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Old 21-05-2013, 11:49   #1
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Driveshaft Coming out of Coupling

A newbie friend with an Alberg 30, repowered with a Yanmar 3GM30F.
Driveshaft has worked its way out of the coupling twice, in forward gear. Has an intermittent vibration issue which I suspect is the underlying problem. I am not nearby so hard to give much info. The coupling is a split coupling, 3 blade prop.
I suspect a either malalignment, a bent shaft or prop causing vibration leading to the shaft working loose. Access is poor at best of course.

Any ideas about troubleshooting or other causes?
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Old 21-05-2013, 12:03   #2
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Re: driveshaft coming out of coupling

propellor bent, shaft bent, cutlass bearing very worn.... all possible scenarios. I usually put a spit collar zinc on the inside about 1/2" from the coupling to avoid a significant problem.... but he does need to find out why. It is probably backing out when in reverse. Is it possible the split coupling was for a metric shaft and the shaft is a close size inch type? or vice versa? I prefer a keyed and lock bolted (or pinned) coupling
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Old 21-05-2013, 13:02   #3
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Re: driveshaft coming out of coupling

Was the shaft ever properly fit to the coupling or the prop? You shouldn't simply buy a prop, shaft and coupling and put them together. You should bring them to a machine shop and have them fit and faced. They will also drill in the dimple for the set screw.

Is there even a set screw?

You mentioned a bent shaft, was that checked by a machine shop for straightness? Even new shafts can have issues.

If its a split coupling, is he using a torque wrench to ensure that he has equal torque on both sides?

Was the engine and shaft properly aligned to the boat? If so, when? You typically can't do this alignment on the hard or even shortly after splashing due to the deflection in the hull from sitting on the keel.
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Old 21-05-2013, 13:59   #4
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Re: driveshaft coming out of coupling

Cutlass is good.
Shaft clearly came out in forward, do not know details of install, may have been substandard. Cannot easily check shaft without hauling. He is now trying locktite. Access makes a torque wrench quite challenging, may not be getting them tight enough due to access as well.
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Old 21-05-2013, 17:19   #5
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Re: driveshaft coming out of coupling

Your friend needs to be aware that once the shaft has slipped out of the coupling during operation, the coupling and shaft may have been damaged and the ability to clamp compromised.
If possible disassemble and inspect.

Regards,
Richard.
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Old 21-05-2013, 17:36   #6
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Re: driveshaft coming out of coupling

Shaft clearly came out in forward
Wierd... it must be really not fit well.... in forward the shaft should be trying to push into the engine .........right?
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Old 21-05-2013, 20:03   #7
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Re: Driveshaft Coming out of Coupling

anyone in Pensacola/Panama City area want to take a look at it for him?
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Old 21-05-2013, 22:57   #8
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Re: Driveshaft Coming out of Coupling

Has he checked the alignment between the engine couple and the shaft couple ?

Is this a V drive or not ?

Does he have collars on the shaft ? (Doesn't sound like it )

Can he separate the two couples and then put the engine in gear to make sure there is no engine problem ?

Are the engine feet in good shape ?

Need more info before we can help !
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Old 21-05-2013, 23:53   #9
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Re: Driveshaft Coming out of Coupling

If there's a P bracket or A bracket, another possible source of the symptom you describe would be a bent or misaligned bracket.
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Old 22-05-2013, 04:02   #10
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Re: Driveshaft Coming out of Coupling

I don't know what those brackets are?
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Old 22-05-2013, 04:49   #11
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Re: Driveshaft Coming out of Coupling

Think of a P bracket as like the casing of a saildrive:

it's attached to the hull to provide a bearing out by the prop, for hulls without a traditional keel or skeg for the sterntube to emerge from, and provide support to the shaft close to the prop.

An A bracket is like a P bracket except with two legs (so it looks like an upside down "A" from aft, whereas a P bracket looks like .... well, you get the idea....)

Fairly unusual to bend an A bracket, for obvious reasons.
[ Plumbers here talk about "P traps" from toilet bowls. It's a similar, geometrically descriptive term.

When (much) younger, I used to think it must be for trapping pee.... ]
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Old 22-05-2013, 07:10   #12
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Re: Driveshaft Coming out of Coupling

Thanks, never heard that term for them.
Boat is full keel, prop in aperture, no brackets, A, P, pee or otherwise.
I would think a bent shaft is therefor unlikely, but may have been a used shaft when installed.
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Old 22-05-2013, 08:10   #13
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Re: Driveshaft Coming out of Coupling

Andrew,

What you're calling a "P" bracket, in the States is usually called simply a strut, and it has a "cutlass" bearing in it. Another instance of being separated by a common language. ;-)

Ann

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