Prop hub slip? '95 Maxum 4.3 L Mercruiser Alpha 1 Gen 2

sjm32157

Seaman
Joined
Jul 29, 2009
Messages
55
Boat has been running strong this year. In the water yesterday for about an hour, stopped to troll for a while. When powering back up to get on plane it goes nowhere. I reduced power to idle and tried again, moved slowly. Tried again after 30 seconds or so and gently got it back up on plane. Ran fine for remainder of the trip, about an hour. My prop is 9 years old, Solas, no issues until now. No burning rubber odor or residue in the engine bay that a failed coupler might give. I ordered a new prop. From other posts on the forum, if a coupler fails you are going nowhere and will overheat the engine since the pump impeller isn't spinning. I'm tempted to pull the outdrive and check the coupler splines to be sure. I haven't checked alignment for a couple of years so it's time for that too. Fingers crossed it spun a prop hub. Would debris in the water cause this to happen? Many many years ago I had a 120 Merc I/O. Coming back to the dock on a beautiful evening and the drive kicks into the air and boat comes to a stop. There was a 6 foot Christmas tree lodged between the drive and bell housing. I had to jump into the water and pry it out. Didn't see that one coming.....
 

alldodge

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Mar 8, 2009
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If something was caught on the prop it could do similar. Guessing you did check the prop after getting back.

There would be burnt rubber smell if you spun the coupler, and is always a good thing to check alignment. If it was the coupler you would start to over heat. Mark your prop and take it for a short run
 

GA_Boater

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My prop hub spun last year and nothing was hit. It was out of the blue with no warning and the first, hopefully last, time to spin a hub. 8 miles back to the ramp barely above idle took a long time.

I could spin the prop on the hub by hand, it was so loose. AllDodge said; mark the hub and check it.
 

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sjm32157

Seaman
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Jul 29, 2009
Messages
55
Tilted up the lower unit not long after the problem and also checked everything when we got home. Prop hardware is tight and no sign of any prop strike. Prop doesn't spin on the hub, acts normal. I read some other posts on the forum of other boaters having similar experiences and results with propellers. I don't think a bad coupler would "heal itself". I won't go back to the river without the new prop installed.
 

alldodge

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Suggest pulling the drive and check the coupler. If the drive is out of alignment for long enough the drive shaft will eat up the inner coupling. Given enough time it will eat away all the teeth and start slipping. If this happens you will not smell any rubber burning. Note in pic below this coupler has not given way (note points on teeth) but would very soon.

bad-coupler.jpg

New coupler

images.jpg
 

sjm32157

Seaman
Joined
Jul 29, 2009
Messages
55
I think I will definitely pull the drive and have a look. Boat was refreshed about 100 hrs ago with a Jasper long block but I think the shop used the original coupler.
 

sjm32157

Seaman
Joined
Jul 29, 2009
Messages
55
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I pulled the drive off of the boat tonight and after I removed a ton of blue grease, I had a chance to inspect the coupler splines. The splines look to be in good condition and still square. I inserted my alignment bar and it bottomed against the engine. Required 3 or 4 fingers of pull to insert and remove so I may play around with the mounts to free it up a bit. My alignment tool is machinist made, not an official Mercruiser tool. I hope the new prop cures my problem.
 

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