I have an old lawn tractor that I want to make quieter. It has a single cylinder
Briggs & Stratton 8hp engine that has a muffler that doesn't muffle. I replaced
that one with one for a 9-16hp B&S engine, but it didn't get any quieter. These
seem to do nothing except provide back pressure.
Anyone have a design for a muffler that will make it possible to talk with the
engine running without shouting?
You can reduce the noise with a better muffler, but keep in mind it fires
every cycle. I KNOW its not a 2 stroke BUT it does fire on every stroke. the
motor fires both on compression and exhaust, and it fires at some point
before TDC so the exhaust valve is just about shut when it fires.
Blink. Blink. Fires?
I don't think so. It may provide spark on every cycle, but it has nothing
to burn for it to "fire". It's discharging the spent air/fuel mixture that
fired on the previous cycle. I certainly can't imagine the spark creating
that kind of noise. Unless something is woefully wrong with the engine, the
gasses contained within the cylinder on the exhaust stroke won't ignite.
Air cooled engines tend to be noisier than water cooled engines. I imagine
the engine in question is air cooled. Years ago I converted an 8 horse
air cooled Kohler engine to a water cooled engine. It ran much quieter.
The water jacket provides considerable damping.
I had a left-over bullet-style muffler (not a glass-pack straight-thru,
but a real 3-chamber muffler) from another project, so I put it on my
16 Hp Wisconsin one-lung tractor engine. It definitely helps, but it
really doesn't reduce the total noise, just moves the sound spectrum.
It goes from an ear-splitting gunshot rat-tat-tat to a low bum-bum-bum,
that is a lot more tolerable. But, I'd like to reduce it more. Still,
it helps a lot. I managed to ram into something and broke the fitting
off last fall, so I got a reminder of how loud it was without the
You don't need quite so big a muffler with your 8 hp engine, so you
might be able to find something for commercial lawn machines, or
other small engines that will do the job.
If you really want to go insane and BUILD one, you might need a TIG
welder or something like that. Look at a real muffler, like on a car.
They have three chambers, connected by perforated pipes. The gases
expand out of each pipe into the next chamber, then into a pipe to
the next chamber, etc.
i was very proud of a "muffler" i made for my 7 hp kohler troy-bilt roto
tiller. what a crappy muffler it used to have, rusted out in no time,
replaced it and rusted out again, quickly. it then became just a short
empty tin can with louver slots cut in it. finally got SICK of the NOISE
and having the exhaust fumes blowing directly in my FACE when i was tilling.
cut a mounting flange out of 1/2" steel plate (the oblong thing with the big
hole for the exhaust and two 1/4" holes on both sides for bolts to go
through) and carefully prepared a expended (hand held style) propane tank
(threw it into a huge bon-fire) (and quickly walked far away). welded an
elbow from the flange to the propane tank, then another elbow to a 9 inch
long extension to route the exhaust down and forward below the wheels and
out toward the front. terminated the exhaust pipe with multiple 1/2" holes
through the side of the pipe in an attempt to "break up" the exhaust gases
and noise and direct the fumes forward instead of straight down into the
dirt. the propane tank has no baffles inside, and i don't think it needs
any but prolly would (with further effort) be even quieter with baffles. it
made the tiller go from NOISY to darn near quiet. i was concerned it might
affect the performance of the engine or harm it in some way but i think any
reduction in performance is negligible. a lot of work though. for me it
was worth it. i'm still pleased with that muffler every time i use the
tiller. looks cool too.
No. The cylinder was mounted on a rotary table so the fins could be either
reduced or eliminated, using a stub arbor and a side cutter, then a
stainless band was fabricated that was held by a pair of stainless hose
clamps. The top and bottom fins were left almost full size in order to
create the water area between them. The fins didn't go all around, so the
jacket terminated with pressure pads. It worked like a charm. Made a new
head from aluminum, and a water pump. This went into a boat that didn't
have room for a commercial power plant. It drove an 80 amp alternator and
worked flawlessly as long as we had the boat, which had an electric
refrigerator, the reason for the needed additional charging capacity. I
have pics if you're interested. Let me know and I'll forward them to you.
"William Wixon" wrote in
That sounds like a fun project. As a simpler solution I've started wearing
a pair of cheap earmuffs whenever I run something loud. It is so nice to
finish cutting the grass and not have ringing ears.
My mower exhausts right our the front grille, pointing forward.
Yours probably does something similar. I think adding tubing to route
the exit into the grass would be very beneficial. Thickwall tubing would
be better than thin, though harder to work with. Support would be
critical, otherwise harmonics would make the noise worse, and it would
crack in short order.
Even better would be dumping it into the mower deck interior where
the exhaust pulses could be mixed into the maelstrom therein. But that
adds an extra level of complexity, allowing for deck adjustment. Still
if the deck moves perfectly vertical, you could make the exit vertical
so it slips through. If not vertical, you would have to match the angle
of movement. Usually there is an area in the periphery of the deck
where no blades reach.
Of course, I haven't done this :)
No charge for this consultation.
I wouldn't mind seeing a picture or two of that Harold.
The the OP, I got a box of earplugs and I dig a pair out when it's time
to run the lawn equipment.
It might be that you've got too big of a muffler on it- can't get enough
backpressure to really break up the impulses..
A neighbor had me help with the small amount of welding needed to adapt
a Honda generator muffler to fit his B&S powered generator. All that
was needed was to fabricate the elbow to mate the different style
flanges and to fill the 6 or 8 holes in the muffler case that I presume
were for some bracketry on a Honda generator.
I didn't hear the results, but the owner was happy with the
improvement. The generator was used for camping at shows and swap
meets where quiet makes for good neighbors.
I'm curious how you did this. Weld up a water jacket around the cylinder?
Very interesting, thanks. Another thing comes to mind with this kind of
conversion. I know that engines are engineered to operate at certain
temperatures for efficiency. Wouldn't a conversion as you describe have
changed the operating temperature to such a drastic degree to upset that
efficiency? Or isn't that the case with air cooled engines?
Ringing ears you say?! I have those all the time thanks to my working at
Boeing on the 767 wing line. And yes I was wearing ear protection, two
actually; foam ear plugs and headset. The noise was so loud when we were
riveting wing panels that you could feel your chest vibrate. That wing panel
acted like a huge drum skin.
I noticed that the mowers that commercial landscape service guys use around
office buildings are quieter than the same mufflers used on homeowner
mowers. Now why they can't put those mufflers on the homeowner mowers?
When I was young I think the after effect was more like a hissing, but
as I have gotten older it has gotten more like a ringing. If I'm not
careful and do something especially loud they will sometimes ring for
several days. My Dad did aircraft work and ended up quite deaf.
In my opinion, for what it's worth, yes, the operating efficiency is and was
altered, likely not anywhere nearly as good as it may have been, but I had
no alternative. It was important to get a functioning generator because
we had two dead batteries almost constantly. While it was likely harder
on fuel running slightly cooler, imagine what it was costing us to run
around Lake Powell for hours just to charge our batteries. We'd go
through 80 gallons of fuel in a day. From all indications, we could run
the power plant for hours on just a couple gallons of gasoline. A much
better deal, and we didn't have to have the boat in motion to do so. At
night, when we sat around a big fire, sipping scotch and listening to music,
I'd run it to get the batteries fully charged for the night. By then, I
had installed yet another battery, so we had three. The third was isolated
from the other two and used for only light duty, assuring we had power to
start the generator should the other batteries puke.
One of the things I did was to go to a hotter plug, so it wouldn't foul
prematurely. I'm not convinced even that was necessary. As I said, we had
absolutely no problems with the unit, which we used for several years. It
was still functioning flawlessly when we sold the boat back in '90.
I had tried an earlier version of the power plant, using an air cooled
engine. Even with a second blower running, the engine compartment got way
too hot. By going to the water cooled engine, including a water cooled
exhaust system, that was no longer a problem. I ran the second blower
alone afterwards, and it kept the engine compartment at an acceptable