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Exhaust damper plate?
https://www.smwebhead.com/phpBB3/viewtopic.php?f=11&t=15324		 Page 1 of 1
Author:  MikeD [ Wed Feb 22, 2017 8:04 pm ]
Post subject:  Exhaust damper plate?
This is in regards to my previous post regarding low WOT of my 4.3GL (A) Volvo Penta.

I was told by a mechanic to check the lower part of my exhaust system for a damper plate that may have fallen off it's hinge due to excessive overheating. When my engine overheated the rubber exhaust couplings on the port side partially melted. If this is the case, this damper is more than likely blocking the discharge of exhaust gases in the lower unit thereby lowering my WOT RPM's.

I found very little about this subject on the boating forums other than the fact that Volvo discontinued their use. I have a 2000 FW Horizon 190 and I can't recall seeing such a device when I changed out my risers and manifolds. Should I be looking further and were these dampers installed on all V/P engines? Appreciate any thoughts on this subject.
Author:  Thalasso [ Wed Feb 22, 2017 10:49 pm ]
Post subject:  Re: Exhaust damper plate?
MikeD wrote:
This is in regards to my previous post regarding low WOT of my 4.3GL (A) Volvo Penta.

I was told by a mechanic to check the lower part of my exhaust system for a damper plate that may have fallen off it's hinge due to excessive overheating. When my engine overheated the rubber exhaust couplings on the port side partially melted. If this is the case, this damper is more than likely blocking the discharge of exhaust gases in the lower unit thereby lowering my WOT RPM's.

I found very little about this subject on the boating forums other than the fact that Volvo discontinued their use. I have a 2000 FW Horizon 190 and I can't recall seeing such a device when I changed out my risers and manifolds. Should I be looking further and were these dampers installed on all V/P engines? Appreciate any thoughts on this subject.



Volvo hasn't used flapper in the exhaust since 1999. In fact there was a service bulliten that said not to replace them if they were destroyed. If you remove the drive (if they were in there) this is where you most likely will find them in the exhaust
Boating in Salt water?( SW Florida) Maybe your risers are clogged and creating an overheat.
17 years is a long time on risers. Salt you would be lucky to get 6-7
Author:  MikeD [ Thu Feb 23, 2017 8:47 am ]
Post subject:  Re: Exhaust damper plate?
Thanks for the reply. I did replace both risers and manifolds after overheating. You mentioned that Volvo hasn't used exhaust dampers since 1999 and although my boat is a 2000 model year, my engine was built in 1999. How can I tell whether or not dampers were originally installed?
Author:  Surface Interval [ Thu Feb 23, 2017 10:11 am ]
Post subject:  Re: Exhaust damper plate?
If your boat came with flapper valves they are most likely installed in the top end of each side of the "Y" pipe. The Y pipe is is just after the exhaust high rise manifold and elbow. You can access this area by loosening and sliding each rubber hose connector on the exhaust elbow so the elbow can be removed. First you might try removing the anode on the bottom side of the transom shield and also disconnecting the exhaust bellows from the transom shield. Use a flashlight to look forward in the exhaust passage through the transom for the flapper valve. You may also find the Stainless Steel flapper hinge pin. The exhaust passage is smaller in diameter in the transom area and the flapper valve will not pass through into the outdrive. If you find one, you will need to remove the exhaust elbow and try to connect a wire and pull it up the y pipe to remove it. Here is a pic of the side of a typical engine/drive. When re-installing the exhaust elbows, make sure that the elbow's lower hose is positioned over the mounting holes for the flapper valve and that the lower hose clamp tightens the hose to seal these holes. I learned from experience on this one when I heard water dripping in the engine compartment.
http://www.boattest.com/images-gallery/ ... -thumb.jpg

Here is a pic of a Volvo flapper.
Image

See items 41, 42, and 43 on this link:
https://www.marineengine.com/parts/omc- ... /56985.gif


Here is a link to a previous discussion. I did have this problem on my previous boat. The flappers in my '95 190 Horizon were a rubber coated metal. I am puzzled when people say they melt. They operate for hundreds of hours in the exhaust flow, but then people say when they come loose they travel down stream in the exhaust system to where the exhaust flow is cooler and then they melt??? Doesn't make sense. I experienced very similar symptoms. 4000rpm max and 40 mph at top end instead of the normal 4600 and 52-54 mph. The boat was a DOG with the flapper significantly restricting exhaust flow. It ran very smooth, but just didn't have its normal power.
viewtopic.php?f=3&t=15053&hilit=Flapper+valves

Hope this helps.
Author:  LouC [ Thu Feb 23, 2017 7:15 pm ]
Post subject:  Re: Exhaust damper plate?
Unless there were different styles, mine looked exactly like that. And when I had an overheat, they were vaporized. No metal inside at all. I found them at the bottom of the Y pipe after I remove the outdrive. I did replace mine but not sure if they really help.
Author:  rpengr [ Fri Feb 24, 2017 8:30 am ]
Post subject:  Re: Exhaust damper plate?
Surface Interval wrote:
...I did have this problem on my previous boat. The flappers in my '95 190 Horizon were a rubber coated metal. I am puzzled when people say they melt. They operate for hundreds of hours in the exhaust flow, but then people say when they come loose they travel down stream in the exhaust system to where the exhaust flow is cooler and then they melt??? Doesn't make sense. I experienced very similar symptoms. 4000rpm max and 40 mph at top end instead of the normal 4600 and 52-54 mph. The boat was a DOG with the flapper significantly restricting exhaust flow. It ran very smooth, but just didn't have its normal power.
viewtopic.php?f=3&t=15053&hilit=Flapper+valves

Hope this helps.


My previous boat (1987 OMC Cobra like LouC's) had rubber flapper valves. There was no metal in them except the shaft. They don't melt if there is some water flow through the exhaust manifolds because they would get sprayed with liquid water (less than 212F) along with the hot exhaust. If you lost water flow due to a waterpump problem or a clogged manifold then you could melt the rubber.

The interesting thing is that with a partially obstructed exhaust, the engine will run perfectly smooth. It is similar to not getting full throttle because of a throttle linkage not opening all the way. (reduced air out has the same effect as reduced air in)

I had an airplane lose about 15% of it's power because of a muffler problem. It was very gradual, so it took a while before it was detected.
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