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Old 05-12-2010, 10:04 PM   #1
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Propane Mower Conversion


Hello all! I'm pretty new to this forum, and I've enjoyed reading about all your ideas and learning from your advice. I share your enthusiasm for DIY projects to save money, time, and energy by making things more efficient, cleaner, faster, nicer, and more enjoyable.

I wanted to share a neat mower project of mine. read about some propane mowers that have started to hit the market, but they are pretty expensive.

So, I decided to take it upon myself to make a "poor man's" green mower for less than $60 bucks.

Stage 1: Get the mower running on propane
I bought a used briggs & stratton 3.5 HP basic push mower from the pawn shop for $40 bucks. This model is easy to convert to propane because it has a place on the intake you can hook up a hose to. No drilling, no carb mods.
To convert it to propane, I bought a blow torch kit ($10 with bottle), black plastic tubing ($2.50), 2 large hose clamps ($1.00), 2 small hose clamps ($1.00 and some zip ties ($0.50). I cut off the end of the torch nozzle so the propane could flow freely and I could connect a hose to it. All that was left was a nozzle and a pipe end. I connected the hose to the nozzle and ran it up and around, following some of the other cables to the engine. I disconnected the PCV hose from the factory nipple in the carb venturi and connected the propane hose to it. I then ran the PCV hose up through the air filter. This is a dual fuel setup, keeping the rest of the fuel system intact. (NOTE: The tube coming through the air filter is NOT propane, it's for the PCV. The propane hose connects to where the PCV hose used to connect on the side of the carb)

Before I tried running it on propane, I tried to start it using the gas that was left in the tank from the pawn shop. Ironically, I couldn't get it to start on the gas and ended up flooding the engine. Go figure.

So, I drained the tank and cranked up the propane. It started on the first pull and ran great. I then mowed the lawn.

I can get about 2-3 hours runtime from a single blow torch propane cylinder that costs $2.85 from Home Depot. I can mow the lawn about 4 times with 1 cylinder. I get more runtime with hotter weather because of the increased bottle pressure. If you really want to save money, get a refill adapter and refill the small cylinder from a 10LB tank.

Stage II: Mods!!!!
The mower ran great in its current configuration, but I couldn't leave it as is. It was begging me to mod it. Since propane has less energy than gasoline, there were a few things I could do to make it a bit more efficient and make more power, mainly increase the ignition timing and bump the compression.

The briggs motors on the lawnmowers are the same engine that they use in the racing go karts, so there were lots of parts to choose from, plus tons of techniques to make more power. Here's what I did:

1. Flywheel offset key to increase ignition timing 9 degrees BTDC.
2. Shave head on belt sander .025" and remove .065" head gasket. I used exhaust paste to seal the head to the block. By removing .090" from the combustion chamber, I must have increased compression by at least a few points.
3. Grade "V" head bolts
4. e3 diamondfire spark plug
5. Royal Purple 10W30 Synthetic Racing Oil
6. Drilled a few small holes in the muffler to increase flow without making it too loud.
7. 21" "GatorBlade"

It really liked the bump in compression and ignition timing.

It's not as "green" as an electric mower powered by solar panels, but it has less emissions than running gas. With propane, it never fouls plugs, and the oil never gets dirty. With a summer or two of mowing the lawn, I'll save enough in gas, oil and spark plugs by using propane that I'll pay for the mower and the conversion.

Let me know what you all think!

Homer
Attached Thumbnails
Propane Mower Conversion-1.jpg   Propane Mower Conversion-2.jpg   Propane Mower Conversion-3.jpg   Propane Mower Conversion-4.jpg   Propane Mower Conversion-5.jpg  



Last edited by homerb; 05-12-2010 at 10:11 PM.
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Old 05-13-2010, 10:08 AM   #2
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Propane Mower Conversion


gotta love inventive ingenuity

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Old 05-13-2010, 10:53 AM   #3
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Propane Mower Conversion


The coolest part is that the blue propane bottle looks like a NOS nitrous tank. VROOOOOMMM!!!

I get crazier looks from my neighbors when I mow my lawn than Rick Moranis gets on "Honey I Shrunk the Kid" with all his gadgets..

I was thinking of mounting a second tank on the other side and tapping it in using a T-fitting. When using one bottle, it gets cold after about 10 minutes of mowing which reduces the bottle pressure. When I'm nearing 1/4 full on a tank when it's cold, often it won't supply enough pressure to keep the engine running. I'll have to switch to another tank (often another partially full tank from the last time I mowed the lawn) or soak it in a tub of hot water. Two tanks would eliminate this problem because I could switch over, or just run both half as much.

Homer
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Old 05-13-2010, 11:51 AM   #4
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Propane Mower Conversion


Green mower

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Old 05-14-2010, 09:24 AM   #5
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Propane Mower Conversion


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Green mower

I guess you can't get any greener than that! Zero emissions and simple. "Classic". How much do those cost?

This is a green forum, but most importantly, it's a "DIY" forum. And a propane mower is a great example of green DIY tech that actually works.
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Old 05-14-2010, 10:05 AM   #6
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Propane Mower Conversion


They can actually be expensive, up to $200
But a small 14" can be as low as $79, 20" @ $140--prices have come down
They sell out pretty quickly too, MIL had a hard time finding one
I would consider one once all of my gardens are in & the new driveway

My lot is 1/2 acre, but between pool area, woods, stream, house, sons play area, greenhouse & gardens there isn't a lot of grass left
I can mow the whole thing in about an hour now

And if you really want a work out on a bigger yard:


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Old 05-14-2010, 10:32 AM   #7
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Propane Mower Conversion


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Originally Posted by Scuba_Dave View Post
They can actually be expensive, up to $200
But a small 14" can be as low as $79, 20" @ $140--prices have come down
They sell out pretty quickly too, MIL had a hard time finding one
I would consider one once all of my gardens are in & the new driveway

My lot is 1/2 acre, but between pool area, woods, stream, house, sons play area, greenhouse & gardens there isn't a lot of grass left
I can mow the whole thing in about an hour now

And if you really want a work out on a bigger yard:


Haha that looks like something you'd tow behind a mule. Free lawn fertilizer too!

Here's a video of it running on the propane bottle

Viddler.com - Souped up lawn mower running on propane (1 of 2) - Uploaded by homerberkowitz

Here's a video of it running on MAPP gas!!!

Viddler.com - Souped up lawnmower running on MAPP gas (2 of 2) - Uploaded by homerberkowitz

Let me know what you think!
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Old 05-15-2010, 12:24 PM   #8
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Propane Mower Conversion


Haha that is awesome! With all that power I hope it's a mulcher at least lol.
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Old 05-15-2010, 04:44 PM   #9
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Propane Mower Conversion


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Haha that is awesome! With all that power I hope it's a mulcher at least lol.
It does a pretty good job mulching. I added a 21" "Gator Blade" that has mulching "tines" at the top of the blade. It's only a 20" mower, so I had to do a little "massaging" to the mower deck to get it to fit.



It does a good job chewing up pretty much everything I throw at it. The only problem with this blade is that it spits out lots of debris, dust, clippings etc. out of all sides of the mower, especially out the front. It makes a big mess of itself. I was thinking of attaching some flexible plastic around the sides.

I was half tempted to close up the mower chute too.

Last edited by homerb; 05-15-2010 at 04:46 PM.
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Old 05-16-2010, 07:17 PM   #10
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Propane Mower Conversion


I converted my Snapper mower to propane in Spring of '09 and used it all summer. My first conversion was just like Homerb's, except that I removed the carb and installed a home-made mixer
Like Homerb's, after about 10 minutes (give-or-take depending on ambient-temperature) the tank and torch-valve frosted up-- reducing the vaporization to the point where I had to take a break. I too had the idea to use a second tank and a T-fitting. I ending up upgrading to a new setup about a month later, which included two regulators. The first regulator takes tank pressure and reduces it to about 1/2 psi. The low-pressure vaporous propane is then fed to a secondary (demand) regulator. I purchase the demand regulator with a bunch of other propane parts on ebay with the intent to convert an antique car to run propane. For more information, please check out my website:
http://www.aircooledpropane.com/
http://www.AirCooledPropane.com/mower/rev2.htm

With the regulators installed, The mower runs until the tank is completely empty, and then dies really quick. You can buy the primary regulator at Menards for between $10 and $15; WELL-WORTH THE MONEY!!

I recently upgraded to a 5-lb tank which can be refilled for about $6.50 at my local Ace hardware. That amount of propane should last me most of the mowing season, I think. Here's a link to the upgrade:
http://www.aircooledpropane.com/mower/rev3.htm

I plan to install that 5-lb tank on a different mower, since it may interfere with the bag on the Snapper.
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Old 05-27-2010, 09:55 PM   #11
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Propane Mower Conversion


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Originally Posted by AirCooledPropan View Post
I converted my Snapper mower to propane in Spring of '09 and used it all summer. My first conversion was just like Homerb's, except that I removed the carb and installed a home-made mixer
Like Homerb's, after about 10 minutes (give-or-take depending on ambient-temperature) the tank and torch-valve frosted up-- reducing the vaporization to the point where I had to take a break. I too had the idea to use a second tank and a T-fitting. I ending up upgrading to a new setup about a month later, which included two regulators. The first regulator takes tank pressure and reduces it to about 1/2 psi. The low-pressure vaporous propane is then fed to a secondary (demand) regulator. I purchase the demand regulator with a bunch of other propane parts on ebay with the intent to convert an antique car to run propane. For more information, please check out my website:
http://www.aircooledpropane.com/
http://www.AirCooledPropane.com/mower/rev2.htm

With the regulators installed, The mower runs until the tank is completely empty, and then dies really quick. You can buy the primary regulator at Menards for between $10 and $15; WELL-WORTH THE MONEY!!

I recently upgraded to a 5-lb tank which can be refilled for about $6.50 at my local Ace hardware. That amount of propane should last me most of the mowing season, I think. Here's a link to the upgrade:
http://www.aircooledpropane.com/mower/rev3.htm

I plan to install that 5-lb tank on a different mower, since it may interfere with the bag on the Snapper.
That's cool! Thanks for the info!

You'll need a regulator with anything bigger than a torch propane tank, correct? The reason why it runs all the way until empty is because the 5LB tank has a tube that goes to the bottom and since liquid propane comes out instead of gas, it isn't affected by the bottle pressure.

I've seen some cool regulators designed specifically for this purpose. They are controlled by engine vacuum or spring pressure, regulating the amount of propane to keep the engine at a specific RPM based on not only vacuum, engine load, but also bottle pressure.

If I were to convert my generator to propane, I'd need some sort of regulator like this so I wouldn't have to constantly adjust the valve to keep the engine running at a specific rpm
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Old 05-28-2010, 12:15 AM   #12
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Propane Mower Conversion


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Originally Posted by homerb View Post
That's cool! Thanks for the info!

You'll need a regulator with anything bigger than a torch propane tank, correct? The reason why it runs all the way until empty is because the 5LB tank has a tube that goes to the bottom and since liquid propane comes out instead of gas, it isn't affected by the bottle pressure.
Thanks. I ran the first conversion off of a 1lb (coleman style) bottle for all summer last year. I use a regulator that screws right onto the bottle and takes tank pressure down to about 1/2 psi. the hose from that regulator is connected to a secondary regulator (a demand-regulator) which is a Garretson SD model. With the governor still working, the engine's load affects the throttle which alters the vacuum to the demand regulator or zero-governor, adjusting the amount of propane delivered to the mixer. A small ball valve (1/4") is used to adjust the mixture, which is mounted as close to the mixer as possible.

http://www.aircooledpropane.com/mower/rev2.htm

Sorry, but I forgot to mention this:

I am using vapor-withdrawal from the tank on both conversions. Once I began using a regulator to reduce the pressure, the tank no longer iced up, allowing it to deliver a fairly consistent vapor-pressure.
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Old 05-28-2010, 01:02 AM   #13
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Propane Mower Conversion


pretty slick stuff guys.

Now all I have to do is have a need for a mower and I could whip one up as well. 2 acres but no grass to mow. I feel left out.
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Old 06-01-2010, 04:08 PM   #14
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Propane Mower Conversion


I have recently worked up a set of plans for this. Mine involve a demand regulator and spud-in, so you can use them on engines with float-bowl carbs. Also, no problems with the bottle icing up, etc.

I'm just working the final kinks out of the plan set but it can be done for about $120-140 and will work just like your regular mower. The demand regulator may also slightly increase run-time per bottle as it's only pulling what it needs to run.
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Old 08-31-2010, 05:44 PM   #15
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Propane Mower Conversion


An on demand regulator is the one part I didn't use on this project. Being that I only paid $40 for the mower itself, I wanted to keep it as low budget as possible.

I can extend the runtime on the mower by simply throttling it down a bit. The rpm and mixture auto adjust based on how much propane goes into the mower.

I am interested in using an on demand regulator for my next project, which will need it. I have a generac 7500 w / 13,500 w peak generator that can power my whole house. I haven't converted it to propane yet because I need that on demand regulator. With the mower, I can constantly adjust the propane flow as needed, but the generator needs to be much more reliable, and it needs to auto adjust the flow based on how much stuff I have running in the house.

I haven't even needed to use the generator once since I bought it from the pawn shop for $275, so I don't even know how much gas it uses per hour. But propane is a much better choice because it stores better, doesn't foul plugs, gum up the carb, and extends oil change intervals. Im guessing it'll run for about 4 hours on a typical 20lb tank at half load. Im hoping it'll run longer, if it is to be cost effective though. I could get one of those big 100lb tanks and have it run all day without changing a tank.

What kind of on demand regulator are you planning to use? I've been looking on eBay lately and there are a few different kinds on there.

Homer

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