Bent Shaft

backman

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Going through my running gear this winter - engine alignment, replacing worn cutlass bearing, checking dripless, etc - everything came out.

This was prompted by the need to re-align the engine as well as deal with a visibly worn and misaligned aft cutlasss bearing. A quick check of engine alignment this summer showed it off by 60/1000".

The shaft had groove and wear on it at the aft cutlass bearing so it got sent out to H&H for repair along w. prop and coupling so everything gets refaced together.

To my surprise they found the 146 X 2.25" shaft 9/1000 out of true at the aft end, 8/1000 at the coupling and 6/1000 in the middle. Not a big deal for them to straighten while welding up the grooves in the shaft.

Questions:

Is this "normal" and expected for a 5 year old shaft w/ only 1000 hours on it?

What is the alignment tolerance for a 2.25" shaft in a 36' DE w/ 670 HP?
 

backman

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It had a rumble at dead idle and a couple intermediate trolling RPM's had some rumble also, it evened out at cruise speed, but it was definitely worse by end of year than at the beginning.
 

Blitzen

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Don you stirring the pot?:D
 

Kaiser

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wonder if that is a single deflection, multi deflections, twist or combo there of. also wonder how straight the shaft originally was? .009 seams like alot. Half of that is more acceptable
 

backman

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Multiple deflections - .009 at the prop end .006 at the cutlass end and also something smaller in the middle. 146 X 2.25" shaft
 

Kaiser

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so i guess if you have three separate deflections with the shaft being back to dead center in between each deflection. one from the prop cantilever, one from coupling misalignment and one from torsional loading. What was H&H thoughts on that. Those guys at RI diesel are pretty clever too.
 

harmuthmarine203

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If your going thru all that you better change your engine isolators (mounts) i have seen lots of boats being more the 90 thous out and never had a vibration, but a failing engine mount can make alot of wierd harmonics and vibrations and even tricking you into thinking you have a engine problem. Also a failing engine mounts will get progressively worse as a season gose on which will if it gets bad enough will bend your shaft and wear out your cuttlass prematurely. Most engine manufactures will tell you to inspect your engine isolators at 500hrs and replace at 1000 hrs. If you think about it you can change a the alignment of the engine by just leaning on the engine. When ur doing a alignment the biggest thing is not to do the final check till the boat has sat in the water for a fewdays every boat moves no matter how well the are built. the other big thing is while moveing the motor around is make sure to dissengauge the pilot bore often to check that your not side or vertically loading the shaft.
 

backman

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The guys at H&H said the same thing - 3 deflections, all countering the mislaigned engine. I will have the isolators looked at during the process.

It should be noted one engine mount was loose a year ago when I first pulled the boat and the cutlass bearing showed significant compression in about 1/3 of its diameter. I had other engine issues going on and put off the running gear till this winter.

Now its time to get it all right at once....
 
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Generally accepted transmission output flange to prop shaft coupler flange alignment is a maximum of .002" per inch of shaft diameter. 2.25" X .002" is .0045". Set your aft mounts so that the shaft is fairly centered in the wet tube or shaft log and slides easily through the cutlass up onto the gear output flange pilot and then do your flange face to face aligning using the front mounts/isolators.
 

southshore30

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Last edited:

Brooksie

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I am going to try to attach below an article I wrote for one of the DIY boat magazines some years ago which may be of help to you in getting things lined up when you reassemble. I'm not sure the pics are all there or in order, but you'll get the idea.

A COMPLETE SHAFT ALIGNMENT​

So you think your shaft is in alignment because you have fussed with a feeler gauge or strips of paper carefully turning your transmission and shaft flanges and laboriously moving your engine from side to side and up to down while crawling about in bilge water and oil for hours? Finally you have gotten everything within specifications. Maybe you have even rechecked after the vessel was launched to insure nothing had changed. Very good. But your shaft could still be way out of alignment...
The above procedure is correct and well known to all. However, it is only half of a shaft alignment job and the second half at that.
Before aligning the shaft flange with the transmission flange as detailed above, the shaft flange must be where it belongs in the vessel in relation to the cutlass, strut, and or center support bearings; otherwise excessive wear and binding will occur. Bearings, shaft, & efficiency all suffer if the shaft does not proceed straight and parallel through all bearings to the transmission. Only then is the relationship between those two flanges you have been fussing over relevant.
A good method to achieve the first part of the alignment procedure is as follows. As an example, I am using a vessel with both a cutlass bearing and a center support bearing. A cutlass & strut or a cutlass, strut, & center support combination would be addressed similarly.
What is needed for equipment can easily be made in a home workshop. First: a disc of plywood matching the transmission flange diameter and bolt holes. This needs to have a 1/32” hole bored exactly in its center. Second: several 1” slices of wood dowel the same diameter as your shaft with 1/32” holes exactly in their centers. Third: a piece of single strand wire (like wire trolling line, safety wire, or light bailing wire) a few feet longer than your shaft. Finally: some misc. wood blocks (although a jack-stand was used in the photos) and a 10-15 lb. weight.
 
 
To get started you must remove the shaft. You needed to replace a bearing, packing gland hose, clamps, or packing anyway didn’t you? It is also a good time to check your shaft for straightness or have it checked and straightened.
Now, after placing one end of the wire through the plywood disc and knotting it so it can’t pull through, attach the disc to the transmission flange. Pull the other end of the wire aft through each of the bearings placing a dowel on the wire fore and aft of each bearing point. Drape the wire over blocks or a jack-stand and weight the exterior end so that it is taut. Using the first dowel as a gauge center the wire exactly in the aft end of the cutlass bearing by raising the wire up, down, left, or right on the blocks/stand to do so. The dowel should not be holding the wire in the center; it is a gauge, to check if it is centered. Go to the forward side of the cutlass bearing and see if it is also centered on the wire using another dowel as a gauge. Now work forward to the other bearings and see if they are all centered on the wire and that the wire is perfectly square with the disc on the transmission.
If all is as it should be, you may proceed to the usual feeler gauge flange alignment procedure but if not, you must start moving things around to get the wire centered in EACH END of EACH cutlass/strut bearing and each center support bearing while being at 90 degrees to the transmission flange. This can involve anything from moving and/or tipping the engine or one of the center support bearings to changing the relationship between a cutlass and a strut bearing by bending one and/or remounting the other.
If your shaft would not turn by hand before, you may find that it was bending on its passage through the various bearings and then the engine was misaligned to make all seem right in the feeler gauge test. Over several years and owners, these errors can become quite large and start to show up with cutlass bearings worn in one quadrant on one end and the opposite quadrant on the other end, not to mention shaft whipping, wear, and transmission bearing problems. Additionally many horsepower are needlessly consumed in friction. I think we have all seen stern tubes worn through by shafts rubbing and vibrating on them where the owner insisted his alignment was checked and set with the feeler gauge test every year. Well, somewhere along the line, the shaft was dropped on the bottom of the stern tube and the engine was aligned to it as it lay on the bottom of the tube. All nice to “spec” as far as the shaft and transmission flanges being concentric and parallel with the feeler gauge test.
You will usually find that the engine needs to be raised quite a bit because over a period of years the engine may have been aligned to a drooping shaft.
After the above procedure even fairly large shafts should turn easily by hand and future minor “feeler gauge” alignments can be carried out with confidence as long as in doing them, the transmission flange is not moved from the position you have established with the wire procedure.
 
Photos & Drawings:
Photo: wooden centering disc.
Drawing: a strut with the shaft “cocked”
Drawing: setup with the wire in place of the shaft.
Photo: wire, looped over stand, weighted, and centered in aft end of a cutlass bearing.
Photo: checking centering with shaft sized dowel on the wire.
Photo: centering disc and wire attached to transmission.
Photo: a center bearing with wire and centering dowel in it.
Photo: a stuffing box with wire & centering dowel in it.
Photo: a bilge with wire through a center bearing and a stuffing box.
Photo: an example of an un-square wire at the transmission flange.



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Toolate

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Great work Brooksie- I asked about this a couple weeks ago and had no responses- here it is in color.

Where did you get this bearing? Looking for alternative to my CI babbit.

Talking with Baldor now and they have a SS model like this but waiting to hear if its up to the task.

THx

image.jpg
 

Brooksie

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Great work Brooksie- I asked about this a couple weeks ago and had no responses- here it is in color.

Where did you get this bearing? Looking for alternative to my CI babbit.

Talking with Baldor now and they have a SS model like this but waiting to hear if its up to the task.

THx

Sorry I missed your question b/4. I bought it online, it is SS, in a glass filled nylon housing, it was cheap, and has been in place 7 yrs. I can't remember where I got it. Maybe Grainger or McMaster Carr. B/4 this I had the same thing only not SS. The babbit one always rattled and it wore the shaft.
 
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