Mercruiser alpha one gear slipping under torque

[David.c55]

hey, so I have a 1984 celebrity that has a 5.0 mercruiser alpha one. The last few times we've taken it on the water it has been slipping out of gear once it hits around 2,500 rpms. However the weird thing is when we first out it on the water, it will go to a plane, no problems. But when we stop, then start it up to move to another spot, right before it goes to plane the boat will stop and the rpms will shoot up like it went back into neutral. We then but the shifter in neutral and slowly climb back into a plane and it will slip again. It won't slip until it hits around 2500 rpms. We've gotten the shifter cables adjusted by a shop, we also gotten a rebuilt outdrive, and I had boughten an engine coupler incase that was the issue. There was no burning smell or any grinding sounds as if the coupler has gone. Also we tested the prop and it does not have a spun hub. Any ideas what could be causing this??

 

[thumpar]

How did you test for a spun prop hub?

 

[wahlejim]

If there aren't any strange noises, it sure sounds like the hub in the prop is going bad. Agree with thumpar, we need to know what process you used for testing the prop hub

 

[Fishermark]

^^^ Yep. You cannot tell if the prop is bad by looking at it. Nor even trying to twist it by hand. You can mark the hub and prop, then take the boat out and run it till something slips again. Then check the marks and see if they have moved. Or you can try a different prop. But I would be curious as to how you tested the prop.

Otherwise, you are down the coupler. Most any internal problem is going to not be intermittent.

 

[Bondo]

Ayuh,.... Welcome Aboard,..... With those symptoms, is pretty much Gotta be the prop, or the coupler,....

 

[David.c55]

I've only tried to spin the prop by hand when the drive is in gear, I was told that if the hub was bad the prop would move. When I get the chance to get the boat back together I'll try using the mark test on the back of the prop.