Motor Mounts and Shaft Coupling Alignment

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Motor Mounts and Shaft Coupling Alignment

Postby hansvillejohn on Sat May 11, 2019 6:07 pm

With my head upside down in the motor well of my 2017 R25sc, while checking out the stuffing box (it had been dripping at 1 drip per 10 seconds), I noticed and was shocked to see the back two motor mount nuts loose. The bottom nut had loosened 5/8" on starboard and 1/4" on port. I called Ranger and they said I should tighten them back up.
Why had they loosened on a boat with 80 hours on it??
I looked in my Don Casey book (This Old Boat) and set out to try adjust the engine to get the coupling plate gap to .004" tolerance. I got it pretty close adjusting the motor mount nuts for up and down, but there is too much gap side to side and that adjustment looks like a lot bigger job.
Now I'm super sensitive to vibration at different rpm's.
Should I stop worrying, or is this serious stuff?
John
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Re: Motor Mounts and Shaft Coupling Alignment

Postby NorthernFocus on Sat May 11, 2019 6:38 pm

hansvillejohn wrote:...Should I stop worrying, or is this serious stuff?

Like most things it depends. If alignment is out bad enough it can damage your transmission and/or wear out your cutless bearing. Also if it is bad enough to be causing vibration there can be all sorts of unpredictable things that shake loose or break.
Dan

Never confuse confidence for competence.
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Re: Motor Mounts and Shaft Coupling Alignment

Postby BB marine on Sat May 11, 2019 8:19 pm

Worry about it! .004 horizontal side to side and vertical up/down is ok but you really don't want it much worse then that. Side to side can be aligned by using the slots in the motor mounts. Once you have your vertical close then loosens the top motor mount nuts and slide the motor on the mounts. Sometimes you can move the front of the engine one way and the rear opposite. When doing this you must still maintain your parallel off set. It is tight in the compartment and it can take some time but it should be aligned properly.
Brian Brown
Cutwater 26
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Re: Motor Mounts and Shaft Coupling Alignment

Postby allanrs74@gmail.com on Sun May 12, 2019 8:15 am

John,

I had a very similar situation on my 2016 R-27 C last June in the wild's of Canada, south of Buttedale, BC. The boat/engine had 200 +/- hours on it and we were cruising along at 3000 RPM very nicely, dodging lots of debris in the water. Instantly, we heard a loud bang and severe vibration of the engine/transmission began. I took the boat out of gear and looked behind in my wake to try to see what debris I had hit. But I could see nothing in my wake so I suspected I'd hit a submerged log (dead head) which can happen. Putting the boat in gear caused unacceptable vibration at any RPM. I hailed a passing 36' Albin who kindly towed us into Buttedale for the night. I arranged on the sat phone a 100 mile +/- tow into Prince Rupert, BC for the next day. The VolvoPenta dealer in Prince Rupert hauled the boat and we removed the shaft and propeller to check for damage/balance/straigtness. There was not a scratch on the prop and the shaft was perfect. While reinstalling the shaft and prop, the mechanic doing the work mentioned " Oh yah, I noticed that the shaft and transmission coupling were very misaligned when I disconnected them". So he took the time to realign the engine/shaft and the boat continued to run just fine on the remainder of my trip to Seward, AK. After thinking about the situation and speaking to several knowledgable people, we suspect that the rear motor mount lower nuts backed off some and the engine 'hung' in place until it instantly dropped into an unaligned position causing the severe vibration.

One very, very important thing I learned and will pass onto everyone in the community is that when you tow a Ranger Tug with a Volvo Penta D3 - 200 which is not running you have to shut the sea water intake (sea cock). If you don't, you can and will 'hydrolock' your engine. This occurred during my tow and required taking the top of the engine off, removal of the turbo and drying everything out. There is no mention of this in the Volvo Penta or Ranger Tug operating manual which I have brought to the attention of Fluid Motion and I think is a huge oversight. I have made a simple 'notice tag' in red and hung it on my sea cock to avoid this in the future.

Bob Allan
Annie M R 27C
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