Convert a Lawn Mower Engine to Steam or Air





Introduction: Convert a Lawn Mower Engine to Steam or Air

This is an instructable on how to change the camshaft timing so that you can run a push mower engine on steam/compressed air you can usually pick up these engines really cheap or free

I am entering this instructable in the hack it! challenge  and the mad science fair so so would love the vote's if you like it

Step 1: Tools

wrench or socket set 
screw driver set
welder ( if you give the camshaft to a friend with a welder or someone who takes shop in school they should be able to do it with ease)
hammer (optional helps with stubborn things that get stuck)

Step 2: Strip the Engine

first strip the engine of all unneeded parts such as the carborator the muffler magneto etc. you need the spark plug left in. 

Step 3: Draining Oil

first you need to drain all of the oil out of the crankcase.

Step 4: Crankcase Cover

now that the oil is drained its time to take the cover off

Step 5: Camshaft Removal

now that you have the cover off you should see the inside of your engines crankcase look for the big gear off of the shaft

Step 6: Modifying the Camshaft

now that you have removed the camshaft you need to modify it so that it will run on compressed air or steam do do this you need to modify the timing lobes the lobes on the gas engine allow the engine a intake compression and exhaust cycle what you want to do is to modify the timing so that it only has a power and exhaust stroke look at the existing lobe and weld on a lobe to the opposite side then take it to your bench grinder and grind at the weld until it is smooth and looks like the the original side ( do not grind off the original lobe you want both of them) 

Step 7: Testing

for this step you need to remove the engines head so go ahead and do that now that you can see the valves and the piston you can o the testing the testing is done by putting the modified camshaft into the crankcase and turning the engine while looking at the valves and checking to see if the timing is appropriate to the piston movement one valve should open as the piston goes down and the other should open right as the piston goes up (you cannot have both valves open at the same time it will lower the efficiency temendously and the engine will stall

Step 8: Put It Back Together

after you have completed the testing you need to reassemble the engine so put the crankcase back together with the modified camshaft and put the head back on now for testing you want to use commpressed air so either tap the intake or the ehaust ( if you put the air into the exhaust it will run backwards) or you can make a fitting from a peice of metal and a gasket. now put the engine in a vice to hold it and and apply the air (  dont put to much pressure about 30-45psi) now take a scewdriverand turn the fly wheel until the engine starts turning if it stalls then the timing is off and the two valves are open at the same time. so tear it apart and grind some more if it does not stall then you are done!!!!!

Step 9: Going All Out

if you want to go the final step then you can put on a new flywheel and make a boiler and run the engine on steam also if anyone make a buggy or boat would love some pics



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Steambuddy has a good point. Convert to 2 cycle. Ive done it with a weedeater engine using a solenoid valve. It worked well with air but lacked power & consumes a 26gal tank pretty quick. It definitely looked & sounded cool

This sort of mod is fine for demonstrating a conversion, but you can't make much power. If you use any significant air pressure (a requirement for real power), the inlet valve will just lift.

To get power comparable to the engines rated output, you have to use air or steam at pressures comparable to that developed in the cylinder during combustion, or around 4-500 psi for a typical gasoline engine. The valve spring doesn't stand a chance at that kind of pressure.

i was actually thinking about this as i made them and did't think that i would want that much presure the engine as it was was spinning fast enough i have designed a few other conversions using the sparkplug port i dont like the solinoid valve conversions because they where out from all of the presure unless you get a high presure valve

As a demonstration, your system works fine. Run no load, and don't worry If you actually want to make power (your comment about "cart or boat") it won't do.

If you are using the spark plug hole, you can use a simple ball check valve, actuated by a stud fitted to the piston. Piston gets close to TDC, the pin sticks thru the hole, and pushes the ball off its seat, letting air go past. Drill exhaust ports into the cylinder just above BDC, to let the pressure out. (you even get to call it a "uniflow" conversion).

Yes, it does mean that pressure is let in before tdc, so it does mean you need a flywheel, and the engine won't run well at low speeds, (it will be like a split-phase electric motor, lots of power at speed, but lug it a little bit, and it stalls). It won't be self starting (single cylinder engines of any valve configuration rarely are). But with a bit of flywheel to keep it spinning, it will run, (in whichever direction you start it in) and run well.

You can still buy today, very small engines that work just this way, for indoor model airplane use - they run off CO2 cartridges. (I have even seen a cheap plastic one that you pump up with air) They have mostly been replaced by electric motors, but there are still some out there

Oh yea, stick to air to run such things. A steam boiler large enough to get actual power out of such an engine is large enough to interest the people that regulate such things. It means a certified design and construction, regular inspections (there is a national board of boiler inspectors), and in some locales operator licensing. Getting a 5hp boiler wrong, can result in an "energetic" event. The sort of event that leaves a crater and a body count. Just the kind of incident that inspired the relevant laws in the first place.

Also, air won't turn your crankcase full of lubricating oil into something resembling beige mayonnaise, like the steam blowby will. Splash lube doesn't work well if what you are splashing into isn't liquid. If you are going to run the engine for any length of time, be sure to keep it rotating in the same direction it did when running on gas. The connecting rod has a scoop to fling oil where its needed, and it doesn't work if dragged thru backwards.

So im attempting to make a steam powered car using four bikes and a 6hp mower engine what i am not understanding is why cant i just cap the intake is there a pressure problem it causes or something

a ball valve as described would have several problems unfortunately, {1} not enough steam bypassing the valve, {2} the resulting pressure behind the valve will impinge on the face of the piston creating a rather loud knock in your engine,{3} reduced function due to possible imbedding of this control pin in the piston itself{4} total steam control faliure

Hey rjnerd. I am looking to transform a car to run on compressed air but I need to start out small first and work my way up to a car. I have a gas lawn mower that I'm looking to convert but my question is, can you make an Instructable on how to convert a gas engine to run on compressed air? I want some power behind it and you seem to know a lot about this kind of thing.

The simplest conversion is as I mentioned above, a piston actuated check valve, and exhaust ports cut into the cylinder wall. (make life easier still, and start with a two stroke weed wacker, it will have the exhaust ports cut already, and the spark plug will be centered over the piston.

To get any real power, and endurance from an air engine, you have to expand the air in stages. This means a compound engine, just like a steam engine. With a compound engine, you take the exhaust gas (which will still be under some pressure, just not as much as you fed to the first cylinder) and feed it to another cylinder to expand further. To get comparable power from the downstream cylinders, they have to be bigger than the first one. (torque is proportional to piston area x cylinder pressure, decrease one and you have to increase the other)

Now some numbers - say you held the inlet open for 25% of the stroke. It would mean the pressure left in the cylinder when you opened the exhaust valve is 1/4 of what you started with. So to get the same torque from the next stage, you would need a piston with 4 times the area, or double the diameter. Keep the same valve timing, and your third stage would need a piston 4 times the diameter of the first stage...

You will want to do more complicated valve gear, as you will want to vary the "duty cycle" - you can get a lot of power (but poor economy, especially without compounding) by opening the supply valve for most of the stroke. When you open the exhaust valve the cylinder still has a lot of pressure in it. More economical (but lower power) can be had by letting air in for just a short time, and letting it expand for the rest of the stroke. When you open the exhaust valve then, the cylinder will be at lower pressure. The closer your exhaust is to atmospheric pressure, the more work you got out of your air. (any pressure at the exhaust is wasted power). A compound engine lets you take that low pressure air, and make its expansion do real work..

With air, you have another option, you can get direct rotary motors. Many things that can pump air, can also be a motor. If its positive displacement, and valveless, it can be a motor.... Example: Take a typical automotive gear type oil pump. Connect the pickup tube to your air hose. See pump shaft spin. (until lack of lube gets it). As a constant volume device it won't be that efficient, but it will suffice for demo purposes. Purpose built air motors are variable volume designs, to get more energy from the air supply.

So, rjnerd, you seem to know a bit about steam power. what are your thoughts on a coil type flash boiler? I understand they are much safer because of the limited volume of steam.

I think they are great. They do have some control challenges, which are fairly easily solved these days. Coordinating the flame size and water flow, is a pain to do with strictly mechanical bits, but should be trivial for an ardunio. If you cut down the water flow (to throttle down) without adjusting flame quantity, steam temperature can go thru the roof (like 1500F).

This isn't a big deal, as long as your piping system can cope. If you stick to welded or mechanically connected stainless steel plumbing, you won't have a problem. If you do the usual copper and silver soldered connection of hobby steam, it will melt. (and the paint on your steam chest will burn off)

For extra credit go digging thru the patent database. In the 60's a mech e Prof at MIT named Smith (yea, I know there will be too many hits) developed a variant on a flash boiler that added a bunch of packed fine steel balls filling some of the voids between the tubes. Greatly increased the surface area. A prototype built into a 2lb coffee can, got 10hp with natural gas firing. The company formed to commercialize it was called Steam Engine Systems and was in either Watertown, or Newton Mass.