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Old 05-11-2014, 11:16 AM   #1
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Shaft Alignment

Ok, so I know I've been asking a lot of things the last couple of days but I really appreciate the info.

So I have a single shaft with one cutlass bearing at the prop end and a standard stuffing box that I am using PTFE packing in up where the stern tube comes through the hull.

The shaft is probably at least 15' long. Once it comes into the boat there is probably 6' at least coming to the flange that mounts to the tranny tail shaft. The shaft is 1.5".

When I unbolted the shaft flange it dropped about 2" or so because of the shaft drooping down. I have searched the forum to see how to do the alignment. Since I have not done this before is it better to hire a mechanic to do this or is it something I could do? I do all my own mechanical but maybe need to see this done? I don't know what the trick would be to figure where straight would be on something like this. I get moving the engine around to align it. I have done that several times on another boat but it was a stern drive. I just need to figure out how to center this shaft so I can adjust the alignment.

Thanks,
Jeff
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Old 05-11-2014, 11:55 AM   #2
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Where the shaft goes through the stern tube (where it goes out the hull) there is the packing gland and a short length of hose joining them. Usually there is a pretty good amount of clearance between the shaft and tube, and as you noted when disconnected, it drops. It drops til it contacts the inside of the tube. The shaft also flexs due to its weight.

The trick is to lift it up so it now contacts the inside top of the tube. If in this position the tranny flange is now about the same distance as it was when resting (up now instead of down, i.e., centered) then things are pretty close and next step is to do the feeler gauge thing. The goal is to have shaft roughly centered in the tube, and the hose piece not deflected up or down. Also shove shaft left and right and see that it goes about the same distance from tranny flange.

This takes a little touchy feely experience, as you kinda have to estimate the weight of the shaft and thus how much force to lift it.

Also make sure to clean clean clean the mating flanges. Can't count how many times a film of rust kicked shaft out causing vibes near packing.
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Old 05-11-2014, 12:00 PM   #3
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There are many instructions on the net for aligning your shaft and some deal with the "droop factor" Basicly, you want to find the weight of your unsupported shaft, offset that with a spring scale, making sure the shaft is centered in the tube and going straight through the cutlass bearing, then bring the engine to meet this, finally making the normal fine adjustment with a feeler gauge.
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Old 05-11-2014, 12:50 PM   #4
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It helps on final adjustment if the shaft flange has a pilot that fits in the gear flange.
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Old 05-21-2014, 03:29 PM   #5
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So I am still fighting this. I have been able to get the alignment within a few thousandths but still vibrating. I am guessing it is because I don't know if the shaft is in the middle of the stern tube.

The boat is in the water. I know this sounds stupid but can you take the stuffing box off with the boat in the water. I understand you will get all the water from the cutlass bearing, just not sure how much that is. I do have 3 separate bilge pumps theoretically able to take out 4600 GPH I would not do this if I am told a bunch of water comes in.

I have been told you can replace packing while in the water, just didn't know how far that extends!

I need to get the shaft supported in the stern tube to figure out the height to align to. Can't use any of the measurements until I know where I am starting at.

Thanks,
Jeff
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Old 05-21-2014, 03:49 PM   #6
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sure...pop it off...just have plenty of rags, a hammer and wedges at hand.

Also make sure the travel lift guy is still around not not at lunch or gone for the day...

Actually the better solution is try to plug it all from the outside but if not it's not a huge deal as long as you are prepared.

In many places thru hulls are drilled and installed in the water...not the best in the world but it's worked in many, many cares....
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Old 05-21-2014, 03:53 PM   #7
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A cutless bearing will pass much more water than a packing gland without packing. You can try it, but be ready to slide hose right back on if flow rate is more than you can safely handle.
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Old 05-21-2014, 05:34 PM   #8
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Quote:
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I know this sounds stupid but can you take the stuffing box off with the boat in the water. I understand you will get all the water from the cutlass bearing, just not sure how much that is.
Go to Lowe's or Home Depot and get one of the wax seals which go around your commode pipe (at home) when you seat it. That will seal the shaft entry enough if you mold it to the entrance at the cutlass bearing, so that the water trickling in is manageable. There will still be some, but not enough to cause panic.
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Old 05-30-2014, 01:01 AM   #9
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I have just replaced my cutlass bearing and am very interested in this thread. I had a recommendation from the surveyor to change the bearing but had too many projects and not enough time last year. Is it an acceptable practice to simply use a dial timing gauge to check the rotation of the shaft at the coupler? I strapped the gauge onto a board and turned the shaft by hand, there was NO deviation on the dial gauge. I am having to learn so many new things...
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Old 05-30-2014, 08:20 AM   #10
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No, a dial indicator on the shaft is not going to tell you much about the alignment.
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Old 05-30-2014, 08:37 AM   #11
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AKDoug,
I don't think the dial indicator is going to be the tool for the alignment. You need to separate the shaft coupler from the tail shaft and let I sit on the ring that is typically on the coupler. It allows you to just barely separate the two pieces without the shaft dropping off. Then use a feeler gauge to measure the alignment. This allows the shaft to freely move as you check it. Any mis-alignment is noted as the coupler is closer or further away from the tail shaft.

I am new to this and there are several you tube videos on how to do this.

Shaft alignment can be very time consuming as a small adjustment on the motor to move it one way might throw off a different angle. I would do it different next time in NOT moving a dang thing until I was positive I needed to. The alignment should be pretty close to what it was before you changed the cutlass.

Jeff
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Old 05-30-2014, 10:11 AM   #12
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dont touch it.

Agree! if the alignment was fine before the cutlass was installed I would just bolt things up. I installed new shafts, couplers and cutlass bearings the other year. Everything was fine just bolting things back up. Pull a strut or engine and thats a whole different story.
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Old 05-30-2014, 02:17 PM   #13
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AKDoug,
I don't think the dial indicator is going to be the tool for the alignment. You need to separate the shaft coupler from the tail shaft and let I sit on the ring that is typically on the coupler. It allows you to just barely separate the two pieces without the shaft dropping off. Then use a feeler gauge to measure the alignment.
That's right. . .dial indicator will show you if you have a warped/bent shaft, but the actual alignment at the trans. coupling must be done with a feeler gauge as described.

Get someone who has done it before to help you. . . it can be a pain in the rear the first time you do it. Too many different adjustment directions to go and adjusting one way will invariably throw the other way off.
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Old 05-30-2014, 04:29 PM   #14
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My interest comes largely from the fact that the cutlass bearing was worn (or environmentally degraded over 14 years on the hard) enough at 46 hours to be recommended for replacement. I put 600 hours on it before replacement and I now have a point of reference that means something to me to measure the wear from. There was only slight vibration during operation, which leads me to believe it was correctly aligned or very nearly so. Of course I destroyed the old bearing removing it so there was nothing to examine. I saw an article which displays two dial gauges mounted opposite to each other, one on each side of the coupler. The caption stated that this was a normal practice for aligning during construction. I am always looking for the easy way out :-)
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Old 05-30-2014, 05:46 PM   #15
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Try and get some one who can do laser alignment.

Running Gear Alignment - Professional BoatBuilder Magazine

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Old 05-30-2014, 08:16 PM   #16
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That you tube video was pretty vague about alignment. It did touch on in important issue about lowering the front or raising the rear will a lot of times depend on the shafts location in the shaft log. The first thing you want to do is separate the coupling and run a fine cut file over both coupling surfaces. The metal will often be slightly raised around the bolt holes. What type of motor mounts do you have? If the adjustable thread type make sure you can actually turn the adjusting bolt. You may have to take them off one at a time and clean them up. You want the clearance less than .003.
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Old 05-30-2014, 08:37 PM   #17
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The video gives me a good idea where to check first, and I suspect that I am not going to have to make any adjustments. I haven't really looked at my motor mounts, the 50 HP Yanmar and it's 1 1/4" shaft (5 1/2' long) probably don't put a lot of stress on the mounts. The hull is pretty short, I figure probably not more than 26' at the waterline, and that compactness should help everything to be pretty stable. IF I find things out of alignment I will probably give the local Yanmar dealer a shot at adjusting it the first time, while I observe. On the job training, so to speak :-) Thanks all...
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