# Sound dampening under motor cowling



## DiveLiberty (Mar 3, 2019)

I run a 1978 Johnson 35 hp. The motor is in pretty good shape and I’m trying to my best to get it cleaned up. 

The foam that lines the inside of the motor cowling is largely missing or deteriorated. I’d like to get it cleaned up, especially for the benefit of noise reduction. Obviously a 40 year old 2-stroke will be loud, but if there is anything I can do to improve it, I’d like to give it a shot. I did a quick google search and found a few options and one fella said that he had luck with rubberized undercarriage spray coating. Anybody have luck with this as a replacement for old foam? Would you have any hesitations with using this stuff? 


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## nccatfisher (Mar 3, 2019)

You can use the stuff that they put in cars to keep road noise down. It has a foil on one side and rubberized on the other, they are kinda proud of it.


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## DiveLiberty (Mar 3, 2019)

I’ve seen that stuff, Dynamat. Probably $75-$100 to do my little motor. Spray can is $6 so I may risk it. 


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## Weldorthemagnificent (Mar 4, 2019)

Never used any in an outboard application but McMaster-Carr sells sound absorbing insulation in various sizes. I'd think that and some aerosol adhesive like 3M might accomplish what you need. 

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## Pappy (Mar 4, 2019)

I really do not think the undercoating idea would do you much good compared to the dedicated sound deadening material. The guy that did that is likely to tell folks it did a great job whether it really did or not. A sheet of 1/2" foam, spray adhesive and some silver tape wouldn't kill anyone's budget.


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## DiveLiberty (Mar 4, 2019)

Pappy said:


> I really do not think the undercoating idea would do you much good compared to the dedicated sound deadening material. The guy that did that is likely to tell folks it did a great job whether it really did or not. A sheet of 1/2" foam, spray adhesive and some silver tape wouldn't kill anyone's budget.



I'm sure you are correct. Not sure if I care enough to spend the money on foam. If anything, I just need to tear the foam out and clean up the inside of the cowling before it starts falling off and makes a mess of the motor. Thanks for your thoughts!


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## DiveLiberty (Mar 4, 2019)

That being said, I just found this on Amazon that may do the trick. 10 square feet may be all I need. 

https://www.amazon.com/Noico-deadening-Automotive-Insulation-dampening/dp/B01KZ5X7KO/ref=pd_lpo_vtph_263_tr_t_2?_encoding=UTF8&psc=1&refRID=1YMPQZDM9WBH30HGG91Q


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## DaleH (Mar 4, 2019)

FWFW I have done a V4 & V6 OB, using the lead-lined foam w/ foil and it did work. For even better results, the side cowlings/panels should be done too.


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## DiveLiberty (Mar 4, 2019)

DaleH said:


> FWFW I have done a V4 & V6 OB, using the lead-lined foam w/ foil and it did work. For even better results, the side cowlings/panels should be done too.



Thanks Dale. Lead-lined being Noico/Dynamat type of stuff? Or is that something different?


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## MrGiggles (Mar 4, 2019)

This is a cheaper alternative to Dynamat. Made of the same stuff.

https://www.lowes.com/pd/Peel-Seal-Instant-Waterproof-Repairs-6-in-x-25-ft-Aluminum-Roll-Flashing/1018733?cm_mmc=src-_-c-_-prd-_-lbm-_-google-_-lumber_and_building_materials-_-dsa_lbm_103_building_materials_-_exteriors-_--_-0-_-0&k_clickID=go_910532388_44755799199_312298913908_aud-305162224742:dsa-349678938381_c_9023725&gclid=Cj0KCQiAtvPjBRDPARIsAJfZz0oc2gTUOhKusdQX3cvoBvziG7Ulzrt5WLz6P7AgWS8DjZyL0caYfwYaAk2UEALw_wcB


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## onthewater102 (Mar 4, 2019)

I used an adhesive backed neoprene rubber sheet material, which seemed (as best I could tell) to be what was used on the inside of whichever model newer cowl I looked under for ideas...

https://www.amazon.com/Neoprene-Sponge-Rubber-Sheets-Various/dp/B074HQ9TBP/ref=sr_1_5?keywords=neoprene+rubber+sheet&qid=1551729727&s=gateway&sr=8-5


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## DiveLiberty (Mar 4, 2019)

onthewater102 said:


> I used an adhesive backed neoprene rubber sheet material, which seemed (as best I could tell) to be what was used on the inside of whichever model newer cowl I looked under for ideas...
> 
> https://www.amazon.com/Neoprene-Sponge-Rubber-Sheets-Various/dp/B074HQ9TBP/ref=sr_1_5?keywords=neoprene+rubber+sheet&qid=1551729727&s=gateway&sr=8-5



Thanks. Has this held up to heat okay? How significant of a difference did it make sound wise?


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## onthewater102 (Mar 4, 2019)

It's been on for 2 or 3 seasons so far, and it really made a difference in my late 80's 2 stroke. I may have linked the wrong foam, this is what I bought based on my order history:

https://www.amazon.com/gp/product/B001GAD5G4/ref=oh_aui_search_asin_title?ie=UTF8&psc=1

The OEM foams only hold up for 10 years or so before they dry out and flake away, I wouldn't expect anything under there to be permanent.


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## DiveLiberty (Mar 4, 2019)

onthewater102 said:


> It's been on for 2 or 3 seasons so far, and it really made a difference in my late 80's 2 stroke. I may have linked the wrong foam, this is what I bought based on my order history:
> 
> https://www.amazon.com/gp/product/B001GAD5G4/ref=oh_aui_search_asin_title?ie=UTF8&psc=1
> 
> The OEM foams only hold up for 10 years or so before they dry out and flake away, I wouldn't expect anything under there to be permanent.



Thanks. It's good to hear from someone who has actually tackled this project. The older 2-strokes are pretty noisy. I know it comes with the territory with 2-strokes, but I don't mind giving it a shot. 

One more question, did the adhesive alone stick okay, or did you have to add some spray adhesive as well?


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## Weldorthemagnificent (Mar 4, 2019)

I think that motor exhausts out the back above the water doesn't it? They went to through hub shortly after I believe. The exhaust location makes a difference in the noise. I had a 76 20 hp. Same motor, weighed 98lbs. Awesome motors. 

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## DiveLiberty (Mar 4, 2019)

Weldorthemagnificent said:


> I think that motor exhausts out the back above the water doesn't it? They went to through hub shortly after I believe. The exhaust location makes a difference in the noise. I had a 76 20 hp. Same motor, weighed 98lbs. Awesome motors.
> 
> Sent from my CLT-L04 using Tapatalk



Yes, it does exhaust out the back, which you're right is a big factor.


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## DaleH (Mar 4, 2019)

DiveLiberty said:


> DaleH said:
> 
> 
> > FWFW I have done a V4 & V6 OB, using the lead-lined foam w/ foil and it did work. For even better results, the side cowlings/panels should be done too.
> ...


I believe it was from 'SoundDown', but not sure they are still in business or sell it, if they are. Defender Marine in CT sold it.


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## onthewater102 (Mar 4, 2019)

I too applied the material to the entire interior of the cowl. 

The engine noise you hear that you can control most is actually intake noise amplified with the carburetor throat acting like a megaphone. I snagged a plastic baffle off the newer mercury 25hp carbs that really helped simply deflecting some of that noise to the sides, not sure if something similar is an option for you with that motor.

I couldn't find a picture of the piece added to my carb, but here's an image of a newer 25hp carb with a noise deflector (black plastic snorkel looking part)


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## Pappy (Mar 4, 2019)

Onthewater is absolutely correct on where the bulk of the noise comes from on a 2-stroke! 
For what it's worth, different years had an air silencer that can be sourced and installed but nothing wrong with the Merc one from the looks of it if it will fit.


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## onthewater102 (Mar 5, 2019)

Oh I wasn't trying to imply the merc parts would fit the old Johnson - just provide a visual as to what it is in case he couldn't find a corresponding OMC part and tried to fab something himself.


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## DiveLiberty (Mar 5, 2019)

onthewater102 said:


> Oh I wasn't trying to imply the merc parts would fit the old Johnson - just provide a visual as to what it is in case he couldn't find a corresponding OMC part and tried to fab something himself.



Great info, thanks for sharing.


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## DarrellS (Mar 13, 2019)

Hi Onthewater : Did you notice a reduction in noise with that air silencer . The previous owner removed all the sound deadening material from engine on my my boat so this thread caught my attention , The noise from the carburetor bugs me sometimes .
I have tried to find the part you are using but it seems to be unavailable ( 853728 1 - COVER )


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## onthewater102 (Mar 16, 2019)

It made a significant difference. You could easily fab something similar as long as it'll take a little heat without deforming and reflect the noise coming out of the carb so it's not directed straight into the boat. I believe I found mine watching ebay for a bit, they come up every so often as people are clearing out old stock.


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