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Rattle in exhaust manifold

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Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
Printed Date: May-21-2024 at 9:08am

Topic: Rattle in exhaust manifold
Posted By: Rob-Man
Subject: Rattle in exhaust manifold
Date Posted: June-28-2023 at 8:57am
The 86 SN 2001, has a rattle on the right exhaust manifold at idling speed. when I put a little throttle on it goes away.  it was intermittent at first now its steady at idle speed.  sounds like something is bouncing around in there.  engine time is fine, never above 150.  I was thinking about taking the top of the manifold off and looking in there, any ideas for the neophyte? 

Posted By: Rob-Man
Date Posted: June-28-2023 at 10:29am
I replaced the impeller earlier this year, could this be the culprit?

Posted By: KENO
Date Posted: June-28-2023 at 12:07pm
I don't think you'll hear rubber "rattling"

AN 86 has fiberglass mufflers with baffles inside and if a baffle like the upstream one breaks off it makes a funny rattle in the exhaust system that can fool you as far as where it's coming from. The rattle is more pronounced at idle speed .

Finding that would be done with your ear real close to the muffler or using a stethoscope or screwdriver on the muffler with the other end up to your ear.

It's worth a listen Wink

Posted By: Rob-Man
Date Posted: June-28-2023 at 12:43pm
Thank for the reply Keno. Are the baffles inside the exhaust manifolds?  Can I fix the rattle by taking the riser off and removing the loose piece?

Posted By: KENO
Date Posted: June-28-2023 at 12:52pm
Baffles are in the mufflers under the removable floor piece.

They're fiberglass like the muffler, but it makes quite a noise as they rattle around.

There aren't any pieces in the exhaust manifold or riser that would rattle, unless you have some giant chunks of rust flakes from years of corrosion. They usually settle at the back of the manifold where the big drain plug screws in though.

Any chance it's a lifter noise or an exhaust leak you're hearing, if it's definitely up in the manifold area?

Posted By: Rob-Man
Date Posted: June-28-2023 at 1:04pm
Mufflers are here, didn't realize that's what that was.  I will dig into it more tonight.  let you know what I find. 


Posted By: AZ86SKI
Date Posted: June-28-2023 at 5:39pm
Here is the view looking in from the exhaust port on my 86SN. The photo is not the best but perhaps it's helpful. When you look closely there should be two baffles on each side as KENO stated." rel="nofollow">

Posted By: Rob-Man
Date Posted: July-01-2023 at 11:44am
I did more trouble shooting, i am leaning towards circulating water pump.  

Posted By: KENO
Date Posted: July-01-2023 at 1:19pm
Take both belts off and fire up the engine and see if the noise is still there. It'll take the circulating pump, raw water pump and alternator and their belts out of the picture

10 to 15 seconds or so won't hurt anything and you should know if the noise is still there or not 

While they're off you'll also be able to spin the circulating pump and the alternator by hand to see if they're making noisy bearing type noises Raw water pump is a little harder to "spin"

Then you can check the condition of the belts and pulleys too.

Posted By: bwinn
Date Posted: July-02-2023 at 9:54am
Possibly a bad damper plate?

Posted By: Rob-Man
Date Posted: July-05-2023 at 4:15pm
I took both belts off, started the engine and the rattle is still there.  What is a damper plate, and how do i trouble shoot?  

Posted By: bwinn
Date Posted: July-05-2023 at 4:47pm
Damper plate is bolted to flywheel at rear of engine and connects flywheel to input shaft of your velvet drive. It has springs that wear out and can become loose or even fall out.

Possibilities besides failure of plate
-idle too low

Posted By: Rob-Man
Date Posted: July-05-2023 at 4:52pm
wish i could post a video of the rattle but i can't. 

Posted By: Rob-Man
Date Posted: July-05-2023 at 5:30pm
Thanks Bwinn, Looks like we are leaning towards damper plate. 

-idle too low -  No
-misfire - No

Posted By: KENO
Date Posted: July-05-2023 at 6:47pm
I guess it's a mystery noise from.............well, somewhere under the engine box Wink

Whatever your idle speed is now, temporarily bump it up a hundred or so RPM and see if you still have the rattle at idle speed.

What's your idle speed in gear when it's rattling? and what speed does it go away at?

Try listening with the stethoscope, screwdriver etc mentioned earlier in the thread on the top of the bellhousing. there an ending that you must have forgotten to write for the thread in the link below?" rel="nofollow - link

Posted By: fanofccfan
Date Posted: July-06-2023 at 8:40am
I had manifold gaskets that made me change a good but old enough damper.  Felt rather silly about the mis diagnosis but in the end both probably needed attention.  However, Manifold gaskets were my rattle.  In fact, the exhaust ports were burned so bad that I used high temp Jb weld to make them true as well as having the manifolds planed.  Backyard hack for sure with the JB but its been working so far.

2004 196 LE Ski 1969 Marauder 19 1978 Ski

Posted By: Rob-Man
Date Posted: July-06-2023 at 9:12am
i have a mechanic friend coming out tonight to help with diagnosis.  is a damper plate replacement something I can do on the boat on a lift?  the video i watched was little intimidating for a neophyte. 

Posted By: Rob-Man
Date Posted: July-07-2023 at 12:40pm
we looked at it again started without the belts on, couple times.  He (more mechanical inclined friend) is thinking it's a timing chain rattle.  it's coming from behind the crankshaft pulley.  towing boat out to ramp tomorrow and taking to shop.   

Posted By: Rob-Man
Date Posted: July-13-2023 at 11:42am
I can't find anyone to work on this boat.  I am in the St. louis area. does anyone know of anyone close? 

Posted By: KENO
Date Posted: July-13-2023 at 9:00pm
How many hours are on the engine? Timing chains last lots of hours.

Before just assuming the noise is the timing chain, I'd look at the fuel pump.

Take it out and see if the actuating lever is worn, maybe it has a broken spring letting the lever rattle around as it operates

It just happens to be right in the same neighborhood as the timing chain and it a lot easier to replace Wink

Posted By: Rob-Man
Date Posted: July-14-2023 at 9:08am
Not many hours on this engine at all. around 300.  I will check that out.  Thanks.

Posted By: KENO
Date Posted: July-14-2023 at 9:57am
At 300 hours your timing chain shouldn't be an issue at all.

I'd for sure look at the fuel pump and also pop the distributor cap off to see if there's anything out of the ordinary going on in there.

Since we can't hear the noise, it's hard to really tell very much, but 300 hrs is nothing to the timing chain and gears.

Posted By: KENO
Date Posted: July-14-2023 at 2:42pm
Somebody out there that can post a video if it gets sent to you?

Rob sent it to me, so either of us could send it to you for posting on YouTube or whatever.

Posted By: Rob-Man
Date Posted: July-14-2023 at 4:42pm
Thanks for the insight, Ken.  I will send to anyone who wants to post it and give me your thoughts.  this is a tough one for a rookie like me. 

Posted By: Rob-Man
Date Posted: April-02-2024 at 4:37pm
I finally had a person diagnose and is fixing the issue.  The rattle was caused by bearing in the drive shaft, right coupler.  FINALLY!!!!  closer on this issue.    

Posted By: KENO
Date Posted: April-03-2024 at 7:07am
Originally posted by Rob-Man Rob-Man wrote:

  The rattle was caused by bearing in the drive shaft, right coupler.   

I'm pretty sure that I don't know what bearing is being talked about Wink

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