Shaft noise

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  • #3560
    Alun Pari HuwsAlun Pari Huws
    Participant

    My Mac 26 Mark was built in 1966 and bought by father in 1980. I have owned her since he died in 2003. I stripped her 2013/14 and refitted at some cost but did not interfere with a number of original parts a. on the grounds that costs were running away and b. because of the old adage ‘if it ain’t broke, don’t fix it’. I did the work myself apart from the engine aspects including a complete rewire. She looked like new. The original Volvo Penta 7HP (still running) was replaced with a Beta 20 fitted professionally with a new shaft in the original bronze tube.  Whilst happy with the engine’s performance on the water (bearing in mind tides in the Menai Strait) there has been some disappointment with clogging of the tubes in the heat exchanger from rust deposits requiring 2 x flushing exercises at some cost. I’ve since discovered that the engine was manufactured a full 12 months before it was fitted so maybe standing idle with no anti freeze contributed to this. Also, the cutlass bearing had to be replaced after only 3 years which was an expensive job as the engineers insisted on removing the engine into the cabin to withdraw the shaft – the rudder cannot be easily withdrawn. When the Volvo was in I’ve no memory of needing to replace the bearing!   In late 2020 I took the boat out of the water for some months as I had a deck paint issue, general maintenance and needed to replace several valves, something I should probably have done on the major refit in the first place.  The engine was serviced again by the original engine fitters but they pointed out play in the shaft. Indeed there was some 3mm of play. Still unhappy with previous bills, I engaged another well thought of marine engineer I knew of. He replaced the cutlass bearing at a very reasonable cost. However, only months later, I am experiencing a grinding noise, once again, when I first engage the boat in gear. I’ve only done about 30 hours steaming since the bearing was replaced. The nut on the stern gland does have to be adjusted regularly to regulate the amount of ‘drips’ coming through to cool it – too loose and I can come back to the boat after two weeks to a lot of pumping out from the bilge and too tight it risks overheating the shaft and bearing. I sometimes have to ‘nip’ the nut with a slight tightening when the engine has run for a few hours. Anyone else with similar experience? Ordinarily, I would not be intending to take the boat out of the water until 2023 for a look see and anti fouling. Every two years is normally quite often enough.

    #3563
    Chris NixonChris Nixon
    Keymaster

    Hi

    It sounds like you need to take the heat exchanger apart and clean all the tubes and flush the entire engine out.

    As for the shaft cutlass bearing, this should last a good few years. So it could be that the engine is out of alignment which would also  make your seal leak.

    Have you repacked the seal lately and do you grease it after every trip?

    Also as a side note, it’s good practice to lay the boat up out of water for a few weeks/months each year to allow the hull to dry and any below water maintenance to be completed.

    Chris.

    #3565
    Earnon O'CleirighEarnon O’Cleirigh
    Participant

    Alun,

     

    On old boats there is often a white metal bearing integrated with the stuffing box supporting the shaft at the forward end of the stern tube. If you have 3mm of play in the inboard part of the shaft, this bearing is probably worn. This is also more likely to be the source of a grinding (metal on metal) noise – a worn cutlass bearing gives more of a rumble.  The bearing surface can be replaced, but it is a job for a machine shop – especially if the shaft has also suffered.  If the bearing is the problem, ir might be worth looking at replacing the whole stuffing box and bearing assembly with a more modern one.

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