How to make an old engine quieter...

[samo_ott]

So has anyone tried adding in a pee hole on the old 50's or 60's engines by drilling and tapping the water jacket? Then what would happen if you plugged up the exhaust outlet halfway up the leg? I believe the main reason for that outlet is to see the cooling water exit. But if you had a pee hole then you wouldn't need it. In theory.

Thus if you plugged it you would get rid of a lot of exhaust noise that also comes out through it and make it all go underwater like a thru hub'er. If you ever lean over and plug that hole with your thumb you will see what I mean. (I tried it 2 days ago on my 18hp and it is quieter) The only issue I could see is if when in reverse there's no exhaust relief by using this method and it could build up exhaust pressure.

Has anyone ever tried this? And comments, modifications or upgrades? It was just a thought I figured I'd throw out to the community.

 

[Vic.S]

Re: How to make an old engine quieter...

If the exhaust relief holes where blocked wouldn't the back pressure make starting difficult. I thought that was their purpose not to provided a (poor) indication of water flow

There are instructions in the FAQs for adding telltales but engines that have telltales still have relief holes and even engines where the cooling water discharges directly from the power head in a visible stream rather than into the leg still have relief holes. Air cooled engines as well and engines with no reverse.

 

[samo_ott]

Re: How to make an old engine quieter...

One of the things that made me think of it was my 1950 Evinrude 7.5 hp has no above water exhaust discharge. It has only a water exit. All exhaust discharges underwater. BUT, there is no reverse on it, you are must rotate the engine for reverse which means that you would never get water pressure going against the water flow...

 

[wbeaton]

Re: How to make an old engine quieter...

You need the exhaust port in the leg to release back pressure at idle. However, I have also wondered about installing a tell tale. Just out of curiousity.

 

[jbjennings]

Re: How to make an old engine quieter...

Well,
Where I live there's so much tiny plant matter in the water that I actually like not having a tattle-tail hole because they get stopped up with crud and constantly make me nervous when they do. The exhaust relief never gets stopped up which is better for me. Also, my '53 johnson 25hp has already made me deaf so I'm immune to motor noise, now!
JBJ​

 

[Chinewalker]

Re: How to make an old engine quieter...

The hole in the leg is NOT a tell tale, rather it is an exhaust relief. The water outflow from there is actually for silencing purposes so that you're not getting dry exhaust out that hole. It has to be open for the motor to perform properly...
- Scott

 

[samo_ott]

Re: How to make an old engine quieter...

You need the exhaust port in the leg to release back pressure at idle. However, I have also wondered about installing a tell tale. Just out of curiousity.

My 1950 Evinrude 7.5hp has no exhaust relief. It all goes underwater and it idles great. Photo attached (ignore the color - I got it that way - some poor sod must have really wanted a Merc!) You can see the pencil sized stream of water exiting the housing a few inches above the water line. That is the only above water exit of anything.

We're all lead to believe that it needs exhaust relief as we always hear that but if the 7.5 does not need it, why do others need it? I can see a problem if it had reverse but it does not...

In addition, when I stuck my thumb over the hole on my E18hp it still ran fine at idle... Mind you I did not hold it there long as I was hanging off the back of my pontoon boat to do it....

 

[wbeaton]

Re: How to make an old engine quieter...

Nice Merc.

I've never run one with the mid-section exhaust plugged up nor am I an engineer, but I would assume the increase and then subsequent release of built up exhaust in the mid-section would cause it to idle erratically. I expect if it didn't need the exhaust relief the good folks at OMC would have saved a few bucks and omitted it.

 

[EricR]

Re: How to make an old engine quieter...

Sammo, what is that raft made from and how fast does that 7 and a half push her?

 

[samo_ott]

Re: How to make an old engine quieter...

It doesn't go as fast as one would think. It's two sailboards bolted together by a welded aluminum frame with 4'x7'plywood and carpet on top and a transom.