Shaft Coupling

[John Rutherford]

So I have this shaft coupling thing-a-ma-bob on my HC38. It is a source of much fuss for us since it is worn and allows the shaft to rattle quite loudly and with some noticeble vibration. I just had the engine professionally aligned so I know this is not the issue. When you sharply yank on the forward shaft section you can see, hear and feel the shaft movement within this couplining's solid bearing. At higher RPM under load its very noticeble. So what I hope to learn here is can I replace this, where do I get a replacement (of same type), could it be safely removed....etc. Oh and is this the proper name for this thingy? Thanks
hcoa@dessein.com

[Ken W.]

From the photo it lools like a standard pillow block. I assume that there is a fairly long distance from the stuffing box to the engine, so they installed an intermediate bearing to support the shaft. If all this is correct, you should be able to get a replacement from any industrial bearing supplier. Ken kc8pql@arrl.net

[Stephen Carstensen]

John, I agree with Ken that this looks like an industry standard pillow block bearing. I went through a similar bearing search while replacing the bearing on my rudder shaft. After a lot of research I found that fully stainless steel units were available at a price them makes them an attractive alternative to steel. I'm attaching a reference to the company I used, that shows a table of available sizes. Best, Steve
warmrain@rockisland.com

[Administrator]

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[Mark Raine]

John,
We had a pillow bearing our 38T and its mounting base platform was so poorly attached that I was able to remove it by hand. At the time we bought the boat (1998) we replaced the shaft after noting a lot of crevis corrosion. The pillow bearing was not in place then and I dont know how long it had been "out". I elected not to replace it. We have thus far put about 700hrs on the engine since not having the pillow block inplace.
All appears well. I am checking run out with a gauge and the shaft is running true. Thereis no "play" in the cutless bearing.
Some time back the topic of pillow bearing came up and as a result of that dicussion I did some investigating of my own application ( or rather the lack of it).
Here's what I learned. The pillow bearing provides support of a long shaft. The definition of a long shaft has to figure in the diameter of the shaft and the loads involved. Alligment is important, a poorly alligned shaft will not be "made better" by simply having a pillow bearing.
As you know the length of the shaft will vary with the location of the engine. Typically the issue is the pillow bearing for an engine located under the sink. The shaft length for engine under the steps is so short as to make a pillow bearing of little value.
Discussions with professional mechanics who were willing to apply their engineering/mechanical knowledge experience to the problem suggested that for the 38T 1 1/2" SS shaft on the Isuzu 240 60hp, that the pillow bearing was not necessary and probably not helpful given its proximal location to the coupling.
It may be useful to run through these numbers yourself with your local mechanics or prop/shaft experts. I'll grant that the easiest thing to do is to just put it back. Short conversation and it doesnt require any thought. If however, it isnt necessary....
Opinion from this group runs against what I have said and done, but I believe the specifics like HC Model and shaft length are in fact different as well. So.... food for thought
Mark
svedelweiss@yahoo.com

[Lewis Whitesell]

John,
If you just had your engine and shaft professionally realigned, how is it that your professional missed so obvious a defect in the process? I suppose it just kind of came unglued since? Seems a solid bearing wouldn't do so that quickly.
The photo is a bit fuzzy but it appears that where the shaft enters the carrier bearing, there is some kind of stuff like a silver colored goo. Is that grease? Have you checked it for SS shavings? Just concerned that your shaft may be getting honed down by a faulty bearing. That would make replacement much more difficult. Also, you said that it is a solid bearing, the one on my shaft is a roller bearing with a grease fitting, very smooth.

[John Rutherford]

Mark thanks for the other view, I am actually considering removing the pillow block all together (also known as a plumber block for what ever reason). I would love to get rid of that greasy relic in my bilge. Although replacement is inexpensive and not time consuming. Our previous boat had a longer shaft of same diameter, more HP/Torque and no shaft support. No side effects at all. Lewis. Yes that is grease you see. The pillow block is not typical of what I have been seeing. It has no ball or roller bearings. It is purly a greased pillow block with what appears to be a bronze inner surface. As for the mechanic that did the alignment. The pillow block was a long point of discussion. He recommended replacing or rebuilding it. It is worn to the point where the shaft has too much play inside. It' all original equipment. Thus teh noise. The SS shaft is in really good shape with no wear since the previous owner greased it yearly. However I may need to take it to a shop to check it for sure. Thanks for the input. hcoa@dessein.com

[Ken W.]

John,
Dave Gerr NA has a graph in his book "The Nature of Boats" showing maximum bearing spacing for shaft diameters from 3/4" to 4". According to this graph, maximum bearing spaceing for a 1 1/2" shaft is 66". He also says that bearings shouldn't be closer than 20 times the shaft diameter. Hope this helps. Ken kc8pql@arrl.net

[Mark Raine]

And the length of a HC 38T shaft is ????? Anyone know? svedelweiss@yahoo.com

[Stephen Carstensen]

Ah a plain bearing pillow block bearing... I would replace it with a roller bearing type IMHO. Hopefully you will not have any shaft wear in that location. I can't recommend removal over replacement. But I would recommend caution and a conservative attitude... I'm thinking that having the mid-line support may take some of the load off the shaft log and cutlass bearing... - Steve warmrain@rockisland.com

[Lewis Whitesell]

I don't know if it would pertain on this scale but I was recently talking with a navy guy and he said that, on large naval vessels at rest, the shafts have to be turned periodically a specific number of degrees in order to prevent the shaft from "memorizing" the sag. Perhaps even at this scale, a shaft without such a bearing at rest for some period could have a small bow imprinted which could lead to vibration and the premature wearing of parts. Maybe so, maybe no. The shaft is somewhere(very roughly) around 8' (96") as scaled from my blueprints. Probably a little less. Lewis

[John Rutherford]

I guess anything is possible. But on this scale garvity would have to be significantly stronger. On the Navy vessels, if memory serves, the shafts are HUGE, ENORMOUS, bigger around than me even. The sheer weight of the all that metal is enough to counter the load bearing strength of steel. Based on everyones comments I think that I am going to replace the pillow bearing. It is there for a reason. I can get a full SS unit with a roller bearing insert for around $100 or less. SUPRISE a part for a boat that does not cost a gagillion dollars. Whod'a thunk-it. Further I now have reason to believe that the long shaft section might not be true. The engine is so perfectly alligned (within .005 inch) any vibration has be coming from the shaft. So I will have it checked when we come out of the water next year. As if I don't already have other things to do. hcoa@dessein.com

[Stephen Carstensen]

"The engine is so perfectly alligned (within .005 inch)..." I think that is the goal, at least it was for our yard... - Steve warmrain@rockisland.com

[Bob Pleischl]

I may be missing something but my HC33T hull #76 did not nor does not incorporate a pillow box. The shaft length is approx 3'. Steve, I believe you also have a 33 and have a pillow box. I have not experienced any problems with the shaft or the cutlass bearing. I have somewhere in the neighborhood of 4000 hours on my Yanmar 30. rpleischl@sailtime.net

[Stephen Carstensen]

Bob, Your experience is the same as mine. The shaft on the 33 is so damn short that no other support is needed. However the result is that the engine is mounted at the very limits (and sometimes beyond) of the specifications. Which state:
The installation angle shall not be greater than 15 degrees (the 33's Yanmar 3QM30FG is at 14). And running shall not exceed 20 degrees. Well you can only imagine what happens in a real sea-way. We are already within a degree of the installation limit. And so being, it is not difficult to exceed the running limitation. When this happens you get a little chirp from the oil pressure sender unless you keep the oil right at the very top. Normally too much oil can cause the danger of blowing a seal. However we run with the oil level at the top of the "flat spot on the dipstick" and find that to be ideal. We had a certified Yanmar mechanic down with analog instruments (which were used in place of the standard senders) and tested the pressure to be sure we were still within spec. The result were that filled to the top of the fill mark on the dipstick we were too low in pressure, and filled to the top of the "flat spot" we were AT spec. It takes about 2 gallons to the tope of the flat spot. Otherwise what happens is that when you start climbing waves while motor sailing and beating, you keep getting chirps from the low oil pressure warning horn as the engine sucks air inthe oil pan. But now pillow block, but I did find a great supplier for those that need them while I was searching for a fully SS bearing for my rudder shaft. Best, Steve warmrain@rockisland.com