Acting like a spun prop hub but it's not. What do I try next?

[Tmakaro]

I have a 2010 Bayliner 192 with a 4.3L Mercruiser and a Alpha 1 gen 2 leg. The other day when I was on the water, I couldn't get up on plane. The fastest I could go was 16mph revving at 2800 rpm. When I push the throttle down, the engine revs to 5000 rpm but the boat doesn't go any faster.
So I put on a new propeller with a new hub and sea test it. Same problem! After pulling off the propeller and inspecting the hub I can see it is perfectly fine and looks like new. The prop hub is not spun.
I drained the gear oil and found no metal shavings. I tried stepping on the propeller with the boat in gear and the engine turned over.

What do I do next? Pull the leg and check the engine coupler? Does the engine coupler have a plastic hub too? Can an engine coupler even fail partially like I am experiencing?

Could there be any other reason for this problem I am having? From my understanding, the power is a direct drive from the engine to the propeller, so if the engine revs at 4000rpm, that should get directly to the propeller.

 

[Scott06]

Check the engine coupler and drive

Coupler could be broken
Drive could have shredded upper gears or broken vertical driveshaft

Would be leaning towards coupler based on symptoms look for signs of burning rubber at rear of engine as coupler connects engine to drive input shaft

 

[Rick Stephens]

You can pull the outdrive and shine a flashlight through the gimbal bearing and reasonably well inspect the splines in the coupler and the rubber around the metal splines. My bet is the rubber will show as melted and the center spline section having spun inside the rubber.

 

[Tmakaro]

Thanks. I pulled the drive off and the splines look fine. I'm going to try and look at the rubber but it's hard to see

 

[Rick Stephens]

If you have an alignment bar - an essential tool before you reinstall a drive, then you can swivel the gimbal bearing a bit to point enough to the side to get a better look at the rubber.

 

[flashback]

I'm guessing you could smell a spun coupler.

 

[Rick Stephens]

I'm guessing you could smell a spun coupler.

Maybe

 

[flashback]

Maybe

Well I don't want to find outThat's for sure!

 

[alldodge]

If its not the prop hub, its the coupler
Nothing else is in the mix

 

[nola mike]

If its not the prop hub, its the coupler
Nothing else is in the mix

Or the drive. Pull the top cap and check out the gears.

 

[alldodge]

Or the drive. Pull the top cap and check out the gears.

No, and think about it
Has power to 2800 rpm, anything above that it looses all forward motion.

If drive is busted it won't move at all

 

[nola mike]

No, and think about it
Has power to 2800 rpm, anything above that it looses all forward motion.

If drive is busted it won't move at all

Most likely you're right, but hell who knows. Just threw that out as a "what else can kill propulsion". If a V8 can run with a busted crank, I can see a world where the gears are shredding and moving for a few seconds before smoothing out completely.

 

[QBhoy]

Got to be either the hub or the coupler. You’d smell the coupler for sure. No mistaking it. Stinks of burning rubber.

 

[QBhoy]

I have a 2010 Bayliner 192 with a 4.3L Mercruiser and a Alpha 1 gen 2 leg. The other day when I was on the water, I couldn't get up on plane. The fastest I could go was 16mph revving at 2800 rpm. When I push the throttle down, the engine revs to 5000 rpm but the boat doesn't go any faster.
So I put on a new propeller with a new hub and sea test it. Same problem! After pulling off the propeller and inspecting the hub I can see it is perfectly fine and looks like new. The prop hub is not spun.
I drained the gear oil and found no metal shavings. I tried stepping on the propeller with the boat in gear and the engine turned over.

What do I do next? Pull the leg and check the engine coupler? Does the engine coupler have a plastic hub too? Can an engine coupler even fail partially like I am experiencing?

Could there be any other reason for this problem I am having? From my understanding, the power is a direct drive from the engine to the propeller, so if the engine revs at 4000rpm, that should get directly to the propeller.

Did the engine definitely turn when you stepped on the prop ? That wouldn’t be too easy to accomplish usually. Any pics of the prop on the out drive?

 

[dubs283]

Did the engine definitely turn when you stepped on the prop ? That wouldn’t be too easy to accomplish usually.

This was my initial thought. Can't rule out a pooched motor at this point

OP: you need to pull the drive, inspect and get eyes on the coupler