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Author Topic: Shortening the drive shaft for new transmission  (Read 408 times)

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kable

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Shortening the drive shaft for new transmission
« on: July 16, 2022, 10:26:05 PM »

So for most transmission replacements you have to move the drive shaft back a bit 1" to 1.5".

How does one do this?

A couple years ago when replacing my cutlas bearing I ended up getting a new stainless drive shaft and sent the prop off to get everything tuned etc.  Then added new dripless and coupled against the transmission.

I don't think I can push the shaft back any further because it already looks like the gap between the strut and the prop is at or exceeding the 1" max.  So I probably need to cut it.  How does one cut this, in place, in the water?

I also need to potentially raise my engine up a bit.  How do you do that, I assume some type of shim, but what is that specifically?

Here is a pic of my current coupler.  I assume I don't have a 'flexible coupling'.  Should I get one?  I am worried about not getting everything all aligned after the install and it seems like this may help.

Thoughts?
« Last Edit: July 17, 2022, 10:12:21 AM by kable »
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1988 C34 #785 SR/WK Universal M25XP - "As We Wish" Bellingham, WA - San Juan Islands

Kyle Ewing

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Re: Shortening the drive shaft for new transmission
« Reply #1 on: July 17, 2022, 05:23:50 AM »

The red part on the coupler looks like a "Globe Drivesaver". If so you could remove it to get space back. It's not a true "flexible coupling" but more of a shock absorber if your prop hits something.  I have one. 

Raising the engine should be easy as long as the mounts have enough thread.  It looks like you're engine is pretty low so raising it 1/4 or more should not be an issue.

The only way I know of shortening the shaft is to remove it and send to a shop  The risk of too long a shaft is prop shaft whipping (which could damage the shaft) if your prop is out of balance .  How much vibration do you have today? 

How long is too long?  Hard to say. You'll find many boats in the yard with"too long a shaft" which have no problems. 

This is an excellent article regarding engine alignment: https://www.yachtsurvey.com/Alignment2.htm


 

 
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Kyle Ewing
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kable

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Re: Shortening the drive shaft for new transmission
« Reply #2 on: July 17, 2022, 09:57:59 AM »

If I removed the Globe Drivesaver, that may give me space back but probably not exact.  So I would have to still 'move' the shaft back or forward to connect everything.  Can you just move the shaft through the dripless PSS?  Safely in the water?  I have seen something about scratching?

How much vibration do I have?  It is sure hard to say because this is my first boat like this.
I have the 'some RPMs' are worse than others but I don't have things in the cabin rattling or I can't feel it in my feet etc.
It seems to have gotten louder (vibration/engine/trans/??) over the last couple years.  So I am replacing the motor mounts and insulation during this.

The prop, shaft and globe drivesaver coupler were all machined and balanced 2 year ago.

I have also see this, what does this mean?
Quote
This maybe a problem if you use the keyway shaft to transmission attachment.  If that is a problem change to flexible coupling that doesn't need a keyway -Ron
What is a keyway?
« Last Edit: July 17, 2022, 10:15:36 AM by kable »
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1988 C34 #785 SR/WK Universal M25XP - "As We Wish" Bellingham, WA - San Juan Islands

KWKloeber

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Re: Shortening the drive shaft for new transmission
« Reply #3 on: July 17, 2022, 10:21:18 AM »

@Kable

I noticed that the anodes might be in a location for "shaft whip."  Not the worst (mid-span) but IIWMB I'd place them 2 diameters from the strut and hull.
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kable

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Re: Shortening the drive shaft for new transmission
« Reply #4 on: July 17, 2022, 10:59:13 AM »

Thanks, will have the diver do that next time.
Assuming I don't have to pull the boat to make these shaft adjustments for a new transmission.

I guess I am hoping that I can remove the drive saver and coupling.  Add in a federal flex and be about the same but then I still have to move the shaft through the PSS and what will that do, can you do it?

Then I still will be left w/ too much post the strut (according to these forums) and now the anodes.

The original length (before I moved to stainless) looks too long as well, but better than my current.

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1988 C34 #785 SR/WK Universal M25XP - "As We Wish" Bellingham, WA - San Juan Islands

Ron Hill

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Re: Shortening the drive shaft for new transmission
« Reply #5 on: July 17, 2022, 11:10:15 AM »

Kyle : What I'd do is get rid of the Driver Saver and get a flexible coupling. I'll guess that when you cut the shaft (so it's 1" space from the from of the prop to the rear of the strut) you'll be out of "keyway" on the shaft.  The flexible coupling doesn't need a key way. 

I see that you have the original engine mounts - I'd get some new Vetus 75 engine mounts and realign the engine  -  then you should be OK.  That will raise the engine!!

You should be able to do everything in the water.  I used a Saws-all to cut my shaft.  The shaft should slide along the inside of your dripless gland.

A few thoughts
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Noah

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Re: Shortening the drive shaft for new transmission
« Reply #6 on: July 17, 2022, 11:28:36 AM »

Ron- you cut a Stainless Steel shaft with a sawzall while in the water and with the engine in place?? “Brave” operation!
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KWKloeber

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Re: Shortening the drive shaft for new transmission
« Reply #7 on: July 17, 2022, 11:33:32 AM »


cut a Stainless Steel shaft with a sawzall while in the water and with the engine in place?? “Brave” operation!


He didn't have AC to run the saw so he just ran the engine and held the blade against the shaft!   :rolling :rolling :rolling
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
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Ron Hill

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Re: Shortening the drive shaft for new transmission
« Reply #8 on: July 17, 2022, 12:46:53 PM »

Noah : I never said where I was, but Ken has a new way!!!  Even harder to do if you are in reverse!!  :shock:

A thought
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kable

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Re: Shortening the drive shaft for new transmission
« Reply #9 on: July 17, 2022, 05:55:15 PM »

Sorry for the dumb questions...

So the boat is in the water, I can't see or measure the distance from the prop to the strut (I do have the pics posted but no measurements).

I understand I can remove the drive saver and add the Federal flex coupler and then I will be 'too long' w/ the new transmission.  So I could cut off the end (engine side) before adding the couplers etc.  If I go this route, I don't need to move the shaft back at all, just cutting the end, right?  But this doesn't 'help' the fact that maybe I have too much distance between prop and strut.

So should I go-pro, dive and measure, then pull shaft forward to the engine, then measure (no drive save + fed coupler - new trans) and cut?
Sounds like moving through the dripless isn't a concern, no issues moving through the cutlas? (2 years old)

Ron you have made these cuts in the water, Noah and KWKloeber (Ken?) you joke/pushed back on this idea.  What are the concerns/things to consider.

Just trying to learn...
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Noah

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Re: Shortening the drive shaft for new transmission
« Reply #10 on: July 17, 2022, 06:46:23 PM »

IMO it seems like a risky maneuver to try inside the boat while in the water. Especially if you plan on keeping the cut shaft once cut. A sawzall is not a precise tool and can be dangerous to control in a confined space cutting tough metal. Ideally haul the boat, measure, remove shaft, and cut—either yourself, or preferably take to a machine shop.
« Last Edit: July 17, 2022, 07:04:09 PM by Noah »
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waughoo

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Re: Shortening the drive shaft for new transmission
« Reply #11 on: July 17, 2022, 06:58:27 PM »

The other thing that hasnt been said is that the compression of the bellows on the dripless shaft seal goes away when the shaft isnt connected to the engine risking water intrusion while in the water.
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KWKloeber

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Re: Shortening the drive shaft for new transmission
« Reply #12 on: July 17, 2022, 07:33:12 PM »

>>>Ron you have made these cuts in the water, Noah and KWKloeber (Ken?) you joke/pushed back on this idea.  What are the concerns/things to consider.<<<

Read it carefully, he said YOU should be able to do it in the water. He said only that he cut it in place (not necessarily in the water.)
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
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Explore.  Dream.  Discover.   -Mark Twain

KWKloeber

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Re: Shortening the drive shaft for new transmission
« Reply #13 on: July 17, 2022, 07:35:41 PM »

Even IF IT could be cut in the water, what's Plan B (one ALWAYS NEEDS a B) if things go south?
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

Kyle Ewing

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Re: Shortening the drive shaft for new transmission
« Reply #14 on: July 17, 2022, 09:24:42 PM »

Sorry for the dumb questions...

So the boat is in the water, I can't see or measure the distance from the prop to the strut (I do have the pics posted but no measurements).

I understand I can remove the drive saver and add the Federal flex coupler and then I will be 'too long' w/ the new transmission.  So I could cut off the end (engine side) before adding the couplers etc.  If I go this route, I don't need to move the shaft back at all, just cutting the end, right?  But this doesn't 'help' the fact that maybe I have too much distance between prop and strut.

So should I go-pro, dive and measure, then pull shaft forward to the engine, then measure (no drive save + fed coupler - new trans) and cut?
Sounds like moving through the dripless isn't a concern, no issues moving through the cutlas? (2 years old)

Ron you have made these cuts in the water, Noah and KWKloeber (Ken?) you joke/pushed back on this idea.  What are the concerns/things to consider.

Just trying to learn...

Kable and all,

My experience is that the coupler end of the shaft has a keyway and dimples for the coupler set screws. If so, how can the shaft be shortened without extending the keyway and redrilling the dimples? Does the pictured coupler connect to the shaft in a different way?

Regarding zinc placement, make sure the diver doesn't place it so close to the strut that the shaft doesn't slide back far enough to work on.

I was paranoid about losing the shaft out the rear while working on it so I placed my zinc to act as a stopper so the shaft doesn't slide so far back that I can't get it back.

Kyle

 


« Last Edit: July 17, 2022, 09:30:58 PM by Kyle Ewing »
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Kyle Ewing
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