Coupler Failure

I had my coupler replace on my 95' 250 at 500 hours... the boat was only 2 years old then. It stripped because fishing line wrapped around my prop. I had an extended warentee, which was great because the job would have cost over $2K. The engine was pulled. Miss alignment would cause a premature failure. i would go back to the machanic and ask him how he can help you make it right...
 
aneely said:
I'm 99% sure. Once I remove the prop and double check the hub I'll remove any doubt but the way I was able to limp home yesterday has be pretty confident it's the coupler again. There is no cone clutch in the Alpha to my knowledge but I'm a newbie as I've only had this boat a little over 4 months
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i have not had a coupler go bad but i have had a couple spun prop hubs....the fact that you were able to 'limp home' has me leaning towards a spun prop hub....i would think that when a coupler goes bad it is usually a 'no go' situation...i would think the splines on the drive shaft and/or the teeth in the coupler are either stripped or not, nothing in between....a spun prop hub can have enough grab at low engine rpm's to move the boat at slow speed....

cliff
 
CliffA said:
i have not had a coupler go bad but i have had a couple spun prop hubs....the fact that you were able to 'limp home' has me leaning towards a spun prop hub....i would think that when a coupler goes bad it is usually a 'no go' situation...i would think the splines on the drive shaft and/or the teeth in the coupler are either stripped or not, nothing in between....a spun prop hub can have enough grab at low engine rpm's to move the boat at slow speed....

cliff
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Agreed... I've had one coupler go bad... it was no go. I would put it in gear and you would hear the rrzzzZZZ sound.
 
CliffA said:
i have not had a coupler go bad but i have had a couple spun prop hubs....the fact that you were able to 'limp home' has me leaning towards a spun prop hub....i would think that when a coupler goes bad it is usually a 'no go' situation...i would think the splines on the drive shaft and/or the teeth in the coupler are either stripped or not, nothing in between....a spun prop hub can have enough grab at low engine rpm's to move the boat at slow speed....

cliff
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Exactly what happened to me, I could limp home, but not above idle.

Molson9, sounds like you've worked on boats before so I would ask you to continue to contribute here. Very few of us are experts at this, so the voice of experience is MORE THAN WELCOMED!!! If your comments and/or suggestions are not relevant to the individual situation, the Original Poster can question you further or rule them out. Better to have several minds reviewing a problem than trying to figure them out on our own!
 
So I took the prop in today to get checked out and all is fine with the prop. Hub looks good.

Going to pull the drive off this Saturday to check the yolk shaft on the drive, per BillK, but the guy at the shop who checked the prop assured me that if the shaft were bad I would not have been able to limp in at all.

Hopefully with the drive pulled I'll be able to get more insight on weather or not I actually have another coupler failure and what caused it.

The guy mentioned something about cavitation creating the same scenerio as a failed coupler. Anyone have experience with repeated cavitation? Could having the wrong prop (pitch, etc) create cavitation?
 
aneely said:
So I took the prop in today to get checked out and all is fine with the prop. Hub looks good.

Going to pull the drive off this Saturday to check the yolk shaft on the drive, per BillK, but the guy at the shop who checked the prop assured me that if the shaft were bad I would not have been able to limp in at all.

Hopefully with the drive pulled I'll be able to get more insight on weather or not I actually have another coupler failure and what caused it.

The guy mentioned something about cavitation creating the same scenerio as a failed coupler. Anyone have experience with repeated cavitation? Could having the wrong prop (pitch, etc) create cavitation?
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I assume you have a Stainless Steal prop, since you stripped you coupler. I spun a hub on an Alpha drive, and I could not easily tell that the hub failed. I had a Mirage SS prop, and I replaced the hub in had the boat runing in about an hour. When I stripped my coupler the boat would not move at all. It was like the boat was in neutral. I don't see how you were able to limp home with a stripped coupler. Yes a wrong pitch prop can cause cavitation. Did you recently change your Prop?.../
 
I just purchased the boat back in Sept last year so I'm running the prop the previous owners had on the boat. I do not have a stainless steal prop, it's a 4 blade 14.5 D 18P and the hub is plastic so it's fairly easy to see if the hub has broken or not. I am positive the hub is fine...totally locks into place in the prop sung as a bug in a rug. The prop does have a lot of speckling on it, told this was signs of cavitation, so I'm thinking of just buying another prop to see if that solves my problem but as I'm fairly inexperienced as a boat owner I'd really like advice before shelling out the dough for a new prop.
 
Forgot to add regarding limping home with failed coupler. My understanding is that couplers can fail in two different ways. The metal can sheer where the spline from the drive contacts the coupler, where you are correct I would not have been able to limp home. Or the rubber can heat up and break its bond with the outer shell of the coupler that attaches to the flywheel, in which case there would still be rotation at the prop to limp home.
 
The hub of a coupler is rubber. It can fail just like the old-style hub of propellers in that it can be "spun". In that case, there would be no grinding or 'rrzzzZZZ sound' :smt001. Although that metal-sound is, indeed, another way that it can fail. The symptom of a spun coupler hub would feel a lot like a spun propeller hub in that you would typically have low speed power and possibly some moderate power - maybe even the ability to slowly get on plane.

There were a few (GOOD) points made above regarding figuring out WHY the first one spun. It could have been simply old age, but could be many of the things mentioned above, too.
 
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Don't get discouraged by others Molson. I appreciate you input and may in the end wind up doing this myself but for now I'm planning on asking the guy how replaced the coupler last month to make things right unless I can identify another reason for the increased rpm with lack of power to plane. Cavitation is one thing that was mentioned to me when I had the prop hub checked out. Do you have any experience with cavitation simulating a spun coupler or prop?
 
early in my boating life the first time i trimmed my outdrive up too far (due to inexperience) and the prop cavitated i thought i had spun the prop hub or coupler...so i idled back to the dock and loaded the boat on the trailer and took her home...i spent hours going through everything and could not find an obvious answer to why the prop lost bite with the water....decided to take the boat out again and play with the trim...i was able to recreate the situation by trimming the outdrive too high...as soon as i slowed down and lowered the outdrive the problem went away....another one of those 'learning experiences'......

so to answer your question, yes a cavitating prop can simulate a spun prop hub or spun coupler....

cliff
 
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"Technically" :smt001 speaking, trimming the drive up too high can induce ventilation, not cavitation. However the explanation (cause/effect) that Cliff gives is correct.

Cavitation is caused by small bubbles being created by the spinning prop - it will be much more noticeable if the prop blades are not true or if they have rough edges. Too much cavitation can cause the same general symptoms as ventilation. If the cavitation is severe enough, the bubbles (which can pop - almost like small explosions -- well, actually 'implosions') can actually eat away at the edges/blades of the propeller. It can cause something that resembles pock marks.

There's more science behind this than I can explain, but that's the jist of it.
 
Lazy Daze said:
"Technically" :smt001 speaking, trimming the drive up too high can induce ventilation, not cavitation. However the explanation (cause/effect) that Cliff gives is correct.

Cavitation is caused by small bubbles being created by the spinning prop - it will be much more noticeable if the prop blades are not true or if they have rough edges. Too much cavitation can cause the same general symptoms as ventilation. If the cavitation is severe enough, the bubbles (which can pop - almost like small explosions -- well, actually 'implosions') can actually eat away at the edges/blades of the propeller. It can cause something that resembles pock marks.

There's more science behind this than I can explain, but that's the jist of it.
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thanks for the correction Dennis....

cliff
 
Lazy Daze said:
The hub of a coupler is rubber. It can fail just like the old-style hub of propellers in that it can be "spun". In that case, there would be no grinding or 'rrzzzZZZ sound' :smt001. Although that metal-sound is, indeed, another way that it can fail. The symptom of a spun coupler hub would feel a lot like a spun propeller hub in that you would typically have low speed power and possibly some moderate power - maybe even the ability to slowly get on plane.

There were a few (GOOD) points made above regarding figuring out WHY the first one spun. It could have been simply old age, but could be many of the things mentioned above, too.
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+1. Thanks again Dennis (and some others) for a great post.
A.) I lost the coupler a few years ago & was able to limp back to my slip. Luckily less than a mile.
B.) Finding the why is by far the most important task. Unless you want to do it a third time.
 
Heard back from the mechanic who did the job last month and thankfully he said he will make things right. Turns out it was someone on his staff, who he has since fired, who did the work. I'm stressing that the why is very important to me, so much so that I'll take vacation time from work to be there in order to look at the mounts, drive shaft, etc. Hopefully this will be the end of the story. Stay tuned for the after and thanks for all the knowledge shared
 
If you have a few tools you could pull the alpha drive yourself and borrow an alignment tool before it goes back to the shop. If the drive pulls off easily the alignment is probably close. If you have to "pry" it off the engine is most likely misaligned. You will need to put the shifter in gear (I can't remember which way forward/reverse) to get the linkage aligned to pull the alpha. It is a two person job if you have never done it…..They are top heavy and hard to handle.



It would be easier to be at the shop and let the mechanic do this……….I would want to see myself now that you know there are issues and possible more "charges pending".
 
aneely said:
I'm stressing that the why is very important to me, so much so that I'll take vacation time from work to be there in order to look at the mounts, drive shaft, etc. Hopefully this will be the end of the story.
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since two couplers have failed i would take a very close look at the splines of the driveshaft...this could be the common link as the root cause for the failures....

cliff
 
I will Cliff but I would have thought if the splines were the cause of the failure there would have been a noise associated with the slipping problem. In my case it was all normal sounding just slippage which I interpreted as a failed bond between the rubber and metal portions of the coupler itself. But I will be sure to inspect the yolk and splines once the drive is pulled.

Andy
 
aneely said:
I will Cliff but I would have thought if the splines were the cause of the failure there would have been a noise associated with the slipping problem. In my case it was all normal sounding just slippage which I interpreted as a failed bond between the rubber and metal portions of the coupler itself. But I will be sure to inspect the yolk and splines once the drive is pulled.

Andy
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agreed Andy that you should have heard a very disturbing sound come from the coupler if the driveshaft splines were stripping the teeth in the coupler....since you did not hear this god awful noise maybe you just spun the rubber in the coupler....that would certainly be a less expensive situation to correct since the driveshaft should still be OK...

is it possible that the pitch on your prop is to high?....if you have too high of prop pitch and you try to accelerate hard from a dead stop it could be the engine is overpowering the coupler hub in its effort to move the boat quickly making the coupler hub break loose....

when things are running well can your engine reach its proper WOT range?.....if not the prop pitch may be too high as one possible reason....

cliff
 
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