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Old 17-07-2018, 15:14   #1
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Prop shaft involuntary decoupling from engine

Dear community,

After a day of sailing the SF Bay with my Cal 2-27 (1977) I turned on my Atomic 4 gasoline inboard engine to proceed with lowering my sails. However, when putting it in gear I noticed something was wrong and after investigating I figured out that the prop shaft had come out of the engine/coupler. The shaft didn't completely depart the boat (most likely because a shaft zinc obstructed a complete departure).

After docking my boat under sail in the Berkeley Marina (great learning experience) I continued the investigation. My guess is that the set screw somehow came undone. I was able to reinsert the shaft into the coupler and tightened the setscrew into the dimple on the shaft.

Unfortunately, 2 trips later, the same thing happened. This time I decided to apply Loctite to the setscrew to (hopefully) keep the shaft in place and prevent it from coming out.

Since reinstalling the shaft in the coupler and using the Loctite I have only taken the boat out for a sail once. On this trip, I only used the engine for about 10 minutes (leaving and entering the marina). The shaft is still connected to the engine and did not come undone this time.

However, I'm still a little insecure about the situation. Does anyone have suggestions about how to prevent my shaft from coming out of the engine again?

Is it true that it is only the set screw what keeps the shaft from not falling out?
Is the application of Loctite to the set screw sufficiently effective in keeping the shaft in place?
What other (additional?) measures could I take to prevent the shaft from coming undone?

Thank you.
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Old 17-07-2018, 15:42   #2
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Re: Prop shaft involuntary decoupling from engine

Unless you have a split flange, the fact that the shaft is sliping out indicates that the coupler is worn and needs replacing. Get a split clamping style coupler that way you are relying only on the set screw to hold everything in place. The clamp style couplers have pinch bolts on either side (and a set screw) to clamp the coupler to the shaft. much better arrangement.

Something like this:

https://www.asap-supplies.com/us/pro...r-shaft-808416
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Old 17-07-2018, 15:48   #3
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Re: Prop shaft involuntary decoupling from engine

You could buy a flange with a pinch bolt, they're not that $$. And/Or drill the dimple for the set screw deeper with safety wire and locktite.
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Old 17-07-2018, 21:47   #4
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Re: Prop shaft involuntary decoupling from engine

Quote:
Originally Posted by Ecos View Post
You could buy a flange with a pinch bolt, they're not that $$. And/Or drill the dimple for the set screw deeper with safety wire and locktite.


Thatís what I did when the prop backed itself out when docking and I heard the bulge pump running.
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Old 17-07-2018, 23:34   #5
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Re: Prop shaft involuntary decoupling from engine

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Old 18-07-2018, 08:41   #6
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Re: Prop shaft involuntary decoupling from engine

Had this problem with my old Columbia 43. As per the previous post.
1. Deepen the dimple in the shaft (2x)
2. Longer set screw
3. Hole in the set screw with safety wire, so it can't turn
It lasted for the next 9 yearsthat I owned the boat.

I have a friend that drilled straight through the shaft and ran a bolt through instead of the set screw, but I think thats overkill, and may weaken the shaft.
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Old 18-07-2018, 09:00   #7
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Re: Prop shaft involuntary decoupling from engine

After putting shaft fully back in the coupler the first thing I would do is check the engine alignment. If it is out of line and vibrating too much doesn't matter how you fasten the shaft and set screw. It will lead to the failure of something else in the system - shaft, cutlass bearing, prop, or transmission.
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Old 18-07-2018, 09:48   #8
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Re: Prop shaft involuntary decoupling from engine

If you have a single rudder, the prop could move back far enough to jam it, and then you are in serious trouble. Put a hose clip round the prop shaft, half an inch in front of the stern gland, to limit how far back the shaft can move. Low cost insurance!

If you have a twin rudder, the prop shaft can leave the boat altogether, leaving a fairly large hole for water to come through. This hapened to a friend, twenty miles from the nearest land. Fortunately he had a bottle of champagne on board, so he opened it, quickly, and trust the cork into the hole, and drank the contents while he sailed home. Really.
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Old 18-07-2018, 11:42   #9
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Re: Prop shaft involuntary decoupling from engine

2 setscrews 90 degrees offset will stop any wiggle of the shaft in the coupler which is not assured with a single setscrew.It's the wiggle that makes it back out.
It costs almost nothing to add the extra setscrew before you decide ( and might actually preclude) spending bigger bucks on a new, different style coupler.
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Old 18-07-2018, 12:28   #10
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Re: Prop shaft involuntary decoupling from engine

Need to wire it..... seize wire so it can’t turn itself out. Lots of vibration going on
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Old 18-07-2018, 12:59   #11
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Re: Prop shaft involuntary decoupling from engine

Quote:
Originally Posted by Squanderbucks View Post
After putting shaft fully back in the coupler the first thing I would do is check the engine alignment. If it is out of line and vibrating too much doesn't matter how you fasten the shaft and set screw. It will lead to the failure of something else in the system - shaft, cutlass bearing, prop, or transmission.
I think this is a good point, although most engines vibrate enough to cause set screws to come out if they aren to wired.

I personally would wire it. There is no way it's coming out if it can't turn, and I trust wire over Loctite.

I'm also not a big fan of split couplers. Ideally the coupler is mated to the shaft and then the face is machined so it's perfectly perpendicular. Solid couplers lead to far fewer alignment problems, and are certainly the way to go for any shaft over 1".
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Old 18-07-2018, 13:07   #12
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Re: Prop shaft involuntary decoupling from engine

I just went through this myself. The set screws prevent the shaft from pulling out of the coupling (in reverse) and from sliding forward (in forward). The screws likely loosened due to vibration. Vibration can be caused by engine misalignment, a worn coupler, a worn cutlass bearing, a bent shaft, a bent strut or a loose strut. Here’s what I did when my set screws backed out of the coupler:

1. Realigned coupler and dimples on shaft and installed set screws.

2. Checked coupler alignment with transmission output flange, coupler face was badly rounded out.

3. Replaced coupler with new split coupler, not easy to press on with boat in water, had to run engine in forward to drive shaft into coupler.

4. Drilled new dimple (split coupler set screw is in different location from press on coupler).

5. Installed and wired set screw. There is a right way and many wrong ways to do this.

6. Checked alignment, coupler was true but engine was out of alignment, aligned engine.

7. Loud vibration under boat, hauled and replaced badly worn cutlass bearing. Strut OK. All well now.

My theory is that engine misalignment and rusty old coupler caused vibration that prematurely wore the cutlass (only 300 hours on it) and the whole shaking mess rattled out the set screws. My shaft actually backed out of the coupler a quarter inch or so. oonce a shaft starts moving in a press in coupler, the coupler is probably worn beyond reuse.
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