Bad Coupler

[Dave87]

Thank you everyone for helping me find the issue.

As I removed the engine all the motor mounts seem to be fine.

I did notice the back left mounting screw was not as snug as the other three.

I recently changed the pitch on my prop from 21 to 23.

Would this have caused my coupler to wear out ?

Or is it simply due to old age ?

The boat is a 1991 so and it has 600 hours on it.

Thanks for the help

 

[Bondo]

Would this have caused my coupler to wear out ?

Ayuh,..... A lack of grease is a big coupler killer,.....

 

[tank1949]

Thank you everyone for helping me find the issue.

As I removed the engine all the motor mounts seem to be fine.

I did notice the back left mounting screw was not as snug as the other three.

I recently changed the pitch on my prop from 21 to 23.

Would this have caused my coupler to wear out ?

Or is it simply due to old age ?

The boat is a 1991 so and it has 600 hours on it.

Thanks for the help

No grease and/or saggy alignment due to lose mount nuts or ROT.

 

[Dave87]

I'm sorry this might sound naive but how could a lack of grease cause this to wear ?

 

[Bt Doctur]

Absolutely post a pic of the rear mounts sometimes a collapsed mount is visible to the eye

 

[achris]

I'm sorry this might sound naive but how could a lack of grease cause this to wear ?

The input shaft splines are steel. The coupler splines are aluminium... And rubber based rear and side engine mounts will allow a tiny bit of movement between the shaft and the coupler. No grease (or not enough grease) and you get a fantastically quick destruction of the aluminium... Just like in your photo.

Chris........

 

[Scott Danforth]

and that movement is every time a piston fires. only takes a short bit of time to wipe out the splines

 

[GA_Boater]

It also the driveshaft moves in and out while trimming, also up and down and sideways for every rotation with only a single universal joint driveshaft.

Coupled with what Chris and Scott said, the prop load varies as the prop approaches or comes out of the water surface.

Couplers take a heck of a beating.

 

[achris]

And low speed is even worse! as the boat surges it unloads the prop, effectively allowing the coupler splines to unload, so you get a load/unload scenario... Just like in a car with that clunk, clunk from the diff...

Yeah, couplers take a beating!

Chris.......

 

[muc]

Yes, lack of lube, bad alignment and a lot of time at idle especially with a 454 kills them.
Your new coupler should come with grease fittings.

MerCruiser sells a steel coupler for heavy duty applications. It costs extra.

 

[achris]

...MerCruiser sells a steel coupler for heavy duty applications. It costs extra.

Gee, there's a surprise....

Chris.....

 

[Dave87]

Absolutely post a pic of the rear mounts sometimes a collapsed mount is visible to the eye

Here are the rear mounts. Let me know what you think..

 

[muc]

Here are the rear mounts. Let me know what you think..

The rubber mounts are in the flywheel cover that’s on the engine.

 

[scoflaw]

The rubber mounts are in the flywheel cover that’s on the engine.

So what collapses ? Isn't the steel bushing in the center of the rubber doing the heavy lifting ?

 

[Rick Stephens]

So what collapses ? Isn't the steel bushing in the center of the rubber doing the heavy lifting ?

Just like the coupler, the vulcanized rubber connection to the steel bushing is where the failure occurs.

 

[Dave87]

Looks like everything is ok here to me. What do you all think ? kinda even looks new to me....

Thanks once again!

 

[achris]

Photos of engine mounts from above are no good. We need to see them in profile so we can see if there's any sag....

 

[Bt Doctur]

when a rear mount fails the engine squats down and removes the coupler

 

[Dave87]

Photos of engine mounts from above are no good. We need to see them in profile so we can see if there's any sag....

My bad I'm new at this.

Here you go.

 

[achris]

Getting closer, and from here they look ok... Could you get a shot like this.... And looking 'up' at the mount slightly..? please...