Bad engine coupler or spun prop hub?

[Nede2]

5.0L Mercruiser 2006 Alpha gen 2 drive.
Recently replaced IAC.

Boat had broken bow line at a dock and was blown into the dock repeatedly with the drive hitting the dock. Did the drive get knocked out of alignment? We were able to get home fine after that incident. It was about 30 minutes down river.

We set out today to the beach and as I began to give the boat throttle it responded up to a certain point and then it seemed like the propulsion stopped but the engine kept revving and reved higher when the propulsion stopped. 2 things I’m thinking of: bad engine coupler or the hub in the prop is spun. I think I am going to borrow a prop from a friend and see if the boat responds the same way. We were able to get back to the dock under power and propulsion. Under low load it putted around fine, it was only when I gave it some load that it dropped out.

One person was of the mind that if the engine coupler failed that there would be no transmission to the drive.

Any trouble shooting ideas would be appreciated.

 

[Scott Danforth]

simply draw a line with a sharpie across the prop and prop nut. if the line moves, its the prop

yes, if the coupler fails, there is no propulsion

 

[tank1949]

5.0L Mercruiser 2006 Alpha gen 2 drive.
Recently replaced IAC.

Boat had broken bow line at a dock and was blown into the dock repeatedly with the drive hitting the dock. Did the drive get knocked out of alignment? We were able to get home fine after that incident. It was about 30 minutes down river.

We set out today to the beach and as I began to give the boat throttle it responded up to a certain point and then it seemed like the propulsion stopped but the engine kept revving and reved higher when the propulsion stopped. 2 things I’m thinking of: bad engine coupler or the hub in the prop is spun. I think I am going to borrow a prop from a friend and see if the boat responds the same way. We were able to get back to the dock under power and propulsion. Under low load it putted around fine, it was only when I gave it some load that it dropped out.

One person was of the mind that if the engine coupler failed that there would be no transmission to the drive.

Any trouble shooting ideas would be appreciated.

I suspect only prop hub is damaged and slipping. Take it to a shop for examination. If you can lockup motor so motor will not spin, you can remove prop and install a couple of jam nuts on prop shaft and use a huge breaker bar to see if shaft moves. If it does, chances are that your coupler is defective.

 

[ScottinAZ]

pull the prop nut and outer washers. if there is signs of "fresh" metal there and on the thrust washer, the prop has been spinning independent of the hub..... just went through this earlier this season with your exact symptoms.... changed prop, problem solved.

start simple and cheap. the prop is a MUCH cheaper option than the coupler hub. if a buddy has one that will fit, it will tell the tale.... if it works, its the prop, if it still slips, its the coupler.

 

[salty3rd]

You can rule out the coupler if you look at the back of the engine and see if the input shaft is spinning when the engine is running.

 

[QBhoy]

Be the hub I’d think. Any coupler failing that I’ve been about or close to…you know all about it from the smell of it alone.

 

[Nede2]

Got a call from the shop. Inspected the prop. They pulled the drive and inspected it. Inspected the coupler and saw nothing wrong. Put it back together and took it out to the channel **** pounded it planing multiple times. I don’t understand. There was definitely a problem.

 

[nola mike]

Got a call from the shop. Inspected the prop. They pulled the drive and inspected it. Inspected the coupler and saw nothing wrong. Put it back together and took it out to the channel **** pounded it planing multiple times. I don’t understand. There was definitely a problem.

I've had weeds wrapped around the prop that made it behave similarly. Shouldn't, but did.

 

[QBhoy]

If they didn’t change the prop hub…it could be just hanging on, then suddenly let you down again.

 

[Nede2]

Got it back from the shop. Put it in the water and had the exact same problem. I had my mechanic and boat guy buddy look at the prop. It has the flo-torq 2 hub kit. He said that there’s no way that style hub can spin and he thinks it’s the coupler. When the shop tested it they had one maybe 2 guys in it. When we use it, it has 5 people plus gear. Their test was not apples to apples.

 

[dubs283]

Did any if these fellas pull the prop, disassemble the hub and inspect?

Flo torq hub is readily available through mercury alone, not part of a kit. Cheap, easy test

If you can survive a week without your boat it's okay to relinquish your prop to a reputable shop for inspection/rebuild. Stainless ought to be less then $10,000 for the process

 

[QBhoy]

Got it back from the shop. Put it in the water and had the exact same problem. I had my mechanic and boat guy buddy look at the prop. It has the flo-torq 2 hub kit. He said that there’s no way that style hub can spin and he thinks it’s the coupler. When the shop tested it they had one maybe 2 guys in it. When we use it, it has 5 people plus gear. Their test was not apples to apples.

That hub can definitely spin…it’s absolutely and inherently designed to do just that, in a sacrificial act, to protect the gearbox. Shocking statement from your mechanic/shop there. Knock the hub insert out the prop for a proper look to make sure. May not be to blame perhaps…but if anyone has literally told you it’s impossible for that particular hub kit to give way and spin…that’s simply absurd and not true. Have a closer look at the assembly and integrity of the hub after it’s removed I’d suggest. It’s not always apparently obvious at a glance. They usually crack, when they give way and sacrifice. Which means that when under load, they hold firm enough together at minimum load/idle speed or just over…but further stress or rpm load, they give way and slip. To the glancing eye when prop removed and looking in…a hairline crack is often not too readily obviously found or blatant. It will naturally return to its shape or form without the torque of a turning shaft opening it up

 

[Nede2]

The coupler was removed and it appears that it was bad.

 

[Nede2]

Replaced coupler put it back together. Took it out for a test run and the first attempt to plane failed. It spun out and overreved. I tried about 7-8 more times and it hooked up each of those times.

 

[ROY WILLIAMS]

Replaced coupler put it back together. Took it out for a test run and the first attempt to plane failed. It spun out and overreved. I tried about 7-8 more times and it hooked up each of those times.

the prop coupler is the company spec part # ?
the prop is the company ? and the prop spec ?

 

[Nede2]

Replaced coupler put it back together. Took it out for a

the prop coupler is the company spec part # ?
the prop is the company ? and

Coupler is a Sierra cross 18-2323. No OEM available that I could find.
Prop is Mercury black max 3 blade 14.25” 21 pitch 48-832832A45

 

[ROY WILLIAMS]

Replaced coupler put it back together. Took it out for a

Coupler is a Sierra cross 18-2323. No OEM available that I could find.
Prop is Mercury black max 3 blade 14.25” 21 pitch 48-832832A45

the engine coupler is worn ..

 

[Nede2]

Are you saying the new sierra coupler is worn right out of the box?

 

[flashback]

Swap out the prop with a known good one to eliminate that possible cause...

 

[ScottinAZ]

Swap out the prop with a known good one to eliminate that possible cause...

being honest, I woulda done that before ponying up for a coupler swap......