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Slipping engine coupler?

J

Jacob Welch

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I recently replaced the engine coupler on my 87 SeaRay it has a 4.3 with Alpha 1 outdrive. I believe that I got the motor aligned correctly. When I take it out it will run great for about 30 minutes then the coupler will start to slip. Is there anything else other than the motor alignment that could be causing the coupler to slip?

Thanks.
 
Are you sure it's the coupler slipping? A bad prop hub will do the same thing. Take the prop off, look at the hub for any roughness near the outside edge of the rubber (where it meets the prop metal), if it looks ripped, it probably is. Next take a permanent magic marker, and put a mark across the center of the prop, and the nut as well once you get it back on, to confirm. Any movement here means it's bad
 
Yes, I am sure that its the coupler. At first I thought it was the prop. After more investigation I found it was the coupler. The coupler that I replaced was destroyed! Since putting the new one on it will react great for awhile even under high RPM's but then it will start to slip. You can smell the rubber burning. I opened up the engine cover and you can see the flywheel turning and the output shaft is barely turning. I thought I got the motor aligned correctly when I put it back together. The output shaft spun freely and inserted easily when installing. I just wasn't sure if there could be any other reason that would cause the coupler to slip? I am by no means a boat mechanic so I appreciate any help!

Thanks,
 
So, then how much resistance is in your spline, driveshaft, and or drive gears? Is something binding badly in the drive? I'd take it off, and check it out! It had better turn like butter at the drive in gear.
 
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Is this a noname aftermarket coupler? A seizing drive shouldn't take out a brand new coupler behind a V6, but it could probably tear up a cheap one.
New coupler slipping after 30 minutes = I say you got a bad coupler.

A brutally misaligned coupler will live for a week and heck, I've seen them go three seasons with an engine wiggling around on rotten stringers.
 
Jacob Welch said:
I recently replaced the engine coupler on my 87 SeaRay it has a 4.3 with Alpha 1 outdrive. I believe that I got the motor aligned correctly. When I take it out it will run great for about 30 minutes then the coupler will start to slip. Is there anything else other than the motor alignment that could be causing the coupler to slip?

Thanks.
Click to expand...

Did you purchase a new one or install a used one?
 
I can't imagine a new coupler failing as noted above. I've only seen them fail under high hp conditions or just getting old, usually more than 15 yrs or so.
A 4.3 would really have a tough time tearing up a new coupler.
I still like the prop slippage possibility.
 
Villain lll said:
I can't imagine a new coupler failing as noted above. I've only seen them fail under high hp conditions or just getting old, usually more than 15 yrs or so.
A 4.3 would really have a tough time tearing up a new coupler.
I still like the prop slippage possibility.
Click to expand...


One other thing, the splines on the drive shaft are severly worn or shot..........that would slip for sure

Is the "new" coupler for mercruiser? Or is it for some other manufacturer and maybe the ID is too large???

missing some info.........
 
It had a 19pitch prop on it. I originally thought it was the prop so I bought a 23 pitch prop. Still had same issue. Done more investigating and found that the coupler was destroyed. Went to a nearby well recommended marine shop and ordered new coupler, output shaft, gimble bearing and bellows. Replaced all of it. I'm not sure what brand the coupler was. It cost me $360 for the coupler alone. I can take the boat out for about 30 minutes or so and it operates great. Then it will fall on its face but motor is still turning RPM. Then you can smell burnt rubber. I took the engine cover off while the boat was in gear and turning 2000RPM. You could see the flywheel turning at the correct RPM but the output shaft is barely turning and you can see smoke coming from the coupler. I'm pretty certain its the coupler I just don't know what all can cause a coupler to slip.

I've taken the lower unit off a couple times and it comes apart and goes together smoothly. Everything turns freely. I'm at a loss.
 
Here are a couple of pictures of the coupler I replaced.
 

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Check the engine mounts for rot and review engine/coupler alignment procedures. Verify you have the correct coupler.
 
If the motor is spinning and the input shaft is NOT the coupler has spun again.........

The question becomes WHY?
 
When you install this yet again new drive coupler, make dam sure that you go through the propper engine drive coupler alignment procedure.
If you don't get the alignment correct..... you will ruin another drive coupler!

Check the inner transom plate attachment......... and make certain that it is snug and has not slipped.
Make certain that the rear flywheel cover engine supports are correctly assembled.



.
 
MikDee said:
So, then how much resistance is in your spline, driveshaft, and or drive gears? Is something binding badly in the drive? I'd take it off, and check it out! It had better turn like butter at the drive in gear.
Click to expand...

Again, could there be something in the outdrive that is binding once you are in gear? Or maybe the prop is binding somehow? I know, I'm grabbing at straws here, because it doesn't sound logical, especially if you have the alignment done right.

I had this happen to me yrs ago on a straight six Mercruiser 165hp, right after I got done rebuilding the engine :( It is quite Frustrating, I should have replaced the coupling during the rebuild. I ended up selling the boat, at somewhat of a loss.

Do you think that maybe the back mounts of your engine are bad, causing it to wobble, & bind under load?
 
You stated he it originally had a 19" prop and you replaced it with 23' prop still ad the same problem.... Something had to change specifically the RPM performance.

Are you able to get to the correct Wide Open Throttle RPM (WOT)?

By making such a radical prop pitch change, WOT HAD to change, probably for the worse, similar WOT and extra heavy load issues would occur with incorrect outdrive gear ratios (4cyl,6cyl, V8 etc).

If the motor had the horsepower to do so, excessive coupling failure could occur if the drive ratio and prop specs are wrong.

Did your rig ever run correctly and was it able to attain 4400-4600 RPM at WOT?
 
The OP doesn't state the size of his boat nor is in his profile but to Kaysea's point, a 23 pitch prop on any 4.3 driven boat would be way too much prop. If 19 was stock, even a 21 pitch would be pushing it, trying max out rpm's, not to mention the time it would take to plane.
That coupler if correctly installed should not ever be an issue when new.
To the other's point of view, check alignment carefully and put back on the stock prop.
 
Villain lll said:
The OP doesn't state the size of his boat nor is in his profile but to Kaysea's point, a 23 pitch prop on any 4.3 driven boat would be way too much prop. If 19 was stock, even a 21 pitch would be pushing it, trying max out rpm's, not to mention the time it would take to plane.
That coupler if correctly installed should not ever be an issue when new.
To the other's point of view, check alignment carefully and put back on the stock prop.
Click to expand...

Sorry, I changed from a 19 to a 21 not a 23. Typo on my part. Yes I could achieve wot without issues for awhile. Obviously a change in speed. Once I determined it wasn't a bad prop I went back to the 19.
 
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