# Mercury rattle



## formerWAflyfisher

Ok so I had this motor serviced about 6-8 months ago because it was making this noise and it stopped for awhile.  Now its back.  The mechanic did a normal yearly service and charged me to fix a backing plate that was broken.  He said there is a plate between the prop and the housing that rattles and make a noise that sounds like a bell.   Something about the 2-300 dollars he charged for this item/installation and the way he described it didn't sit well.  Not looking to bash I just paid the man and will never go back.  Well the noise is back it sounds like the lower unit has a bell that rings at idle.  Any insight as to what is making this noise and how to stop it or just live with it.  




It's much louder in person than in the vid.  It's a 2010 mercury 40 four stroke, With a naturally polished and reshaped aluminum prop.:


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## HaMm3r

Let me ask the obvious...

Have you taken the prop off and run the motor, looking for said plate?


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## mark_gardner

I had a rattle but that was the recoil assembly about to fall off I cant imagine what in the lower unit could be rattling :-/


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## rc

You need to replace the thrust washer located between your prop and the lower unit housing.


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## Creek Runner

> You need to replace the thrust washer located between your prop and the lower unit housing.


Umm in 15+ years of working on outboards I have maybe seen 1 bad thrust washer. And surely if the mechanic that worked on it already put on a new thrust washer and its bad again, there is something else going on. 

Thrust washer was going to be my 1st guess to when all I did was watch the video, but when I went back and read the text he wrote; something doesn't make sense. Not sure what plate the mechanic replaced or is talking about unless inside the housing, which would align more with what was charged. But it wouldn't be describe as between the prop and housing. 

Hope it is the thrust washer they are about $10 bucks and takes about 2min to install. 

Good luck


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## DuckNut

John, to me it sounds like heavy metal on heavy metal.

It sounds like the gears are at the point of trying to engage and the teeth from one gear is bouncing on the top of the other gear.

Try moving your gear selector making sure it is centered in neutral. If that quiets it down make the necessary adjustments.

Sorry for my technical terms.


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## formerWAflyfisher

Thanks for the posts guys. I've been to busy to take the prop off and check. I will work on the motor this Saturday. Hopefully it is just the thrust washer.


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## formerWAflyfisher

Ducknut. It doesn't seem to matter if the motor is in gear R/N/F it makes the same noise at idle. The only thing that seems to quite it down is giving it gas when its in gear. It really sounds like a thin plate rattling or a tinny bell. If nothing works I will try a new mechanic.


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## goon squad

Are all your zincs tight?


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## cutrunner

Stainless prop?
Could be drive shaft chatter


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## formerWAflyfisher

So I finally took the prop and the thrust washer off and ran the outboard. (If only that's what it was.) No change, still rings like hotel receptionists bell. I was going to start taking things apart and then I remembered I don't know what the hell I'm doing and I have finals in two weeks, suppose to move next week and get married in three weeks. Sometimes I forget things. (selective memory is a b%#%) ;D ;D ;D

Any one know a good Merc mechanic in the Naples area? The prop is aluminum. Cut could the drive shaft rattle that much when not in gear. I didn't feel rattle/anything when I touched it. It's funny because the motor runs fine no hesitation going into gear or when you give it gas. And all the zincs are fine.


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## cutrunner

With an aluminum prop you won't have any chatter, so that rules that out.
worst case scenario you could remove the lower unit and start the motor (no longer than 15 seconds), just to rule out the engine and guarantee it is the lower unit


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## Guest

Had a rattle from a 115 Merc that wasn't coming from the outboard even thought it sounded like it, but the bolt that keeps the steering linkage together at the bottom front of the cowling was loose. Bought an extra few parts because if that goes & the steering locks the motor to one side or the other at WOT you're gonna get wet or worse!


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## hancer67

formerWAflyfisher said:


> Ok so I had this motor serviced about 6-8 months ago because it was making this noise and it stopped for awhile. Now its back. The mechanic did a normal yearly service and charged me to fix a backing plate that was broken. He said there is a plate between the prop and the housing that rattles and make a noise that sounds like a bell. Something about the 2-300 dollars he charged for this item/installation and the way he described it didn't sit well. Not looking to bash I just paid the man and will never go back. Well the noise is back it sounds like the lower unit has a bell that rings at idle. Any insight as to what is making this noise and how to stop it or just live with it.
> 
> 
> sounds like the exhaust baffle plate is cracked or broken
> 
> It's much louder in person than in the vid. It's a 2010 mercury 40 four stroke, With a naturally polished and reshaped aluminum prop.:


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## hancer67

sounds like the exhaust baffle plate is cracked or broken thats what mine was had a boat shop tell me it was a valve wanted to soak me 1600 bucks


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## devrep

7 year old thread. may be good info though.


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## andy race

even though its an old post, for what it's worth i would second an exhaust adapter plate especially if the motor has ever overheated, easy to determine by removing the lower unit cowlings and running the engine, however be VERY CAREFUL as the pinion shaft will be exposed and is always turning when engine is running. early merc 4 strokes had this problem, supposedly corrected on later models


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## Brianr

formerWAflyfisher said:


> Ok so I had this motor serviced about 6-8 months ago because it was making this noise and it stopped for awhile. Now its back. The mechanic did a normal yearly service and charged me to fix a backing plate that was broken. He said there is a plate between the prop and the housing that rattles and make a noise that sounds like a bell. Something about the 2-300 dollars he charged for this item/installation and the way he described it didn't sit well. Not looking to bash I just paid the man and will never go back. Well the noise is back it sounds like the lower unit has a bell that rings at idle. Any insight as to what is making this noise and how to stop it or just live with it.
> 
> 
> 
> 
> It's much louder in person than in the vid. It's a 2010 mercury 40 four stroke, With a naturally polished and reshaped aluminum prop.:


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## Brianr

andy race said:


> even though its an old post, for what it's worth i would second an exhaust adapter plate especially if the motor has ever overheated, easy to determine by removing the lower unit cowlings and running the engine, however be VERY CAREFUL as the pinion shaft will be exposed and is always turning when engine is running. early merc 4 strokes had this problem, supposedly corrected on later models


It’s the driveshaft housing plate. Take the corrosion anodes off, stick your finger in there and rattle away. Sound s just like dinner bell.


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## Brianr

Brianr said:


> It’s the driveshaft housing plate. Take the corrosion anodes off, stick your finger in there and rattle away. Sound s just like dinner bell.


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