Lawnmower exhaust

[rich r]

Does anyone have any experience of replacing the box type exhaust muffler on a Briggs and Stratton ride on lawnmower engine with a moped/motorbike/quad silencer? I've seen a few on US sites where this has been done, but wondered if anyone here has any knowledge to share regarding what might work and what might not.

I'm just looking at ideas to quieten down my 190cc 6.5hp engine a little, and also redirect the exhaust gas so it's not pointing straight at the deck height lever making it hot. I could probably squeeze in a small silencer and have the gas exit further back.

Of course this could be a silly idea and it won't work out any quieter but I thought I'd ask...

 

[pedrobedro]

A friend of mine made a box exhaust just using thicker metal for his 4 stroke mower and it works well and is quieter. He just copied the rotted original.

 

[jimmyspeed]

you could make a simple glass fibre one like motocross bikes use. Essentially a large pipe (or box) with a perforated tube running throughout the centre. The fibre glass is packed around the outside of the perforated pipe and an end cap is screwed in place. simple and light

 

[Paul99]

you could make a simple glass fibre one like motocross bikes use. Essentially a large pipe (or box) with a perforated tube running throughout the centre. The fibre glass is packed around the outside of the perforated pipe and an end cap is screwed in place. simple and light

I made one like that for a 16hp Kohler engine many years ago and it worked to a certain extent in that it sounded a bit softer (only a bit though) but was a flawed design in that I had to put a 90 degree bend in the pipe - a simple mitre restricted flow and cut engine power a bit so gave up on it and it's run without anything since. I found the original silencer a few weeks ago which consisted of perforated entrance / exit pipes terminating in separate chambers within the silencer which from what I read performs better than a glass pack. If I can't patch up the original I'll look at making one similar as after 10 years I'm now starting to get fed up of the noise.

 

[rich r]

Hmm, yes, I'll need a 90 degree bend for any silencer to lie along the side of the engine. I wonder then if I'm better off looking at making a replacement box type muffler, only with thicker metal and more baffles. I'd still have the issue of the hot gas exiting directly at the deck control levers. Though maybe the exit pipe will be more tolerant of a bend as the gas speed will be lower? A lot of the US forum pictures I've seen just have a 1/2" 90 degree iron pipe fitting screwed into the engine, and a silencer (either perforated pipe with glass packing, or an off the shelf cylindrical one) attached to that.

 

[jimmyspeed]

theres nothing wrong with a 90 degree bend. As long as you uses a quality mandrel or something like steam pipe, which keeps a fairly uniform diameter throughout the bend. A mixture of baffles and packed silencers is what most cars uses , from what i remember the baffles are used to cut out the resonance.

 

[rich r]

I'm hoping there's a lot of similarity between a 190cc 6.5hp 4-stroke single cylinder mower engine and a small motorbike/quad bike engine in terms of exhaust gas flow characteristics. Obviously mower engines themselves are pretty mechanically noisy things, but I'm just aiming to maybe soften the exhaust sound a bit by slowing the gas down and blending the pulses a bit. So perhaps I really just need an expansion box to allow the gas to expand and slow down.

I'm tempted to just spend £20 or so on a second hand quad bike exhaust, then chop and weld it so I can attach it to the engine and see what happens.

 

[Paul99]

Didn't mean to imply that a 90 degree bend was no good at all - only that a sharp 45 degree mitred + welded section of pipe isn't a good idea - even 90 degree pipe elbows have a bit of a radius so would be fine and one made with a pipe bender even better I suppose.

 

[pedrobedro]

Just put a louvre over the exit hole to deflect the exhaust gases to where you want them.

 

[rich r]

Sadly the mower is effectively a flat sheet of metal (it's an MTD Pinto), with the engine in the middle and the seat on top. So the exhaust exit is a good 9" from the edge, and the deck and gearbox levers are in that 9" - hence I'm thinking a silencer with a proper tailpipe will be the only way to get the exhaust to exit behind the levers.

I'll go with a nice rounded bend (1/2" gas pipe fitting maybe?) where the original muffler box is, then see what I can get to fit in terms of silencer on the end of that.

Nobody's said it's a silly idea though, so I think I'll give it a go