The Perfect Engine and Shaft Alignment

[Lee Hadjiosif-H310]

Last summer I had realized that I had to do something about the shaft vibration but I wanted to do the perfect alignment, not just bring the coupling flanges to within acceptable tolerances. So I devised this new method and replayed it over and over in my head until the boat got hauled last October and got a chance to practice my concept while high and dry. This method requires that the cutless bearing be replaced at the same time. You will need: a)new cutless bearing and removal tool, b)video camera with long cable and a portable TV, c) A lot of time and patience. Here is the procedure-1-Disconnect and separate the output and shaft couplings. 2-Remove the prop and cutless bearing. (Use the proper tools-banging won't work).3-Back the packing nut off and remove the stuffing material.(It's better if you also remove the flex hose from the log tube so you can center the shaft through the tube as well).4-Place the video camera on a tripod between the rudder and the end of the shaft so that the camera is looking straight down the axis of the shaft as it passes through the strut. Connect the camera to the monitor inside the boat by the stuffing box where you will be working.5-Clean the contact areas of the couplings and use emery cloth if necessary to make perfectly smooth.6-Tighten the couplings together as tight as you can and use locktide if the nuts have a history of coming loose. (I replaced my bolts and nuts with new).7-Loosen the nuts on the engine mounts and adjust until the shaft passes through the center of the strut and without coming in contact with the strut walls. You can monitor this on the TV next to you with the camera you have set up outside. When you think you have it right, rotate the shaft by 90degrees and adjust again. Rotate and check again. This is the most critical part so spend as much time as you can here. Tighten the nuts on the mounts and grab the engine and shake it a hard as you can(simulate operation) and check alignment again. When you think you got it right, tighten the nuts on the engine mounts. Note that there is zero gap between the flanges and the shaft is perfectly centered through the log and strut.8-Install the cutless bearing and prop. Install the packing nut. You can loosen the flanges and check alignement after launch if you want to know if the hull shape has changed. Since I had no vibration, I didn't do that.I did this a few months ago but did not want to post this until I actually launched the boat and verified my theory. The vibration almost disappeared at all RPMs.Note: I was planning to replace the cutless bearing and install a dripless shaft seal anyway.

 

[Doug T.]

But...

That's all well and good for getting the shaft in perfect alignment while on the hard. The only defect is that the shape of a boat's hull frequently (always?) changes slightly after it's put back in the water. The water supports the hull differently than the stands do. The difference may be slight, but it can be enough to throw off your "perfect" alignment. You may have been lucky this time around, but the recommended procedure is to fine tune the shaft alignment AFTER the boat's in the water.I'm kinda surprised no one has invented a shaft balancing/alignment gizmo that could be attached to the rotating shaft while the engine is in the water and that would tell you how much & which way the shaft is misaligned. Something like the dynamic tire balancers at the auto shops....

 

[Gene]

Difference between wet and dry

Doug raises a good point about the boat flexing once floated. On the other hand, Lee clearly was successful with this method. The fibergalss around the engine and shaft area is awfully thick and reinforced. I would think that there would not be much flexing between the engine and the shaft outlet, otherwise alignment would fluctuate too much while under way. Certainly Lee's experience shows that his technique works, and while the "flex-in-the-water" caution makes sense, it looks like Lee's approach is a good one. Obviously, if, once in the water, an inspection shows that it's not aligned, an additional adjustment can always be made. I think this technique is a great new approach worth investigating and analyzing further.

 

[Mike DiMario]

Rotalign

I work for an industrial contractor. They own a rotalign which uses a beam to do shaft alignments. I havn't looked to see if it can physically be used in the space available on the shaft. It's primary use is to align motors and couplings with pumps and other rotating equipment. Since some of this equipment is very high speed, it has the capability of very close tolerances.Someone in your area may own one, if you're interested. Check out the site on the link!Mike D

 

[Don Alexander]

Shaft Sags

I had my strut off a couple of years back and tried the same method to get it back in the correct place again but I found that the shaft sagged between 1/8" and 1/4" under its own weight thus nullifying the technique.It has always seemed unsatisfactory to bolt a shaft up solid to the gearbox flange but have the engine on flexible mountings. What could be a perfect alignment when stationary must become totally wrong when the engine vibrates and the prop thrust comes onto the engine flex mountings.I fitted a vibration absorber between gearbox and shaft flanges in the hope of partially overcoming this.Manufacturers may have thought a solid coupling was okay in the days when engines were just bolted down to the bearers but things have moved on so why do they still do it?Regards,