Lots of experience here so figure I’ll ask - outboard Mercury engine vibration

[jlcj7]

Lots of people here have had many different kinds of boats (including me. But I am most familiar with Yamaha jet skis and boats). So worth a shot for ideas.
I have a Harris pontoon with a 200 Mercury outboard (2020). Today when cruising along it all of a sudden started what felt like cavitation. I figured I caught some fishing line or something. Trimmed the motor up, nothing obvious. So, when back to my dock and put the boat in the air to get a better look. Didn’t see anything so pulled the prop off, checked gear oil. All ok and no obvious wear or signs of damage.
Any other thoughts? Was thinking it was prop related but what do I know. I more i accelerated the worse the vibration got. Next steps I will change fuel filter and spark plugs to to be sure it that.
Anything else i am missing? Any thought or help is appreciated. Very new to outboards.

 

[diehard]

maybe the hub spun in the prop put a mark on hub and prop test run and see if the marks are in same place,

 

[jlcj7]

will give this a try. Thanks.

 

[Bilmon]

Just a shot in the dark but my 2017 75 hp has a plastic [ nylon?] bushing behind the prop to block exhaust from leaking behind the prop. It is easy to damage and I have had one come lose and spin with the prop causing it to vibrate . As I understand it, it can also cause cavitation by leaking exhaust over the prop instead of though the prop. Cheap and easy to replace so I carry a spare. Worth a quick look.

 

[Bilmon]

Just took a quick look at my spare one while I was hooking up my jet for a day on the Mississippi. It's called a prop bore sleeve

 

[jlcj7]

I don’t think I have a nylon bushing.
have a metal spacer and another sleeve thing. Everything looks normal.

 

[Weeb]

Was there any space between the locknut and the propeller? It wouldn’t take much to make it wobble

 

[jlcj7]

No. Tight. I even pulled it off checked gear oil and reassembled and torqued to correct spec.
Long shot but going to change spark plugs and fuel filter just in case it is a gas/misfire issue

 

[Sbrown]

I would look really close at the splined interface where the drive sleeve and the drive sleeve adapter interface. Those are parts b and d on the schematic. That interface is what transfers torque from the prop shaft to the prop and is designed to slip if the prop contacts anything. Once it slips, the drive sleeve needs to be replaced. Should be pretty obvious when you look at it close.

 

[jlcj7]

I think you may be on to something. Does this look slightly damaged to you? Can’t tell if it looks like it spun or if those are notches the nylon sleeve slides in on.

 

[Neutron]

Looks ok from the picture but i would remove it anyway and inspect. It pops out towards the rear of the prop. If you have one available then replace it and reassemble

 

[Sbrown]

I think you may be on to something. Does this look slightly damaged to you? Can’t tell if it looks like it spun or if those are notches the nylon sleeve slides in on.
View attachment 181218View attachment 181219View attachment 181220

Ok, tough to tell, but I think you have a prop with an integrated hub there, if that is true, it definitely looks to me like its been slipping.

 

[jlcj7]

Yes. I have watched a bunch of videos on removing that sleeve and mine is different. There is a metal insert inside the plastic.

back side.



front side.

 

[jlcj7]

We’ll update: took the prop the someone who knows more than me, they didn’t think anything was wrong with it.

just as a last effort I had ordered spark plugs and fuel filter which arrived so I changed them. Boat runs great again?!?!

seems odd. Boat has 37 hours and I ran it already this season with no issues. So not convinced I solved the problem but maybe a plug fouled or something.

 

[Sbrown]

We’ll update: took the prop the someone who knows more than me, they didn’t think anything was wrong with it.

just as a last effort I had ordered spark plugs and fuel filter which arrived so I changed them. Boat runs great again?!?!

seems odd. Boat has 37 hours and I ran it already this season with no issues. So not convinced I solved the problem but maybe a plug fouled or something.

Glad you found the issue and it was something simple to repair.