Convert a Lawn Mower Engine to Steam or Air




About: bored kid

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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    23 Discussions


    2 years ago

    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


    7 years ago on Step 9

    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.

    11 replies

    Reply 7 years ago on Introduction

    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


    Reply 7 years ago on Introduction

    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.


    Reply 3 years ago

    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


    Reply 4 years ago on Introduction

    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.


    Reply 6 years ago on Introduction

    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.


    Reply 6 years ago on Introduction

    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.


    Reply 7 years ago on Step 9

    My first thought is avoid. Want a challenge, try to build an electric, or veggie diesel. Make it a hybrid gas turbine/electric But as much as I like steam engines, a large, prototype steam vehicle is no place for an amateur. You don't want to play with a steam plant powerful enough to move a motor home. Do not meddle in the affairs of dragons, as you are crunchy, and taste good with ketchup.

    If you are going to convert something, in its favor, a motor home is large enough that you should be able to find a place to put a boiler. (it definitely won't fit where the original engine lived, expect it to be bigger than a household double door refrigerator). Given that they use a truck chassis, it should be able to take the extra weight of the boiler and the water storage system, assuming the motor home builder didn't go overboard on the decor (no granite counter tops, or marble floors....).

    The conversion will be "straightforward" (as anything involving superheated steam can be called straightforward) . you will find the process of inspection and getting the required permits to be the difficult part.. (the boiler inspection is national, but the operator licensing is by state, and not all have reciprocal arrangements) A boiler large enough to move a motor home, is definitely large enough to interest the regulators.

    The hard part of any steam power system is the boiler. The engine is essentially an afterthought. And since they can explode (even the low pressure ones), and a simple pinhole leak in 600 psi steam plumbing (what the Stanley's ran) can kill, boilers are responsible for the very idea/existence of industrial safety laws.

    Go visit a power plant, or other facility where they are running steam at 50 bar or higher. Ask someone on the maintenance crew to show you the leak detection tool. They will point to a 10' hunk of 2x4. To use, hold it out in front of you sweeping it up and down. When the far end of the plank explodes into a bunch of splinters, you found the leak. When it catches fire, you are real close. At those pressures you won't see the steam escaping at the hole. you don't get the white cloud until a few feet away from the leak, when it will have cooled enough to condense.

    I encourage people to play around with model steam. If you want to try something significantly bigger (able to power a couple of houses), or running at noticeable pressure (over 200 psi) , a stationary system with some provision to keep the shrapnel inside your property line is tolerable, (put it below grade say) You can do a boat if you keep the size reasonable and your pressure under 10 bar. (your classic 20 foot steam launch with a 2-3hp engine and the all important fringed fabric roof)

    If you aren't already an ASME member and certified welder, (and already own and have read a copy of the applicable standards) don't try to design or build your own over-the-road system, especially if you want it to go highway speeds. and on public roads. You may be fine with the risk, but the guy in the next lane didn't agree.


    Reply 7 years ago on Step 9

    thanks for the honest and informed answer, I'll keep refining my ideas have you read anything on superheated steam on the fly?


    3 years ago

    How about corrosion in this thing? Seriously want to build this but i am afraid corrosion would make the engine stop rather quickly.


    4 years ago on Introduction

    Why is steam still a viable approach? We have two Australians not of Australian blood mind you that have revolutionized compressed air motors. You guys may have heard of the first one Guy Negre a former Formula 1 engineer he currently has a range of 200km on a single compressed air tank made or kevlar for safety purposes. The other Angelo Di Pietro has made a rotary motor that runs on compressed air. I have always disliked reciprocating piston motors they are so inefficient. Mass that is thrown stopped and thrown once again is an obvious loss and inefficient and requires other mechanics/complexities for it to run "efficiently".

    Please read Di Pietro's take on the rotary it really is ingenious. I just wish that someone other than Mazda, say Toyota, would pick up the torch and really bring the rotary to the main stream after solving it's few faults/cons.


    4 years ago on Step 9

    Yes it will be a greatly modified amount of power but remember that a boiler running at a head of steam of as little as 50 lbs is a dangerous instrument. Unlicensed boilers in industrial applications are only allowed 15 lbs of steam. After that a Steam Engineer of at least third class must be employed to operate to 120 lbs of steam. Second Class can go to 180 lbs and only a first class steam engineer can go beyond that. So long as you operate it solely for your own use you can be reasonably safe operating at up to 50 lbs. At this pressure you could have the engine operate a boat or a small generator but not much else. Don't try to run a traction engine because there is just not enough power there. Do not display it running at a public event. You need to have some sort of Steam Certification for that.


    4 years ago on Introduction

    isn't it easier to modify the exhaust port to open when the piston is at tdc and run the engine like a gas engine


    4 years ago on Introduction

    hi guys, good to see some interest in steam engines, i am a retired small engines mechanic and have noted a small but critical error, that can easily be fixed, the camshaft to crankshaft gear ratios are incorrect and need to be a 1-1 ratio, unmodified, there would be a large energy loss, ie, induction-compression-power-exaust.

    we need to convert it to a 2 stroke engine,,, to do this, it would be best to remove the cam,its related pins and that little plastic thing which is a governor, but leave the valves and springs in position, cutting through a fin or two and boring an exauste port at the bottom of the cylinder just above the piston at bdc {bottom dead centre}will give a piston governed valveless exauste port, which works the same as the scavenger port on a 2 stroke engine, {an even better idea would be to cut a slot at that point rather than a hole, its easier done} we then use the spark plug hole as the steam input, now here comes the good part, being that it is a steam engine we are making and that the flywheel of the four stroke has imbedded magnets we can now mount some sort of induction coil making a switch mechanism, to control the input of the external steam valve or gate, in other words using this magnetic influence to control a solanoid valve, incorperated with an advance - delay function therefore advancing or retarding the timing, therefore giving maximum power output at both low and high revolutions. i do not believe that achieving this would be all that complicated , or expensive,given the electronics available today,

    i hope you guys have found this to be informative, and best of luck, i am going to have a go at this myself,


    5 years ago on Introduction

    Spenceravery says:
    I have an answer hopefully to what you are asking, use JB KWIK!! check it out!! I have an engine that has a nylon camshaft, so I made the opposite cam out of JB KWIK!!
    Just checkout JB KWIK!! Its pretty good stuff!! It is a goopy metal like two part epoxy that
    dries rock hard like metal!! You can shape it sand it , drill it!!


    6 years ago on Introduction

    hey everyone, what do you do if you have a lawn mower that has a nylon cam shaft ? i have managed to get the opposite side to the main lobes and welded a piece of steel to get the correct timing for the valves dose anyone else know how i could do it ? i am really looking forward to getting it running because it is a great project i have recently taken a large interest in steam/air powered engines