Building an Otto-Langen Atmospheric Engine -With a Little Help from the Curbside Parts Supply

Rotisserie motor

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I had just finished my 'VBS Engine' (see GEM, June 2001) and was looking for another engine project, but it had to be an unusual engine. The Otto-Langen atmospheric engine of 1864 had always interested me, but I had never seen one.

Wayne Grenning's Web site (http://members., had a revised edition of his February 1991 Gas Engine Magazine article, which was my main source of information on this early engine.

The Otto-Langen engine was the first internal combustion engine to go into production, and from 1864 to 1876 about 4,000 engines were built using a free piston design. The power of these early giants was low and the engines were big: A 2 HP engine weighed about two tons. Low horsepower seemed great for a home-built engine, so I put Nicolaus Otto's design on a diet and introduce some new engine components.

My home-built engine wasn't going to be a scale model (Wayne Grenning already offers excellent Otto-Langen models), just a home-built engine put together with junk. I didn't bother to make formal drawings or even a sketch, as that might have restricted me since my intention was to use available parts and materials in building this engine. The only power tools used on this project were a drill press, belt sander and 3/8-inch electric drill. Mo welding, lathe turning or milling was required.

Sourcing Parts

The engine is mounted to a discarded lawn mower frame turned upside down.

My first stop for parts was R&S Performance in Orlando, Fla. Scooter and Big Daddy, the moving forces behind R&S, make a living by repairing and maintaining air-cooled Volkswagens (VW) but live to build and drag-race Volkswagen-powered cars. My initial shopping list was a later model VW, 1,600 cc dual-port head and cylinder, which were easy to find in their scrap pile. I cut the head in half, modified the valve spring retainers to operate with very weak springs and made a progressive rocker arm assembly, using two door hinges to sequentially open the valves using one push rod (actually, my inverted engine uses a 'pull rod,' not a push rod). A small piece of foam rubber saturated with oil and wrapped around the valve stems provides lubrication. I wasn't sure how big the combustion chamber should be for this low-efficiency engine, so I extended the 85.5 mm cylinder with a 90.5 mm cylinder. I drove the two cylinders together, skirt-to-skirt (a VW cylinder has a protruding skirt that mates to the engine case), and sealed the surface between the two cylinders with a copper head gasket and flat gasket material cemented between the two cylinders. I was beginning to realize that each step of this home-built engine would be a 'science project,' and workable solutions would have to be determined before proceeding to the next issue.

A scrap VW bus brake drum was selected to terminate the combustion chamber and translate it to a 1-1/4-inch pipe fitting. The outside face of the VW brake drum is turned flat, providing an easy seal for the 90.5 mm cylinder to brake drum interface. There are holes drilled through the brake drum, and threaded rod running through the VW head, the two cylinders and the brake drum bolts them all together.

As this engine was going to be big, some type of frame was going to be necessary to mount up this odd accumulation of junk. An original 2 HP Otto-Langen was about 10 feet high, and just the head and combustion chamber on my home-built engine was 20 inches tall. The 'Curbside Parts Supply' (trash piles) had a nice chrome-plated clothing display rack that 1 used for part of the engine frame. Some steel angle iron salvaged from old bed frames made for a sturdy fixture between the brake drum and the clothing frame, with holes drilled in the brake drum securing it to the angle iron. The VW cylinders and head are suspended from the brake drum.

My initial idea for a carburetor was to bubble air through a glass jar filled with gasoline, but the more I thought about this idea the more I wanted to incorporate safety features to prevent any possible fire or explosion. Scooter suggested using a fuel injector, and at first I thought this sounded too high tech. I took his advice, however, especially since he also offered an intake manifold with injectors from a Type Ill Volkswagen. The fuel injector would require pressurized gasoline, so I converted a compressed air dryer housing into a pressurized fuel tank. My engine has no intake stroke to suck the gas and air mixture into the cylinder, so I mounted a small blower on the intake manifold. Talk about high tech, this 1864 design was now becoming a supercharged, fuel-injected beast. The 'blower,' by the way, is a 12-volt raft inflator, and at $5.49 the single most expensive part I bought for this engine.

Slow-running engines attract attention at engine shows, and I decided that firing the engine every 12 seconds was a good starting point for a slow engine. The 'Curbside Parts Supply' provided a 5 rpm rotisserie motor from an outdoor grill. I mounted the rotisserie motor to the clothing rack engine frame, and on the motor's armature I mounted an arm to be connected to the valve lifters. Also, mounted to the armature is a round aluminum disk with a scrap of Formica bonded on one side. This functions as a rotating electrical contact to turn on the blower, fuel injector and ignition system at the correct time, with three sets of electrical wipers contacting bare wires that are mounted through the Formica and grounded to the aluminum disk. I drilled extra holes in the timing wheel so I can change the timing of these three electrical functions by moving the grounded jumper wire locations.

'I still hadn 't worked out the details for my cylinder and piston, but I needed to see some action just to keep my interest in this never-ending engine project.'

The basic design of this free piston engine is 138 years old, but up to this point I hadn't used any parts that were over 30 years old. Old engine people like to see some old parts used, and since I wouldn't want to disappoint anyone I fitted a Ford Model T ignition coil to fire the spark plug.

I still hadn't worked out the details for my cylinder and piston, but I needed to see some action just to keep my interest in this never-ending engine project. I took some scrap 1-1/4-inch PVC pipe and used it for a temporary test-cylinder because it is easy to work with. I put gasoline in the pressurized tank, and using an old computer power supply I sent 120 volts AC to the rotisserie motor. I then turned everything on, but nothing happened. Twelve seconds later the engine was ready to fire again, and just as the Ford coil buzzed I heard a muffled 'WHOMP', like you'd hear lighting a gas stove. I wadded up a 'shop rag' and jammed it in the open 1-1/4-inch PVC cylinder just in time for the next firing sequence. BANG! My shop rag blew about 20 feet in the air and was hanging on a limb in my oak tree. I stuffed another rag. BANG! Another shop rag was hanging in the tree. I quickly disconnected the power and begin to look for a long pole to get my shop rags down from the oak tree. I live in a city with neighbors all around, and my 'shop rags' are old underwear. It's one thing to have the neighbors talking about my strange engines, but underwear still smoking and hanging in the trees may create more attention than I want.

My next test was to see if the engine had enough power to turn a flywheel. A piece of 3/4-inch PCV pipe was weighted and vented with an old valve and rigged up as a piston. The vented 'test piston' cleared the PVC cylinder by about 2 feet with its vent wide open. I never bothered to completely close the vent for fear of taking down small airplanes that frequent a nearby airport. I took the engine apart and drilled and tapped holes in the brake drum and added copper tubing to vent some of the power from the combustion chamber. One of these vent lines is tied directly to the exhaust system, and the other goes through a gate valve and then to the exhaust system. Adjusting this valve or varying the pressure in the fuel tank allows me to have some control of the power output.

This home-built engine would have to fit in the trunk of my Honda Civic, so I made the flywheel support a bolt-on arrangement made from a couple of front bicycle forks, some plumbing fittings and more bed frame angle iron. Loosening some bolts and sliding the pieces into their proper position allows the flywheel and piston to be aligned. I had originally planned to use a heavy flywheel about 15 inches in diameter, but I changed my design to save weight and ease the assembly process. This upper engine subassembly is secured to the clothing rack with eight bolts, and after initial setup it requires very little alignment when reassembling.

The connecting rod in the Otto-Langen engine did not pivot on a wrist pin but was instead rigidly connected to the piston with a rack gear mounted on one edge of the connecting rod. I had several ideas on how to do this but settled on a simple idea that relies on a material that is, pound for pound, stronger than steel: wood! Nothing fancy, just an old rake handle secured with epoxy in a piece of thin-wall PVC pipe and with holes drilled every 1/2-inch to engage a bicycle sprocket. The PVC pipe provides a uniform surface for laying out the holes to be drilled for the sprocket, and it also permits an easy translation to 3/4-inch iron pipe fittings that can take the high temperature of the combustion chamber during the ignition/combustion (upward piston stroke) cycle. Elastic shock cord limits the stroke and helps accelerate my lightweight piston on its downward (power) stroke.

Ten-speed bicycles use a roller clutch that is similar in function to the one originally designed for the Otto-Langen engine. And since a bicycle wheel is, in fact, similar to a flywheel, why reinvent clutches and flywheels when the 'Curbside Parts Supply' always has the best prices in town? I found an 18-speed bicycle that probably was run over by a car, and after a lot or work I got the rear wheel straight enough to use. It still has some wobble, which I like to refer to as character.

'It's one thing to have the neighbors talking about my strange engines, but underwear still smoking and hanging in the trees may create more attention than I want.'

A local bike shop loaned me the special wrench to dissemble the free-wheel sprocket cluster, which I then reassembled with two 26-tooth sprockets and one 16-tooth sprocket. The 26-tooth sprockets restrict the connecting rod and center it so the 16-tooth sprocket situated between the two will engage in the holes I drilled in the connecting rod.

A length of bicycle chain secured to the rim of the bicycle wheel gives it some mass, increasing its turning time by 20 percent. The bicycle wheel flywheel seemed to work so well I started to consider keeping the PVC cylinder and increasing the time between ignitions to reduce heat output, perhaps enough to allow the engine to survive short demonstration runs. I knew the reduced power would produce a slower running engine, but who needs power? The wooden connecting rod and PVC cylinder became a permanent part of this unique, slow running engine, eliminating the need for any welding and machining on this project.

I initially used a 120-volt AC rotisserie motor and a power supply from a trashed computer for an external power source, but now that the engine was showing some promise of actually working I started converting everything to 12-volt battery power. I had considered a DC/AC converter to run the rotisserie motor, but 1 found a battery-powered rotisserie motor at the 'Curbside Parts Supply.' This should have been an easy and quick motor replacement, but the process of incorporating ball bearings and an improved timing wheel mount turned this phase into still another never-ending 'science project.' After salvaging another trashed computer I came up with enough parts to make an adjustable voltage regulator for the rotisserie motor so I could provide uniformed timing for the air, fuel and ignition systems. More salvaged components went into another voltage regulator to power up the raft inflator, or 'supercharger.' I felt a good evacuation and charging of the combustion chamber could be accomplished at a lower fan speed, which should increase the life of this motor, my most expensive single part ($5.49). Regulating the voltage to the rotisserie motor to three volts and the 'supercharger' to five volts should make these components perform uniformly regardless of the voltage of my 12-volt battery.

To control the timing wheel I picked out a motion detector security light with some problems (small fire) in its power supply but with all its other functions working okay. I used duct tape (almost everything I build uses some duct tape somewhere) to 'blind' the day/night sensor. I replaced the relay so the motion detector now turns power to the rotisserie motor off rather than turning a security light on. A small light bulb wired in parallel with the Ford buzz coil is mounted in front of the motion sensor. When power is applied to the Ford coil the spark plug fires and the light flashes on, which triggers the motion detector to turn the power to the rotisserie motor off. I relocated the adjustable time-delay resistor to the control panel where I can change the time between engine firings by turning a knob.

Making it Portable

The clothing rack engine frame had four legs extending out to stabilize the rack, but this prevented the engine from fitting in my Honda Civic. I built a full size mock-up out of wood and cardboard so I could try every possible way to get the engine in the car: The mock-up would just barely fit with its legs cut off. I then added weight to the mock-up to make sure I could get it in out of the trunk by myself. Cutting the legs off the engine made it unstable, and 1 needed wheels to make it mobile around the shop. To get around this I mounted the engine to an old lawn mower deck turned upside down. Bed frame angle iron and clamps secure the engine to the mower deck, and the wheels are adjusted to give the deck about a 1/2-inch of ground clearance. With this 'low-boy' cart I can wheel the engine into my garage (after slipping off the shock cord over-travel assembly) with a 1/4-inch of clearance. I added leveling screws to the lawn mower deck to adjust for the uneven ground locations often encountered at engine shows.

How it Works

The sequence of events on this engine can be divided into two major categories: When the timing wheel (rotisserie motor) is turning and when the time-delay circuit is active (and the timing wheel is not turning). The timing wheel turns for 12 seconds, during which the following events take place: Timing wheel starts to turn, intake valve starts to open, exhaust valve starts to open, blower starts, exhaust valve starts to close, fuel injector fires, exhaust valve closed, intake valve closed, blower stops, ignition and the timing wheel stops and waits for the electronic (adjustable) time delay to start the sequence again. The electronic time delay is adjusted to fire the engine every two minutes, which keeps the flywheel in continuous motion and allows the PVC cylinder to cool down so the engine can run all day with a nominal power stroke of 30 inches. When I first got this engine running I was using regular gasoline, but since this engine uses so little gas I switched to lantern fuel as it doesn't go bad if left in the tank. Fuel consumption is low: Four ounces of camp lantern fuel is all I need for eight to 10 hours of continuous running at shows.

'The Otto-Volks Engine' is the name I gave this home-built engine because it is based on Nicolaus Otto's design and it uses a lot of VW parts. My engine club, The Florida Flywheelers, was the first group to see The Otto-Volks engine running and it attracted attention all day long at their shows. This whimsical contraption at first glance appears to be just another attention-getting gadget, but further observation shows this non-compressing, free-piston engine design with roller clutch uses several principles introduced by the 1864 Otto-Langen atmospheric engine. The materials used in my home-built engine are easy to obtain and can be modified with simple tools. This makes it a good engine to build if you do not have access to a machine shop or welding equipment.

Watching the expression on people's faces when they recognize familiar parts (such as bicycle, VW or lawn mower parts) that I have used on my engine is priceless. Especially rewarding is the reaction from young people when they realize that you can use parts for purposes other than that for which they were originally intended. These young minds will soon be in control of our hobby and our nation, and if we do not expose them to how things were done in the past, and how to improvise, how can we expect them to make good decisions in the future?

Contact engine enthusiast George Fair at: 118 N. Glenwood Ave., Orlando FL 32803, (407) 894-8796, or e-mail: