Re: Prop Shaft Squeak

ngtnewington Newington
 

Hi James,

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


On 25 Nov 2019, at 00:50, James Lochhead <j_lochhead@...> wrote:


-- Thanks Nick.  Your description is perfect.  I will have another go at the alignment.  Due to location and with no assistance around at the time I did it myself with only advice from other cruisers.

It is out of the water currently so I will try your proposal of the temporary bearing while out first when I get back to the boat and then check again once I get back in the water.  Will also get the prop shaft checked.

I have one other question if you could help.  Due to the prop shaft generator the belt pulley sits between the vetus coupling and the transmission.  I have attached some photos from another post that shows the arrangement.  from memory the 4 bolts shown on the photo "vetus coupler" bolt through the coupling and the pulley holding it all in place.
When measuring the the alignment access to the back of the transmission is limited due to the generator pulley.  I am not sure if there is enough length in the shaft to pull it forward without the pulley in place.  Do you have any thoughts on this?

Also it is only at certain revs that the squeak was occurring.  Very low revs and then between 1500-1800.

James
Maramu #147 (1984) <Prop Shaft Alternator.jpg><Coupling.JPG><Vetus coupler.jpg>

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