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Old 02-10-2019, 00:08   #1
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Shaft alignment with flexible coupling

Hi all,

Next week i will be lifting the donk back onto the shiny new engine mounts. Having read as much as i could find on the topic of engine to shaft alignment i am still a bit perplexed as to what might be the best way to approach a flexible coupling scenario.

On the shaft is a "type6" Vetus flexible coupling which i am hesitant to completely remove; and do i even need to remove it?.

I'm thinking maybe that i could construct a metal plate with 4 holes to place over the bolts shown, then with bushes tighten it down so it will be exactly parallel to the internal Vetus flange. Then aligning that face to the transmission flange with feeler gauges ??? Am i on the right track, or making this way more difficult than it needs to be?

Please any thoughts much appreciated
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Old 02-10-2019, 02:12   #2
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Re: Shaft alignment with flexible coupling

just use a micrometer between the prop shaft flange face and the output flange with the prop shaft secured so it can't move back.
as well as a set square to check for paralele misalighnment.
do this by turning the output flange in 90deg increments and checking 0deg,90deg,180deg,270deg,it will soon become apparent what adjustments need to be made
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Old 02-10-2019, 03:55   #3
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Re: Shaft alignment with flexible coupling

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Originally Posted by atoll View Post
just use a micrometer between the prop shaft flange face and the output flange with the prop shaft secured so it can't move back.

Micrometer? Or feeler gauge?
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Old 02-10-2019, 04:08   #4
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Re: Shaft alignment with flexible coupling

The purpose of the Vetus Type 6 flexible coupler is to tolerate misalignment between the engine and the output shaft.

It is best to adjust for best alignment between the parts.

The conical clamping hub permits coupler movement to the shaft of the parts shown in the first image.

A pair of small 123 blocks could be used to position the coupler half face in the first image to be perpendicular to the shaft. Once block placed on the shaft, to get the back side above the conical clamping hub, then the second block to get the back side of the coupler perpendicular to the shaft.

Then feeler gauges between the coupler faces and vernier calipers around the perimeter would permit setting the motor mounts for correct vertical, lateral and angular alignment.

https://www.vetus.com/media/magentom...09103940_0.pdf
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Old 02-10-2019, 05:44   #5
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Re: Shaft alignment with flexible coupling

Don't forget to lubricate the conical clamping hub w/ the Molykote grease specified in the Vetus link.

The universal joint grease looks like it has started drying out. It might be useful to replace it w/ the correct / fresh grease at this time. Vetus could assist w/ identification of the correct lubricant.
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Old 02-10-2019, 10:04   #6
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Re: Shaft alignment with flexible coupling

I have read, in my engine's installation manual, that a flexible coupling should not be used with flexible engine mounts. Either the engine is rigid mounted with a flexible coupling, or the engine has flex mounts with a rigid shaft connection, but not both flexible. I personally don't know enough about it to say; perhaps someone who knows can comment?

Greg
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Old 02-10-2019, 10:07   #7
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Re: Shaft alignment with flexible coupling

Is the boat in the water or out on the hard? Whatever alignment you do while the boat is out of the water will need to be checked once the boat is back in the water.
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Old 02-10-2019, 11:36   #8
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Shaft alignment with flexible coupling

Quote:
Originally Posted by CarinaPDX View Post
I have read, in my engine's installation manual, that a flexible coupling should not be used with flexible engine mounts. Either the engine is rigid mounted with a flexible coupling, or the engine has flex mounts with a rigid shaft connection, but not both flexible. I personally don't know enough about it to say; perhaps someone who knows can comment?

Greg


There is logic in that as you could get an oscillation going that should be RPM dependent if you do.
But I think many, many boats have both with no problems.
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Old 02-10-2019, 13:48   #9
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Re: Shaft alignment with flexible coupling

Does your shaft have a carrier bearing?
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Old 02-10-2019, 19:38   #10
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Re: Shaft alignment with flexible coupling

Quote:
Originally Posted by singlespeed View Post
Is the boat in the water or out on the hard? Whatever alignment you do while the boat is out of the water will need to be checked once the boat is back in the water.
Timber or glass always in the water, Steel boat is optional. good luck
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Old 03-10-2019, 00:52   #11
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Re: Shaft alignment with flexible coupling

[QUOTE=wingless;2988406]The purpose of the Vetus Type 6 flexible coupler is to tolerate misalignment between the engine and the output shaft.

It is best to adjust for best alignment between the parts.

The conical clamping hub permits coupler movement to the shaft of the parts shown in the first image.

A pair of small 123 blocks could be used to position the coupler half face in the first image to be perpendicular to the shaft. Once block placed on the shaft, to get the back side above the conical clamping hub, then the second block to get the back side of the coupler perpendicular to the shaft.

Then feeler gauges between the coupler faces and vernier calipers around the perimeter would permit setting the motor mounts for correct vertical, lateral and angular alignment.

Thanks Wingless, that method sounds like it would work nicely.....123 blocks i had never heard of, but do now thanks to your input and google

[QUOTE=wingless;2988437]Don't forget to lubricate the conical clamping hub
The universal joint grease looks like it has started drying out. It might be useful to replace it w/ the correct / fresh grease at this time. Vetus could assist w/ identification of the correct lubricant.

yes thanks i will after cleaning it up, and i'll do a search for the grease online.

Quote:
Originally Posted by singlespeed View Post
Is the boat in the water or out on the hard? Whatever alignment you do while the boat is out of the water will need to be checked once the boat is back in the water.
It's in the water and i'm not sure whether there is a bearing in the stern tube. I will pull the shaft out in about 6 months in any case as i'm up for some major works including the cutlass bearing. So with the shipwrights help the shaft and motor can be more precisely lined up on the hard. Just hoping that my alignment effort is good enough to not damage anything in the meantime

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Old 03-10-2019, 05:25   #12
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Re: Shaft alignment with flexible coupling

Quote:
Originally Posted by wingless View Post
The purpose of the Vetus Type 6 flexible coupler is to tolerate misalignment between the engine and the output shaft.

It is best to adjust for best alignment between the parts.

The conical clamping hub permits coupler movement to the shaft of the parts shown in the first image.

A pair of small 123 blocks could be used to position the coupler half face in the first image to be perpendicular to the shaft. Once block placed on the shaft, to get the back side above the conical clamping hub, then the second block to get the back side of the coupler perpendicular to the shaft.

Then feeler gauges between the coupler faces and vernier calipers around the perimeter would permit setting the motor mounts for correct vertical, lateral and angular alignment.

https://www.vetus.com/media/magentom...09103940_0.pdf
Quote:
Originally Posted by Wayfarer111 View Post
Thanks Wingless, that method sounds like it would work nicely.....123 blocks i had never heard of, but do now thanks to your input and google
You're welcome.

Quote:
Originally Posted by wingless View Post
Don't forget to lubricate the conical clamping hub w/ the Molykote grease specified in the Vetus link.

The universal joint grease looks like it has started drying out. It might be useful to replace it w/ the correct / fresh grease at this time. Vetus could assist w/ identification of the correct lubricant.
Quote:
Originally Posted by Wayfarer111 View Post
yes thanks i will after cleaning it up, and i'll do a search for the grease online.
Good plan.

The online search didn't reveal the specific Molykote grease for me, just the dozens of available options, so a call may be required.
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Old 05-10-2019, 01:17   #13
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Lightbulb Re: Shaft alignment with flexible coupling

Been having a few more thoughts on this alignment. I possess a large steel set square (700x500mm)

Could i not remove the Vetus flexible coupling, pull the shaft forward until almost touching the transmission, adjust engine mounts to get the position right....well for the tranny at least.

With the long side of the square along the shaft (fixed in place) and the other against the tranny flange, rotate the tranny flange and check the differences with a feeler gauge. then adjust the mounts for alignment, and small re-adjustment for position.

Does this sound plausible as i am effectively using the square as a temporary rigid flange for the shaft?
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Old 05-10-2019, 02:06   #14
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Re: Shaft alignment with flexible coupling

This image shows the objective.

No, removing the flange will only permit a gross alignment.

A correct fine alignment is only possible w/ the flange in-place.


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Old 05-10-2019, 02:44   #15
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Re: Shaft alignment with flexible coupling

Quote:
Originally Posted by wingless View Post
This image shows the objective.

No, removing the flange will only permit a gross alignment.

A correct fine alignment is only possible w/ the flange in-place.


Agreed. Nice diagrams.

They show why the usual feeler gauge method only measure 'angular misalignment'.
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