Re: Prop Shaft Squeak
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ngtnewington Newington
Hi James,
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Since you plan to pull the shaft and check it at a machine shop you should also check that the prop is true. Many years ago (1991) I had a similar problem, it was on my first boat a 35’ gaff cutter. In Venezuela I installed a new engine, but the whole drive train was never checked. By the time I arrived in New Zealand I had only put on 200 hours as there was obviously a problem. Anchored off Russel in the Bay of Islands I pulled the prop and shaft, bunging the hole from inside and out. The machine shop right there checked the shaft, and it was bent. He checked the prop and it was true but completely the wrong prop for the type of boat. At very reasonable cost he supplied me with a second hand shaft and a second hand prop. I then went to town on the alignment and got it spot on. From that moment on engaging gear was a silky smooth transition and gradually powering up and loading the engine was a joy. The point being that the whole power train from engine to prop is critical. I suggest in addition to checking the shaft, you have the prop checked for balance. As James on Sueno says, the cutlass bearing might need “bedding in”. It should not be tight. It should be only bearing on the bottom due to the weight of the shaft with a very slight gap above and around. So there is a tiny bit of wiggle and you should be able to turn it by hand easily. The alignment: I see the shaft alternator and coupling arrangement from your photos. I suggest that initially you slide on the temporary nylon bearing down the shaft so that it sits in the stern tube and the shaft is then supported for and aft with minimal wiggle. Then gently slide the shaft forward so that it kisses the coupling. If it slides perfectly into the coupling slot without pushing it up or down or to one side then the alignment is already pretty good. I would then using feeler gauges check the alignment on the coupling to the transmission whilst rotating it. I am not sure that you actually need to remove the alternator pulley. If you want to, then the shaft should reach with the prop removed. I have said that the alignment is critical. However given the fact that there is no bearing forward, only a piece of exhaust hose and a lip seal that can move about quite freely, and given that the cutlass bearing must be at least three or four feet aft of the engine and the cutlass bearing is maybe five inches long. Also given the fact that the engine is mounted flexibly. I would say that the alignment needs to be such that the shaft slides without force into its coupling would be good enough. In my story above the engine was solidly mounted on hardwood blocks and there was a grease gland bearing at the forward end of the shaft. Alignment was very very critical. In your case it will not be so critical. I still think however that the technique to centre the shaft with a temporary nylon bearing is a great way to get the proper datum from which to work. Regarding the squeak being between 1500-1800 rpm. It would not surprise me if either the prop or the shaft, or indeed alignment is the problem, or even all three. Nick Amelia AML 54-019 Kilada Greece
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