Internal Combustion Engines

Introduction To Gasoline Engine Care and Maintenance


Proper care of a cleaner’s gasoline engine can go a long way to keeping it in continuous operation with minimal downtime. One-or two-cylinder, general purpose internal combustion engines areInflatable fun widely used to power portable high pressure cleaners.

Most of the engines used are gasoline powered but a small percentage of cleaners use diesel engines. Two-cylinder diesel engines are ideally suited for some higher volume and pressure applications. Engine exhaust emissions, including carbon dioxide, make the indoor use of internal combustion engines undesirable except in very well ventilated areas.

Engine Sizes

Standard engine sizes used are 3hp, 5hp, 8hp, 11hp and 18hp. Engines with different horsepower outputs (such as 10hp, 23hp and 25hp) are also available. The 3hp engine usually drives the same pump and produces the same output ranges as a 115 volt elector motor. The 5hp and 8hp engines generally are used in the same applications as 230 volt single-phase electric motors. The 11hp engine may replace a single or three-phase motor and 18hp or larger engines are used in applications where three-phase electric motors would be used.

The Four-Cycle Or Four-Stroke EngineT

Most general purpose engines used to power high pressure cleaning equipment are single or two-cylinder, four-cycle gas engines. In a four-cycle or four stroke engine, each of the four actions occurring in the cylinder takes place during a full stroke of the piston. That is, the piston moves as far as it can in one direction in the cylinder during the intake, compression, expansion and exhaust operations. This means that it requires two full revolutions of the crankshaft for one complete engine power stroke.

Four-cycle engines, unlike the two-cycle engines commonly found on outboard motors and chain saws, do not require addition of oil to the gasoline for lubrication. Oil is placed in an oil reservoir just as is the case with an automobile engine.

Proper Maintenance Is Essential

Lack of proper maintenance is the most common problem with general purpose gasoline engines used to power high pressure cleaners. Often a gas-driven cleaner is operated by several different people, none of whom have clear responsibility for maintaining the engine.

Unlike electric motors, which require little care, a gasoline or diesel engine must be maintained properly to continue to function without problems. Maintenance is directly connected to engine life. Without proper maintenance a gasoline engine may have a service life as short as 400 hours. With proper maintenance this life may be lengthened by a factor of 10 to 4,000 hours. To put this in more familiar terms, consider the engine is driving an automobile at 55 miles per hour. The improperly maintained engine would drive the vehicle 22,000 miles while the properly maintained engine might have a rage of 220,000 miles.

A Sample Gasoline Engine Maintenance Schedule

Engine manufacturers suggest maintenance schedules for each of their products. These maintenance schedules may differ slightly but are similar to the schedule suggested here.

Oil should be checked daily or after five hours of operation, whichever comes first. The air cleaner should be serviced after 25 hours of operation. If the engine is operating in a dusty environment, the filter may need more frequent attention. Regular air cleaner inspection will allow setting a schedule which suits operating conditions specific to a particular engine. Oil should be changed after 25 to 50 hours of operation. This means every one to two weeks if the engine is operated on a fairly continuous basis.

After 100 hours of operation the spark plug gap should be adjusted. The combustion chamber should be cleaned after 100 to 300 hours of service, depending on operating conditions. After 500 to 1000 hours of service, piston rings will probably need replacement. At around the 1000 hour mark an engine overhaul will probably be called for.

Engine Needs

A general purpose gas engine needs several things for long and satisfactory service.

These Include:

Adequate lubrication.

Proper, clean fuel.

Adequate clean air for combustion.

Ignition spark.

Sufficiently cool running conditions.

The absence of any of these conditions will result in engine failure or shortened service life along with costly and unnecessary repairs.

Some Pointers On Proper Lubrication

The oil level should be checked daily. Oil should be changed on a regular schedule. Usually oil should be changed after 50 hours of engine operation if not sooner. An oil change after 25 hours or operation is suggested by some engine manufacturers. Oil is rated with a weight number such as 20 weight, 30 eight or 40 weight. This number indicates the oil’s viscosity or thickness. The higher the number, the thicker the oil. The oil thickness needed generally relates to ambient or air temperature. The cooler the temperature where the engine will be operated, the thinner the oil required.

Multiweight Oils

Multiweight oils which perform will in a range of temperature conditions are available. These will be designated with two numbers such as 10W 40. This means the oil will function as a thinner oil in colder temperatures and a thicker oil in warmer temperatures. When choosing oil, follow the manufacturer’s recommendations.

Whenever oil is added it should be of the same weight and brand used initially. Different brands of oil may have slightly different additives. When oil is changed a different weight or brand may be substituted. Generally, manufacturers recommend SAE 30 weight detergent oil. A detergent oil contains a chemical additive that keeps combustion byproducts emulsified in the oil rather than forming as deposits on engine surfaces. When a detergent oil is used, contaminants such as fuel, soot and other byproducts of combustion drain from the engine when the old oil is drained during the oil change.

Cool Operations

The small, general purpose engine is air cooled. That means heat built up in the engine from combustion is released to the atmosphere. The fins on the outside of the cylinder or cylinders perform like a radiator or heat sink that radiate heat away from the engine. If these fins are dirty, the dirt acts as insulation and heat is retained in the engine. Overheating and engine damage can result. These fins should be cleaned every 50 hours. Most small, air-cooled engines rely on a flywheel-mounted fan to force air around the engine. A shroud around the flywheel directs this airflow around the cooling fins. The engine should not be operated without this shroud in place.

Engine Temperature Limits

Most engines are designed to operate with an external air temperature in the 20 to 100 degree Fahrenheit range. Temperature of gasoline in the fuel tank should not exceed 130 degrees and the oil temperature should remain below 250 degrees. Temperature at the spark plug base gasket should not exceed 500 degrees.

What Overheating Does To The Engine

Higher temperatures can cause vapor lock in the fuel line, abnormally high oil consumption and possible engine damage. Engine overheating can result from a low crankcase oil supply or dirty oil. Use of an inferior grade or oil can cause overheating as well. Use of an inferior grade of fuel or restriction of the exhaust can also cause overheating. Operating the engine at high temperatures can cause the oil to oxidize or break down into carbon and varnish-like substances which can foul moving parts. Good quality oils generally will not break down if the oil is changed on a regular schedule even with high engine temperatures. The varnish-like gum formed by oxidized oil can bake onto engine parts during prolonged operation at high temperatures.

The Right Stuff In The Fuel Tank

Water and debris in the engine fuel tank can degrade engine operation or cause damage. Gasoline blends are changed seasonally, usually four times a year. Fuel blended for winter use is lighter and more volatile to make starting in cold conditions easier. Fuel blended for summer use is heavier and less volatile to prevent “boiling” and engine vapor lock during hot weather. Blends for spring and fall are a compromise between the winter and summer blends. If fuel for a small engine is bought in bulk, a fuel blend intended for use in one set of conditions may carry over into another set of conditions. This can result in poor engine performance.

Fuel Break Down

Fuel can also break down over time. Like oil, fuel can oxidize. Fuel oxidation can cause gum deposits in the carburetor. Fuel gum resulting from gasoline oxidation can be dissolved with acetone. Fuel oxidation can be kept to a minimum by storing fuel in a cool, ventilated place. Fuel in a full tank oxidizes less rapidly since the amount of air which can participate in oxidation is limited.

Air For Combustion

TA gas engine needs about 10,000 gallons of air for every gallon of gasoline consumed. How clean the air is when it gets to the engine’s combustion chamber is a key factor in engine service life. Engines are often used in very dusty or dirty environments so particular attention must be paid to the condition of the engine’s air cleaner.

Air Cleaners

There are two basic types of air cleaners: those with paper elements and those with oiled foam elements. Some engines use both a paper element and an oiled foam element. No matter which type is used, care should be taken to see that the elements are cleaned and replaced regularly as needed. Checks at 25-hour intervals are recommended. Paper elements should be replaced. Oiled foam elements can generally be washed, re-oiled and reused.

Spark Plugs

The spark plug must be properly gapped and free of carbon deposits to ensure proper engine operation. After the spark plug cap is removed, the spark plug can be removed using a spark plug wrench. Always replace a spark plug with the plug recommended by the manufacturer. If the insulator is cracked or chipped, the plug should be discarded. If a plug is to be reused, it should be cleaned with a wire brush before it is reinstalled.

The spark plug gap should be checked using a feeler gauge. Set the gap according to manufacturer’s specs by bending the side electrode. The correct gap will usually be in the .7 to .8 mm range (.028” to 0.31”). The spark plug can be removed from the engine and tested for proper operation. To test the plug, first remove the cap and clean it. Then remove the plug. Install the plug in the cap. Ground the side electrode. Start the engine. If no spark is apparent, the plug should be replaced.

Inspect the spark plug washer to make sure that it is in good condition. When a plug is installed or replaced the plug should be tightened slightly after it is seated to make sure the washer is compressed. If the plug is new, an additional ½ turn may be called for.

Gasoline To Gaseous Fuel Conversion

For a number of applications, engine power and mobility may be needed but gasoline or diesel may not be an appropriate fuel for the environment. This may be the case when engine power is needed indoors or when an engine is used in conjunction with a gas-fired heating unit.

Converting a carbureted gasoline engine to run on a bottled gas supply is one way to combine the benefits of engine mobility with a cleaner burning fuel than gasoline. In some instances, such as use with hot water units, an engine running on bottled gas is safer than an engine using gasoline for a fuel because the opportunity for gasoline vapor from fuel spilled during refueling to build up in the combustion chamber is eliminated.

The Fuel Controller

Most gaseous fuel carburetion systems use a venturi same as a liquid fuel carburetor. In many cases, the same carburetor can be used. When the piston draws air into the system on the suction stroke, the venturi creates a pressure differential at the venturi proportionate to the amount of air drawn into the cylinder. In a liquid fuel system this pressure differential regulates the action of the float and needle valve which control the amount of fuel. When gas is used for the fuel, a fuel controller with a diaphragm regulates the amount of gas allowed into the combustion controller with a diaphragm regulates the amount of gas allowed into the combustion chamber. This fuel controller may be referred to as a “zero governor”. As the diaphragm moves to the low pressure or vacuum side in response to the pressure differential, an attached lever opens a valve allowing fuel to enter the combustion chamber in an amount proportionate to the pressure differential.

The fuel controller or zero governor must be sensitive enough to respond to the full range of fuel demands from the engine but still shut off completely when the engine is not operating. If the fuel controller is not adjusted properly, problems ranging from a lean fuel mixture to the possibility of fire may result.

Important Safety Note:

If equipment converted to gaseous fuel is to be used in any enclosed area the National Fire Protection Association requires a positive fuel shutoff be installed in the fuel system. A lock-off valve or a solenoid valve controlled by a vacuum sensing manifold switch or oil pressure switch can be used to shut off fuel flow. The fuel controller by itself is not considered a proper shutoff for use in enclosed areas.

A constant supply of fuel at a specific, unvarying pressure is also necessary for proper supply of gaseous fuel to an internal combustion engine. A primary pressure regulator is required on units supplied from their own tank. Permanent propane storage installations and natural gas supplies already provide a regulated supply of fuel and a primary regulator is not needed.

Conversion Methods


There are three major techniques for converting a carbureted internal combustion engine to gaseous fuel. The major difference between these methods is the amount of the standard carburetion system replaced during the conversion.

The existing gasoline venturi may be used with a fuel tube inserted in the area of greatest pressure differential. This is called the spud-in system. An adaptor with a special venturi may be added to the carburetor. Or the entire carburetor may be replaced with a special carburetor for gaseous fuel.

NOTE: Make sure that any conversion kit or method is appropriate for the engine being converted. Check the manufacturer’s specifications for any conversion equipment.

The spud-in conversion is the least expensive in terms of component purchase but may prove to be more difficult to install than other conversion equipment. If an adaptor is used for conversion, an idle plate will generally have to be installed between the carburetor and the engine. The adaptor is installed between the air cleaner and the carburetor.

The least time consuming and usually the most expensive conversion method is to simply replace the carburetor with a new one suitable to the engine. This type of conversion usually produces the best performance. In systems which convert liquid propane to a gaseous state a heat exchanger and pressure regulator may be combined in a single device called a vaporizer- regulator or converter. This device may also include a fuel controller or zero governor.

Gaseous Fuel System Problems

Improper fuel controller adjustment can cause a number of problems in the gaseous fuel system. If spring tension against the rubber seat which closes the orifice in the fuel controller is too great and the greater pressure differential is required to open the orifice and allow gas into the system, sluggish progression off idle and lean mixtures and poor performance under load may result. Look for a flat spot on the seal in the orifice. If fuel leaks through the controller at and after shutdown the engine may be hard to start due to an over-rich fuel mixture. If too much fuel passes through the controller a fire hazard may result. Installation of a shutoff device will solve this problem.

Air cleaner pressure drop increases as the air filter element becomes dirty. The pressure differential is increased by this negative pressure effect and fuel mixtures that are too rich may result. An engine converted to gaseous fuel may require priming. That is, fuel may need to be allowed into the combustion chamber before cranking. Many conversion systems allow for priming. An excess flow valve may be installed on the fuel supply to shut off fuel if a fuel line breaks and fuel flow increases suddenly.

Basic Gas Engine Troubleshooting

When a gas engine will not start, first check the fuel tank to see that there is an adequate supply of the proper fuel. If the engine has an electric starter, try to start it using the recoil starter. If it will start using the recoil starter, the battery is likely to be dead. If the engine still will not start, remove the spark plug and sniff for gas in the cylinder. If there is gas present, the engine is probably flooded.

Check the spark plug for carbon deposits. While the spark plug is out, try to start the engine again and see if the plug fires. If the spark plug does not fire, check the plug connection. If the plug connection is okay, the problem is probably the magnet. If no fuel is smelled when the spark plug is removed, check the carburetor float bowl. There is generally a small plug under the bowl. Remove the plug. If no fuel drains from the float bowl, there is a fuel line restriction between the fuel tank and the carburetor. If these procedures do not isolate and correct the engine problem, the engine should be referred to the appropriate gas engine service center unless you are an experienced small engine mechanic.

Note: All equipment should be started with the gun open and the pressure set on low pressure if possible. This reduces the starting load on the engine. If a manually started gasoline engine machine is hard to start, try starting it without the high pressure spray nozzle. This will reduce the load on the engine and may ease starting.

Some new engines may have a circuit breaker installed on electric starting units. This breaker will trip if there is a short circuit or reversed polarity. If pinging (a metallic knocking sound) or “spark knock” occurs when the engine is operated under normal load the brand of gasoline used should be changed or a higher octane fuel used. Heavy pinging and engine damage may result from use of a fuel with an octane rating that is too low. Fuel with a pump octane rating of 86 or higher is generally recommended. Unleaded fuel is generally recommended because use of unleaded fuel produces fewer spark plug and engine deposits and the life of exhaust system components is extended.

Light spark knock may occur when the engine is operated under a heavy load. This simply means the engine is operating properly and does not indicate a problem. Low oil shutoff may be provided for the internal combustion engine. This feature shuts down the engine when the oil level falls too low for safe operation of the engine. Generally an indicator light is lit as well to show the reason for shutdown. If this light is burned out or defective, the reason for shutdown may not be so simple to determine. If the engine does shut down during normal operation, the oil level should be checked as a matter of course.

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