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Old 12-21-2018, 10:21 AM   #1
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Alignment check

I had a yard check my shaft coupling alignment recently. The yard reported that both engines were out by .008. The front of both engines need to lower. Problem is that the mount nut has no further adjustment. The engine needs to be jacked up and a thinner nut installed.
I had it checked due to a minor vib at higher RPMs. It turns out the props are out a little too.
Looking for thoughts on the alignment. The alignment was done in the water.
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Old 12-21-2018, 10:32 AM   #2
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Is 8-thou out of spec? We had ours done a few years ago, so I don't remember what our yard said was beyond acceptable spec of the best alignment. Ours was way off and we had to get larger holes cut in the mounting brackets to get it to go far enough over. Yours seems like a lot of money for 8/1000s... but if it is out of spec... by a lot... you should do it. If it is just 1 or 2 thou, it could probably wait until next trip when you have more to do. Are you going to have the props pulled a trued? Have you already fixed that and done a test run?
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Old 12-21-2018, 10:34 AM   #3
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Not a good idea to do an alignment on blocks. All hulls flex a little. 0.008" is not horrible.

Also, depend on how your shaft is run and how much wiggle room you have there, you may be able to dial it in by raising the back.

Make sure to clean clean clean the coupling mating faces. Amazing how a little crud there can kick out the shafts and cause vibes.
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Old 12-21-2018, 11:26 AM   #4
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It's good that the alignment has the engine close to the bottom of the isolator (mount).

You can remove the nuts and use shims if necessary to drop the front of the engine.
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Old 12-21-2018, 11:30 AM   #5
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When we rebuilt the engine I replaced the engine mounts. After a couple weeks while trying to do the final alignment, we had the exact same problem. The mechanic came back from his truck with a 3’ 2x3” piece of maple. We were able to raise the front of the engine off the mounts to put on thinner nuts. It’s amzing how much you can lift with a lever.
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Old 12-21-2018, 11:49 AM   #6
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It's good that the alignment has the engine close to the bottom of the isolator (mount).

.
Not necessarily.....My summer marina guys insist that near the upper end of the stud is better.

They are experienced in that, I am not.
I'm sure there are arguments either way.
Chevy or Ford I suppose (or should I say Toyota or Honda).
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Old 12-21-2018, 12:04 PM   #7
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Like always...different thoughts...

Actually, most people, including yards, really don't do the total engineering necessary so picking an average isolator will give average results. Thats assuming the performance specs are optimized for the engine to be near the middle of the adjustment range...up or down isn't necessarily better.

My choice is lower because as the mount detriorates, better lower and less movement than higher and more.
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Old 12-21-2018, 12:44 PM   #8
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The specs on my Vetus mounts suggest that it is preferable to have them adjusted at the lower end of the range. Different designs may vary so check with manufacturer.

In regard to being 8 thou out, I wouldn’t get too excited about that, especially measured on the hard. It may be less than that when back in the water.
I’d tune the props first then check for vibration before adjusting the alignment in the water if necessary.
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Old 12-21-2018, 01:22 PM   #9
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Alignment check done in the water is the proper way to do it as Ski points out.
What is the coupling diameter?
Typically a guideline is 0.001" out per inch of coupling diameter is OK. Of course closer is better and can usually be done.

Is there ANY movement in the lower nuts at all? 0.008 at the coupling may only need 0.001 or 0.002 drop at the engine front to at least get much closer.
The distance between the front and rear mounts will have an effect on how much the front really has to drop.
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Old 12-21-2018, 03:52 PM   #10
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Current plan is to tune props and see how she runs. Probably will wait until June to attack alignment.
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Old 12-21-2018, 03:54 PM   #11
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Quote:
Originally Posted by Ski in NC View Post
Not a good idea to do an alignment on blocks. All hulls flex a little. 0.008" is not horrible.

Also, depend on how your shaft is run and how much wiggle room you have there, you may be able to dial it in by raising the back.

Make sure to clean clean clean the coupling mating faces. Amazing how a little crud there can kick out the shafts and cause vibes.
Alignment check was done in water. Yards said raising aft end of engine won't work.
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Old 12-21-2018, 03:54 PM   #12
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I just had my props scanned and rebuilt. Won’t be able to tell how much difference that will make until we launch in the spring but it has to help since one blade on each was out quite a bit.
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Old 12-21-2018, 03:57 PM   #13
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Originally Posted by C lectric View Post
Alignment check done in the water is the proper way to do it as Ski points out.
What is the coupling diameter?
Typically a guideline is 0.001" out per inch of coupling diameter is OK. Of course closer is better and can usually be done.

Is there ANY movement in the lower nuts at all? 0.008 at the coupling may only need 0.001 or 0.002 drop at the engine front to at least get much closer.
The distance between the front and rear mounts will have an effect on how much the front really has to drop.
Checks done in water. I am not at boat but I think the coupling is probably 6" and shafts are 2"
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Old 12-21-2018, 04:03 PM   #14
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Originally Posted by jleonard View Post
Not necessarily.....My summer marina guys insist that near the upper end of the stud is better.

They are experienced in that, I am not.
I'm sure there are arguments either way.
Chevy or Ford I suppose (or should I say Toyota or Honda).

Near the upper end of the stud? That flies in the face of conventional wisdom, and most motor mount manufacturer instructions, better to be closer to the middle or lower (with room for adjustment) to reduce thrust leverage. The good news is if you are too high on the stud you can always add a shim.

Ski is right, under no circumstances should a final alignment be done when hauled, boats are far too flexible for this. The rule of thumb for coupling clearance is 0.001" per inch of coupling face diameter, so if the coupling was 6", a max of 0.006", if you are truly at 0.008 it's hardly worth changing, but if you are 0.008" over the max, that's worth correcting.

As an aside, and contrary to popular belief, because it's constant, misalignment is rarely the cause of vibration. Eccentrics cause vibration, a bent shaft, bent prop, off center coupling bore or pilot bushing etc. I've encountered many shafts that were so far out of alignment that they could not be turned by hand, and no vibration.

A two part article on alignment

https://stevedmarineconsulting.com/t...aft-alignment/

https://stevedmarineconsulting.com/t...nment-part-ii/
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Old 12-21-2018, 04:04 PM   #15
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Sorry, just saw your response about checks being done in the water.
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Old 12-21-2018, 04:06 PM   #16
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Originally Posted by Steve DAntonio View Post
Near the upper end of the stud? That flies in the face of conventional wisdom, and most motor mount manufacturer instructions, better to be closer to the middle or lower (with room for adjustment) to reduce thrust leverage. The good news is if you are too high on the stud you can always add a shim.

Ski is right, under no circumstances should a final alignment be done when hauled, boats are far too flexible for this. The rule of thumb for coupling clearance is 0.001" per inch of coupling face diameter, so if the coupling was 6", a max of 0.006", if you are truly at 0.008 it's hardly worth changing, but if you are 0.008" over the max, that's worth correcting.

As an aside, and contrary to popular belief, because it's constant, misalignment is rarely the cause of vibration. Eccentrics cause vibration, a bent shaft, bent prop, off center coupling bore or pilot bushing etc. I've encountered many shafts that were so far out of alignment that they could not be turned by hand, and no vibration.

A two part article on alignment

https://stevedmarineconsulting.com/t...aft-alignment/

https://stevedmarineconsulting.com/t...nment-part-ii/
Thanks Steve, BTW I have already read your articles several times. Good info
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Old 12-21-2018, 04:49 PM   #17
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.002" has been my standard since my dad, a chief engineer, taught me. I've fixed a lot of other peoples boats done to a looser standard. I owned more boats than I can list from memory, and several had many thousands of hours. In all that time, I only had to change one of my own bearings.
Depending on the motor mount, you can remove it and take some off the bottom/top, depending on the engine, take some off the engine, or take some off the engine bed.
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Old 12-22-2018, 09:31 AM   #18
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Thanks Steve, BTW I have already read your articles several times. Good info
OK, glad it was helpful. I often tell owners, even if you aren't doing the work yourself, it pays to understand how it should be done. This enables you to ask the right questions to vet a mechanic you are considering having do the work. If you get the wrong answers you can move on. Once the work starts, if you are monitoring you'll know if something's not being done right.

I was on a commercial project in Baltimore last week and was horrified to see a professional mechanic using a "bang nut", a bronze nut screwed to the end of a shaft that's repeatedly slammed with a maul, the shock from which separates the prop from the shaft. That shock is also conveyed into the transmission. It's a shortcut at best. Props should be removed using mechanical or hydraulic prop pullers.
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Old 12-25-2018, 09:30 AM   #19
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wouldnt a flex coupling between the tranny and the shaft allow for even more than .008 mis alignment?
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Old 12-26-2018, 06:32 AM   #20
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The use of a flexible coupling does not mean you can compromise alignment specs.




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wouldnt a flex coupling between the tranny and the shaft allow for even more than .008 mis alignment?
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