HOME GENERATOR - Muffler Defective

[mtnelect]

I have a small 4K, 240 Volt home generator, where the connection has separated from the muffler. I was wondering if this was an opportunity to install a larger muffler to quiet the sound. I have seen flexible conduit made for high temperature rated connections for exhaust applications. It looks like a 1" connection from the engine to the muffler. Is this possible to extend from the engine to a new muffler, without damaging the exhaust pressure problem ?

 

[ptonsparky]

Personally, I doubt if Powermate figured back pressure into it. I can ask one of their former techs if need be.

 

[Birken Vogt]

Briggs engines of that era were made by Briggs to fill specific customer orders and nothing more. They did not do a whole lot of product testing and engineering, so long as most of them made it out of warranty everybody was happy.

I have seen nothing but junk from exhaust connections of that type. The steel flex you can buy is not made for continued flexing and once it gets hot and begins to rust it just crumbles.

Better to see if you can fix what you have.

 

[hillbilly1]

I’ve tried that before with unsatisfying results. You might try a motorcycle muffler, it is designed for a small engine, so back pressure may not be as big of an issue. Something from a 250-350 cc bike.
Maybe a muffler off a motor home generator (Onan)

 

[drcampbell]

For making connections, there's something called "Flexible Metal Hose" that's exactly what you need. It's available in various stainless-steel alloys that will outlast the engine, and in prefabricated assemblies with various standard fittings at the ends.

https://www.grainger.com/product/HOSE-MASTER-Flexible-Metal-Hose-Assembly-4FKK5

Corrugated stainless steel tubing -- without the plastic jacket, of course -- might also be an option if you want to do your own fabricating.

I would expect back pressure in the tubing to be inconsequential. Likewise almost any larger-than-stock muffler.

I'm guessing this is about a 0.3-liter, (0.01 ft³) 3600 rev/min, 4-stroke, single-cylinder engine. That means about 18 standard cubic feet per minute airflow, give or take. Your results may vary.

But more important than flowrate and back pressure is selecting a muffler that's "tuned" for the 30-Hz exhaust note.

Were you to adopt the "bigger is better" design philosophy and grab a muffler from, say, an Oldsmobile Vista Cruiser with an 8-liter engine, you'd more than satisfy the back-pressure requirement, but it might not muffle very well because it would be designed for best performance at something like 120 Hz.

Spiral silencers are quite effective. They have a rather-long flow pathway in a rather-compact package. I don't know if they're available in a suitable size.

TENOR Spiral Silencers - Products - Tehag.com

TENOR Spiral Silencers. The ideal solution for highly effective silencing in small installation spaces.

www.tehag.com

You might also consider a two-stage, muffler & resonator combination.

 

[petersonra]

I have seen several YouTube videos about this exact thing. You might want to search there and see what other people have found that works.

 

[infinity]

I have seen several YouTube videos about this exact thing. You might want to search there and see what other people have found that works.

I've watched many of those videos of from what I've gathered those muffler additions do little to mitigate a significant amount of generator noise. A large portion of the noise from these generators is from the engine and the generator itself.

 

[mtnelect]

As always, great information from all !

 

[petersonra]

I've watched many of those videos of from what I've gathered those muffler additions do little to mitigate a significant amount of generator noise. A large portion of the noise from these generators is from the engine and the generator itself.

Most of the people who successfully quiet generators do so by enclosing the generator in some way.

Was kind of my point.

 

[Joethemechanic]

Engines needing back pressure is a myth.

 

[drcampbell]

Engines needing back pressure is a myth.

mtnelect :​

When you said "the exhaust pressure problem", were you thinking that you might impose too much back pressure, or too little?
A four-stroke engine can never have too little back pressure.

An excessively-short straight stack (or running with no exhaust system) can cause problems by letting oxygen into the exhaust port and causing rapid corrosion of the exhaust valve and seat, but that's not a result of "inadequate" back pressure.

 

[Joethemechanic]

And there are flexes made for connecting engines mounted on vibration insulators to solidly mounted exhaust systems.. Personally I never had a problem with the spiral stuff, but if you don't like it, you can spend a few more bucks and get one of these

 

[mtnelect]

mtnelect :​

When you said "the exhaust pressure problem", were you thinking that you might impose too much back pressure, or too little?
A four-stroke engine can never have too little back pressure.

An excessively-short straight stack (or running with no exhaust system) can cause problems by letting oxygen into the exhaust port and causing rapid corrosion of the exhaust valve and seat, but that's not a result of "inadequate" back pressure.

Too little back pressure, because of too large of a muffler.

 

[Joethemechanic]

Too little back pressure, because of too large of a muffler.

That's not a problem. That whole engines need back pressure thing is a total myth. Engineers work hard to get high volumetric efficiency, back pressure lowers volumetric efficiency.

 

[Joethemechanic]

You even have a carb with an adjustable main jet. No problem at all if you need to adjust the air fuel ratio

 

[drcampbell]

Too little back pressure, because of too large of a muffler.

There is no such thing.

A few engines optimize performance with dynamic management of exhaust back pressure. In single-cylinder applications, such setups are designed to minimise back pressure during the time the exhaust valve is open.

Tuned exhaust - Wikipedia

en.wikipedia.org

This Coleman generator isn't one of them. It doesn't even have overhead valves.

Designing a tuned exhaust would be a significant research & development project, for which you are not equipped,
It would also be rather pointless. For a 3600-rev/min engine, it would be huge. This engine isn't strong enough for reliable operation at higher power and doesn't have surplus cooling capacity or an oil pump. Even if it were, the generator couldn't utilize the additional power input without radically improving the cooling.

Installing a too-large muffler is likely to result in a disappointing amount of noise reduction, but because it was an off-the-shelf item designed for a multi-cylinder engine with a much higher-frequency exhaust note, not because it's too large. (and because much of the noise generated by a small, air-cooled engine like this originates from the cooling fins)

 

[mtnelect]

There is no such thing.

A few engines optimize performance with dynamic management of exhaust back pressure. In single-cylinder applications, such setups are designed to minimise back pressure during the time the exhaust valve is open.

Tuned exhaust - Wikipedia

en.wikipedia.org

This Coleman generator isn't one of them. It doesn't even have overhead valves.

Designing a tuned exhaust would be a significant research & development project, for which you are not equipped,
It would also be rather pointless. For a 3600-rev/min engine, it would be huge. This engine isn't strong enough for reliable operation at higher power and doesn't have surplus cooling capacity or an oil pump. Even if it were, the generator couldn't utilize the additional power input without radically improving the cooling.

Installing a too-large muffler is likely to result in a disappointing amount of noise reduction, but because it was an off-the-shelf item designed for a multi-cylinder engine with a much higher-frequency exhaust note, not because it's too large. (and because much of the noise generated by a small, air-cooled engine like this originates from the cooling fins)

Thank you all for your reply's ... This is a great forum, where members can ask questions and get an answer to many questions ! I don't have this depth of knowledge to make a decision. So, from what I am hearing, just try and find a similar replacement and don't modify the existing design.

 

[LarryFine]

You could try patching the split with an exhaust sealer putty.

 

[Bill_F]

Excellent viewpoints, thank you!
We DO want reduced noise!!!
However, I have always believed we must consider the engineering aspect, of "swapping in" some "other" muffler, which does quiet, BUT may impact the engine's design somewhat negatively.
Several knowledgeable folks talked about backpressure.
I am sure that is definitely an engineering original design aspect.
I have altered small engines to achieve lower noise for the neighbors... but am not intelligent enough to determine if the difference in back pressure hurts my engines.
Thanks very much!
Bill

 

[PaulMmn]

I have a small 4K, 240 Volt home generator, where the connection has separated from the muffler. I was wondering if this was an opportunity to install a larger muffler to quiet the sound. I have seen flexible conduit made for high temperature rated connections for exhaust applications. It looks like a 1" connection from the engine to the muffler. Is this possible to extend from the engine to a new muffler, without damaging the exhaust pressure problem ?

Growing up our Gravely mowers had mufflers like this. I think the pipe was about 1" (YMMV). Muffler was replaceable (although we still wore Dad's shooting earmuffs while mowing). I think the connection is standard plumbing threads (maybe). You don't want to add excess weight where none is expected! So be careful!