Stern tube for prop shaft

[William Niessen]

It seems I have found another common problem, my 37 Legend's prop shaft is rapping at a particular RPM,(1800) I went through the archives and can find numerous comments but I still have a couple questions that someone may be abe to help with. The cutless bearing on the strut is nice and tight - not .010' play, but the shaft can be moved easily where it enters the stern tube. My question is "what kind of bearing is in the stern tube?" Is there another cutless type bearing in there or does the shaft just go through the stern tube and through the packing bearing.When the shaft is rapping you can hear grinding in the stern tube if you put a screw driver against it and listen with yor ear against the screwdriver. Increase or decrease the engine rpms and it goes away. I expect it to get worse at the wrong time - so want it fixed, could not find an exploded view of the shaft tube and packing gland. Can anyone explain this assembly? (I plan to take it apart soon.)Thanks

 

[Steve O.]

noisy shaft

Usually you can trace this kind of noise to one or more of these three problems: 1) bent shaft or prop 2) worn cutless bearing 3) shaft out of alignment. (a loose prop will rattle, but I'm assuming you've eliminated the obvious) Diesels are inherently prone to vibration so you will never eliminate it completely. There is no bearing in the stern tube, only packing to keep out seawater.

 

[Charlie Griffith]

It's an annoying problem and could be expensive to

I experienced the same thing with an 11 year old Tartan 34. First, I aligned the engine. This helped but did not totally solve the problem. It got worse over time. A year later I had the propeller shaft pulled and found it was bent in three places. How this happened is still a mystery. The problem did not exist when I purchased the boat and I had never hit anything that would cause a shaft to kink. A new shaft eliminated the rapping but the grinding continued and got worse over time. Finally a transmission overhaul eliminated the grinding. I am told that the "cones" inside the Kanzaki transmissions that are furnished with Yanmar diesels simply wear out over time and have to be replaced.To my knowledge, there is no bearing inside the stern tube supporting the shaft. Good luck!

 

[Paul McGhee]

Great explanation in Calder

If you have a stern tube, there's a rubberized sleeve inside of the tube. That's a cutlass bearing.I have a copy of Nigel Calder's "Boatowner's mechanical and electrical manual." It has clear diagrams of most configurations, suggestions for tools to remove and replace, and some diagnostic suggestions.If you can't find it at your bookstore, Amazon probably has in in stock.Paul McGheesv Escape Artisth336

 

[Brian]

No bearing..

I THINK what you are talking about is where the shaft is leaves the boat and the shaft is resting on the bottom of the hole? If this is the case, then the problem is alignment and can be fixed in a two step process. The mechanic can first align the shaft while out of the water to make sure it is not touching the hole, and then realign once in the water...At least that is what Hunter is telling me after looking at my 380 on "the hard" the other day.Brian

 

[J. Tesoriero]

Some Hunters has bronze stern tubes......

....and they corrode and can fracture. I found this out the hard way. Apparently some early Hunters (mine is a 1980 30") have a bronze stern tube (shaft log) rather than a glass tube. You can tell by looking at the stern tube from inside the boat. If there are 3-4 bolt heads sticking through your hull then you have one of these metal fittings. You can also see a metal flange around the stern tube from the outside. There are no bearings inside but the shaft can grind against the fitting if either the engine or the strut are misaligned.The prop strut must be aligned so that the shaft is centered in the stern tube and then the engine can be aligned to the shaft.