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Old 10-11-2014, 08:11 PM   #1
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Flexible couplings to correct misalignment

I've been living (and cruising!) with a shaft misalignment problem going back to when my Willard was repowered in 2007. Presently, the aft end of the engine oil pan is touching the concrete ballast below. I need to raise the engine at least an inch but this will only increase the misalignment between gear flange and shaft. Has anyone installed a flexible coupling that can handle prop trust and correct for misalignment? I started with Aquadrive, but too expensive. I have also considered swapping the velvet drive gear for a down-angle ZF tranny with a dropped output shaft...also expensive and labor intensive.

At the moment I'm considering the Marine Joint (an actual CV joint) made by Powertrain Industries based in the Netherlands. Here is a blurb about the Marine Joint: "A super flexible coupling for use between marine transmissions and propeller shafts. The technology is based on the standard front wheel drive joint on cars. Very simple and quick installation with a significant reduction of noise. Takes up to 8." Is anyone using one of these...or a CV joint between gear and shaft WITHOUT a trust bearing a la Aquadrive?
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Old 10-11-2014, 08:14 PM   #2
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Flexable couplings don't correct misalignment.

You need to have your engine properly aligned.

Aqua Drives or similar rely on a perfectly (within reason) aligned thrust bearing.
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Old 10-11-2014, 08:51 PM   #3
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I agree with Eric. Get a jack hammer and bust out enough concrete to align the prop shaft properly.

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Old 10-12-2014, 02:00 AM   #4
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I just read an article on flexible couplings, the facts were that the flex coupling does not correct the issue of misalignment. I thought it was in one of the last couple of months of Passagemaker, could have been in Cruising World though. Google that... I had great luck cutting concrete with an angle grinder and a concrete wheel. Much more gentle than a jackhammer, a bit dusty though.
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Old 10-12-2014, 02:55 AM   #5
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David, I wish it was that simple :-) The rear motor mounts are already maxed out at their lowest point and still the engine needs to come down a tad more. It seems the practical solution is to raise the engine and resettle it on the motor mounts, then use a CV joint to take up the vertical offset between the transmission and the shaft. I asked about the Powertrain Marine Joint because it seems to be the only marine CV joint available that can absorb thrust from the propeller. Their is also the Thompson CV Joint which can take thrust and axial loads but it costs around $5,000! I'll be meeting with a propulsion mechanic next week and hopefully we'll settle on a permanent fix, even if it means installing an Aquadrive type solution.
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Old 10-12-2014, 07:31 AM   #6
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How about raising the engine, taking off the oil pan and having the oil pan modified in that back corner or section?

If the loss of oil volume isn't too great...big deal...if it's more than you like, add a second remote oil filter on if possible...

May not work...just thinking outside the box.
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Old 10-12-2014, 07:37 AM   #7
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Greetings,
Mr. ps. Could be wrong here but the sense I get is the problem at this point is that there is not enough downward adjustment left in the mounts to allow alignment. Oil pan interference is secondary so I expect new mounts that allow more downward adjustment along with concrete removal or as you suggest, oil pan modification is the "best" although not easiest solution.
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Old 10-12-2014, 07:52 AM   #8
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I assume raising the front doesn't achieve the preferred effect?

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Old 10-12-2014, 07:54 AM   #9
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With modest misalignment a single shaft U joint is sometimes used . Fairly inexpensive.

They are OK at the modest thrust of most 40-50 hp diesels , though they do take up space on the drive shaft.

If you want to try , I have one for a 1 3/8 shaft that might be fitted.

Also Beware it was not uncommon for a boat designer and builder to Offset the engine by up to 5 deg so the prop walk would be neutralized at cruise , no rudder drag going straight.

Many folks do not know this and install a re engine on center line , much ungood.
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Old 10-12-2014, 07:59 AM   #10
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Thanks RT...I was focused on the original post and oil pan touching.

Lower the mounts and modify the oil pan...without pics or seeing it ...all mod suggestions are shots in the dark..

Otherwise just get on with a universal joint of some kind or new drop tranny if the engine can't be lowered....(probably can though)....
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Old 10-12-2014, 11:06 AM   #11
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nwboater,
First of all whoever did the install needs to be held accountable.

You wrote "The rear motor mounts are already maxed out at their lowest point and still the engine needs to come down a tad more."

Did the installer tell you this installation was not possible? Or has the installer told you to take a hike? Seems if they did their job correctly and told you it wouldn't fit you wouldn't have this problem. Was it their incompetence or did you tell them to install it anyway?

Seems to me the only proper fix is to;

A. Find mounts that allow lower adjustment and remove some ballast.
B. Modify the oil pan and get lower mounts.
C. Cut down your engine beds.
D. Fabricate new engine mount flanges that lower the engine using the original mounts.
E. a combination of the above.

I have plastic engine mounts in Willy and perhaps due to the way the're made they may permit lower engine installation. The mounts I have are from Poly Flex. They are made in Australia but available to you right across the border in lower mainland BC.

And all should be done free to you if they did this and presented their work as good. This isn't North Island is it? I hope I never find my boat in this yard.

Removing that amount of ballast will not be difficult but of course the engine will need to be "moved". I had all the ballast in the Lazerette removed from our boat.
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Old 10-12-2014, 11:21 AM   #12
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Move the entire engine forward a couple of inches. Buy a new longer propeller shaft, realign everything, and walla you are done.

Alternately a flexiple coupling would add about an inch to inch and a half to the shaft so just move the engine forward and add the coupling and realign.
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Old 10-12-2014, 12:51 PM   #13
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Note that most cv joints cannot take thrust, so if using one a thrust bearing must be installed between shaft and cv joint. This includes adding a very robust structural member to absorb thrust loads, and this includes possible impact loads from grounding or other prop strikes.

Ujoints can absorb thrust, but not side loads unless specifically designed for that. Most are not. A change in angle with a thrust load creates a side load, so this must be considered.

My vote is to chip out/grind out some concrete and modify rear mounts/brackets to get things lined up.
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Old 11-18-2014, 06:21 PM   #14
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It was five weeks ago that I posted my dilemma regarding shaft alignment and vibration in my single engine trawler...Problem identified and fixed! Northstar now runs smooth and is vibration free. Turns out the prop shaft was "low in the tube" and had been this way since it was repowered in 2007. With the shaft centered in the stern tube it was evident that the block needed to be raised on the mounts--NOT lowered! The engine now sits a good inch off the bottom and no part of the block is touching the hull. The guys at Pacific Marine Center, Anacortes did the fix, along with a few other maintenance items for a fair price. Northstar is now back in her covered slip ready to slumber for the winter while we're warming our bones in Mexico. I'm very grateful that this yard insisted on hauling the boat and inspecting all parts of the running gear, starting with the propeller...I can only wonder why the diesel shop I hired to do the repower back then couldn't figure this out?!? Btw, I have asked them to reimburse me for half the cost of this repair -- do you think I'll hear back?
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Old 11-18-2014, 07:31 PM   #15
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I doubt you'll hear from them or they won't take responsibility. Either way, the important part is your boat is right.

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Old 11-20-2014, 04:26 PM   #16
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I also have a bit of misalignment. I tried to get North Harbor to come out but I guess my boat is too old or my money is not green enough as they just never showed up on the scheduled date/time. No call, nothing.

Good to know Pacific Marine did a good job. I will contact them. Olympic propeller did my prop and he said I should call Pac Marine also

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