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Old 11-08-2022, 18:16   #1
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Prop shaft coupling

Diagnosing a vibration, I found a bolt got loose on the prop shaft coupling (not sure what exactly it is called, see photo). I put it back and then noticed the others were loosish too. Probably a stupid question but how tight should these be? Hand tightened, tightened well, left a little loose for some reason?
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Old 11-08-2022, 20:57   #2
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Re: Prop shaft coupling

I just did an engine/shaft realignment on my Yanmar 3JH4E on my Beneteau. Your setup looks similar to mine but it looks like your shaft is turning and the bolts are blurred in the picture. The 4 bolts/nuts on mine are 12mm 304 steel with nylon locknuts tightened with loctite (blue). Once aligned I tightened the bolts alternatively and gradually to ensure an even tight fit. I didn't use a torque wrench but instead tightened "really well".

BTW...if your bolts were loosish and there is vibration chances are you may have an alignment issue. Easy to check with a $5 feeler gauge.
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Old 12-08-2022, 04:04   #3
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Re: Prop shaft coupling

Manufacturers web site probably has instructions and specs. Bake sure the flex element is not damaged
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Old 12-08-2022, 04:50   #4
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Re: Prop shaft coupling

Quote:
Originally Posted by Nicholson58 View Post
Manufacturers web site probably has instructions and specs. Bake sure the flex element is not damaged
What is flex element?
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Old 12-08-2022, 05:05   #5
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Re: Prop shaft coupling

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Originally Posted by Tenedos View Post
What is flex element?
Doesn't look like you have one. There are a couple different kinds but most common is a plastic disc between the coupling halves.
I wonder about the marks on the shaft about an inch behind the coupler. They often put a score mark where the shaft meets the coupler so you can see if it moves. Possibly the shaft is not all the way into the coupling. If you went into reverse with the set screws loose the shaft could have backed out. Easy check, unbolt the coupling halves and feel inside to make sure the end of the shaft is flush or nearly flush with the coupling face. Also, can't tell on the photo because the shafts appears to be turning, if there are set screws tapped into the side of the coupling, there should be dimples drilled into the shaft for them to notch into. Better than just screw tension on the smooth surface to hold the shaft in place. Unless it's a double tapered shaft with a nut on the inside to hold the shaft, there are no set screws on those.
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Old 12-08-2022, 05:18   #6
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Re: Prop shaft coupling

Was the photo taken while the shaft was spinning?
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Old 12-08-2022, 07:07   #7
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Re: Prop shaft coupling

Here is a photo when it is stationary
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Old 12-08-2022, 07:43   #8
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Re: Prop shaft coupling

Those bolts should be very tight.

Those look like stainless bolts. In a normal installation, those would NOT be stainless steel bolts, and they should have lock washers (which I can not see in your picture) so they do not come loose! Guessing they are 5/16" bolts, a standard Grade 1 carbon steel bolt would be torqued to 7.5 ft-lbs, stainless would be 12 ft-lbs. If it was my boat, I'd use a fine thread Grade 5 or better bolt and increase the tightening torque appropriately.

If your bolts have come loose, an engine alignment should be done. If the engine is in proper alignment with the shaft, it would spin pretty smoothly even with loose bolts. This is important, a badly aligned engine can destroy LOTS of parts of the drive train.

Using stainless bolts without lockwashers in this application tells me that whoever did it last didn't really know what they were doing. That alone would trigger me to do an engine alignment and a complete check of the whole shaft system--if it was my boat.

See capt-jgw's comments above...
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Old 12-08-2022, 08:00   #9
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Re: Prop shaft coupling

Quote:
Originally Posted by Tenedos View Post
Here is a photo when it is stationary
Really needs lock washers of some type, Loctite, at the very least.
The scuff marks are curious.
I'd slide the Coupler back, and check.
The shaft as mentioned could have slipped back a bit.
Is this a pressed fit, as I don't see set screws or a bolt, sometimes there's a bolt on the end of the shaft when you slid the shaft back you may check for that.

Locktite those bolts, do recheck the coupler face alignment.
Shouldn't be more than .003 gap at each 90 degree measurement.
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Old 12-08-2022, 09:17   #10
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Re: Prop shaft coupling

Don’t second guess. Find the manufacturer’s assembly instructions. Not rocket science. If all else fails, read the instructions.

My 2 cents, if this is a rigid coupling then probably the bolts should be tight. I’d use blue Loctite.

You have the technology. Don’t listen to us geezers. Read the instructions.
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Old 12-08-2022, 09:36   #11
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Re: Prop shaft coupling

Quote:
Originally Posted by Nicholson58 View Post
Donít second guess. Find the manufacturerís assembly instructions. Not rocket science. If all else fails, read the instructions.

My 2 cents, if this is a rigid coupling then probably the bolts should be tight. Iíd use blue Loctite.

You have the technology. Donít listen to us geezers. Read the instructions.
Looking at the pictures helps.
This has no flex isolation plate.

A standard, coupling is simple to install.
This is very standard.
Check the coupling faces for misalignment.
Locktite the bolts, fit lock washers if you can.
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Old 12-08-2022, 09:36   #12
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Re: Prop shaft coupling

Correct torque depends on what size, material and thread pattern the bolts are.


Torque to the proper spec for the bolts you are using.



BTW, grade 8 fine thread is pretty common.
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Old 12-08-2022, 10:37   #13
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Re: Prop shaft coupling

Quote:
Originally Posted by Boatyarddog View Post
Looking at the pictures helps.
This has no flex isolation plate.

A standard, coupling is simple to install.
This is very standard.
Check the coupling faces for misalignment.
Locktite the bolts, fit lock washers if you can.
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Boatyarddog is correct.

My Beneteau documentation does not have any instructions for coupler install or removal. If you have one for your Jeanneau please post it for us Beneteau / Jeanneau owners. Much appreciated.

The coupler should have a large nut (24mm?) inside attaching it to the shaft. If you can, make sure it is tight.

The scoring on your shaft is likely from a hose clamp that was used at some point (for maintenance / installation?) and has since been removed. I would not worry about it. Shaft markings for measurement purposes are usually made with a Sharpie.

Most anything related to your drivetrain is metric. Note markings on the face of your bolts. I take pictures with my phone and then zoom in to be able to see all markings. Google them and you will see what you have. Your bolts look to be factory installed. Replace your nuts with the correct locking nuts. Apply blue loctite. Apply even, very tight pressure all around. Don't overtighten.

Your loose bolts and vibration may pose a very serious problem if not addressed properly.

If you are not 100% comfortable doing this hire a professional.
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Old 12-08-2022, 14:25   #14
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Re: Prop shaft coupling

but how is the shaft linked to the coupler?
this one is not split, no external tightening...
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Old 12-08-2022, 14:37   #15
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Re: Prop shaft coupling

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Originally Posted by bil56 View Post
but how is the shaft linked to the coupler?
this one is not split, no external tightening...

From the picture, we DON'T know.



Perhaps rotating it would reveal a set screw???
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