The signs of a bad coupler ?

[mwph]

From what I have read over the last couple of years, I fear that I'll need to rplace the coupler. Here is a brief summary of what happened.

Two weeks ago the boat performed flawlessly, including two nice little runs on plane with the admiral at the helm. (finnaly!:smt038)

Today we idle out through the no wake zone on extremely flat water. Once out, I slowly increased throttle but got minimal response. At about 1400 rpm it felt like the boat was trying to pull a loaded barge.

My first thought was a tangled mess of weeds, or worse, around the B3 props, that I could not shake loose. So I idled back into my slip & got into the water to take a look. I found clean & smooth (undamaged) props.

For what its worth the drive, and all fluid levels are fine. Ran the engine throttle only up around 2k a time or two & it sounded fine. In retrospect, the only other point I can add is that when I was idling out the boat seemed to be wandering abnormally.

So... If I understand things correctly, the B3 uses no rubber hubs to be "spun". So next thought is the coupler. Am I correct? Does my problem sound like the coupler has taken a hike? Is the coupler considered a wear item? I ask this because of the previous outings performance & we certianly didn't "hit" anything. My fear is that an engine alignment check 6 months ago may have prevnted this. Am I on the right track with these questions?

If my questions & assumptions are way off, well, I can take a harsh verbal bashing. As long as I can learn from it. Thanks in advance.

 

[Dave S]

You didn't mention it, but if you have a burnt rubber smell in the engine compartment that is indicative of the coupler going bad.

Dave

 

[Chris Dauth]

From your description, it doesn't sound like the coupler.

Usually, once the coupler lets go, there is no halfway. There may still be a bit if friction left and if you take the engine up to normal cruising rpms, you will find the boat will just go slower, maybe not over about 8 knots. And you will smell burning rubber in the engine room. (as in the above post).

Seems to me the boats bottom needs a good clean off. I know that a dozen barnacles or so or a bit of weed growth will easily knock off 15 knots, especially if you have some on the props.

BTW, the coupler on the back of a 454 is a pretty tough unit. :thumbsup:

 

[fwebster]

OK....but he is located inland on a freshwater lake. The worst fouling he will have is a little slime on the bottom.

 

[Don Sr]

I had the same type issue. It turned out to be the gas. If no burnt rubber go through your fuel system and check replace filters, seperators etc.

 

[mwph]

1. Burnt rubber smell - I did not smell anything. The wife said "she thought" she might have. But I know that doesn' help much here.

2. Gowth - Slime yes, but as I posted, last week's run was flawless and the props are clean & damage free.

3. Fuel - I've hd the boat out 3 or 4 times since my last fueling, so I've run it from full to about 3/8 full. Also, as posted, I ran the engine, throttle only up to 2k or so with no signs of any problem.

Thanks for the replys so far

 

[Don Sr]

If was a spun coupler / prop the rpm would jump suddenly upward as the hub or shaft would break free as the load increased. Does the rpm increase smootly through 4000? Is there a hesitation ? How rpm compare to previous recorded speeds. How long does the boat sit between outings?

 

[Thomas Molin]

To me it sounds like it doesn´t get enough fuel when you increase throttle. Easy check no 1 is to open the gas fill cap to see if the fuel tank vent isn´t clogged so you get vacuum in the tank. For no 2, I would change the fuel filter. No 3, check that the gas pump works properly.

 

[320Bob]

MWPH,
I had to replace the coupler on an identically configured boat to yours when I traded it in on my Sea Ray. There were no noticiable signs of any problems before the Sea Ray dealer pulled the drive to do a trade check. I was told, normal indications of a worn coupler were "growling" noices coming from the engine compartment which I had none. The problem with that engine-drive combination was Mercruiser put an aluminum coupler on the engine and a steel spline shaft on the B3 drive. Aluminum is softer than steel. The replacement coupler they put on was made of steel and the cost was $1,500 because they had to pull the engine to replace the coupler. Hopefully, the suggestions of others are what the problem is and not the coupler.

 

[mwph]

If was a spun coupler / prop the rpm would jump suddenly upward as the hub or shaft would break free as the load increased. Does the rpm increase smootly through 4000? Is there a hesitation ? How rpm compare to previous recorded speeds. How long does the boat sit between outings?

I can not report a comparison of speeds/rpms to previous outings because both under load & running throttle only I only took the RPMs up near 2300. It did so smoothly. Is this high enough to rule out fuel issues?

The boat sat for 12 days between outings. Last time out the boat was on plane & running normally, including our final run to just before the no wake zone. From there we idled into our slip with no noticeable problems.

 

[Thomas Molin]

I can not report a comparison of speeds/rpms to previous outings because both under load & running throttle only I only took the RPMs up near 2300. It did so smoothly. Is this high enough to rule out fuel issues?

The boat sat for 12 days between outings. Last time out the boat was on plane & running normally, including our final run to just before the no wake zone. From there we idled into our slip with no noticeable problems.

In my opinion, you can have fuel issues anyway. When you try to reach 3000-3500 rpm, you will burn about the double amount of fuel compared to 2300 rpm. If that flow isn´t enough, the engine will stall. I still think the fix is as easy as open the gas filler cap to let some fresh air in to remove vacuum.

 

[Don Sr]

Sure sounds like a fuel issue. if no vacuum as described above replace the filters/water seperater and try run the boat under load through the rpm range. If still no power check the fuel pump.