipwright to look at and fix.


    Altering the engine alignment without taking other fixings into consideration (P bracket) you could end up with issues elsewhere – engineer opinion is a good idea

    Nicholas Muir

    Had response below from Roderick Barry outside this thread.
    Hi Nicholas, More than likely the shaft would have started life centred in the tube as this allows for movement. The shaft and cutlass bearing would have been lined up true when the boat was built. With the shaft off centre will mean they are no longer aligned and wear will be induced in the cutlass bearing/shaft. Firstly is the prop shaft running true if you rotate it by hand. By this I mean if you rotate it does it stay as in the position shown in your picture or does it move relative to the hole. If it moves relative to the hole something is wrong. Possibly the coupling to the gear box or the shaft is bent but this needs investigating. I hope both these are long shots. If it stays in the same place relative to the hole it is most likely your engine mounts have gone soft / settled over time and shaft realignment is required, this is quite normal. Don’t just jack up the back of the engine to bring the shaft back to the centre a full realignment is necessary and there are NO shortcuts. Hope this helps best regards, Rod.”

    Nicholas Muir

    Thanks very much for your advice Rod. The shaft does stay in the same position relative to the hole if I rotate the propeller. I am going to find a marine engineer who can replace engine mounts, which I hope that I can purchase from Lancing Marine, and then ensure that things are in alignment.


    Hi Nick, Apologies I have just noticed your reply! Hope you are all sorted now and back in action. Best Regards, Rod

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