power washer parts -The Parts In a 4 Stroke Small Engine

power washer parts - small engine

There are so many parts to a 4 stroke small engine that it makes for a very long article to describe them a "glossary of terms" if you will.
As such,you may wish to read this over several sessions.

So let's begin.

Fuel tank and fuel line. This may be on the side, above, or below the engine intake. A fuel pump may be present - either as part of the carburetor or a separate unit if it is not gravity fed. There may be a fuel cutoff valve and fuel filter and/or filter screen) as well.

Shroud or blower housing. Since these engines are all forced air cooled, (no radiator, water jacket, or thermostat) the proper air flow is extremely important as air is much less efficient than water at removing the substantial heat energy generated by a running engine. This piece of sheet metal precisely guides the airflow. The engine should not be run for any length of time with the shroud or blower housing removed.

Oil filler pipe. On many engines, this is just a hole near the base fitted with a screw-in plug. On fancier models, there is an actual extension tube with a dipstick usually fitting into that hole in the base and sealed with an O-ring.

Starter. Like an automobile engine, some means must be provided to supply an initial rotation.

Pull or recoil starter. This is by far the most common on power washers 13 horsepower or smaller. A self retracting cord wrapped around a one-way clutch acts on the crankshaft directly.

Electric starter. A small motor - powered from a battery - drives the edge of the flywheel via a self releasing gear. The battery is recharged by an alternator while the engine is running.

Air filter. The air used by the engine should be free of dust and larger particles. Most equipment will include different kinds of air filters - paper,or foam are the most common.. . Types of air filters include:

Paper air filter. This is similar to the filter in a vacuum cleaner. The pleated paper element must be replaced when clogged.

Foam air filter. This uses a piece of foam rubber lightly coated with engine oil and can be washed in detergent or soap and water when dirty and recoated though replacement will be required if it is badly deteriorated.

Carburetor. The function of the carburetor is to provide a precise air-fuel mixture to the engine under a variety of operating conditions including:

Starting. A higher ratio of fuel to air is needed when starting and/or the engine is cold.

Idle. Just enough flow is maintained to keep the engine from stalling.

High. Full flow is provided with engine speed limited by feedback from the governor.

Load pickup/acceleration. The proper air-fuel ratio and amount of fuel must be maintained when the equipment is placed under load or encounters an increased load and when switching from IDLE to HIGH, for example.

Several functions are incorporated in a carburetor:

Fuel control - float, diaphragm, suction. A variety of means are provided to maintain a nearly constant supply of fuel despite varying levels of gas in the fuel tank.

Venturi. If you look into the air intake of a carburetor, you will see a narrowing of the passageway. This is called a venturi and results in higher velocity air flow and lower pressure at the center of the narrow section. Just as when you blow across a soda straw submerged in a liquid, or use a bug or lawn sprayer, this lower pressure will suck up the liquid and inject it into the moving air stream. In the care of gasoline, evaporation is almost immediate.

Throttle. A plate that can rotate to close or open the outlet from the carburetor to the engine intake pipe controls the flow of the air-fuel mixture to the engine. When fully closed, the engine will stop. When slightly open, the engine will idle. When fully open, maximum power is developed. To limit rotation speed with little or no load and to maintain proper speed under load, a governor acts on the throttle plate to keep it at the proper setting under all normal operating conditions.

Choke. A plate that can rotate to partially close off the air supply is placed in the air intake side of the carburetor. This is usually set manually when starting, particularly in cold weather, to make the mixture richer - more fuel with respect to air - as needed. The carburetors on most newer equipment have automatic chokes or other methods of accomplishing the same objective.

Flywheel. The flywheel in a small engine serves several functions: Provides some or all of the inertia so the engine can coast through the 3 non-power strokes of the full cycle (4 strokes). Provides the electrical energy for the most common magneto based ignition system. A powerful magnet mounted on the edge of the flywheel passes by a coil (and possibly other stuff) once per rotation. This is part of the ignition system and either provides the high voltage for the spark directly or charges a capacitor which is then discharged (by a solid state switch triggered by the flywheel magnet rotating past a sensor) into an ignition coil at the proper time to generate the spark.

Includes the fan blades which provide most of the essential cooling airflow.

Links to the starting mechanism. For recoil or other manual starters, the starting device attaches to the center of the flywheel. For electric start, the flywheel will have a large gear along the outside that is engaged by the starter motor gear (with an overrunning clutch).

A soft metal key locks the flywheel to the crankshaft. This is designed to shear (break) to protect expensive engine parts should the engine stop abruptly . In this case, the flywheel inertia will attempt to keep it moving and it is better to shear the key than to fracture the flywheel or crankshaft.

Different types of power washers, use various drive systems to couple the pump to the engine crankshaft. These may include gear reducers, or belt drive systems, or a flange designed to directly couple to the pump on direct drive systems. a soft metal key or shear pin is used for protection.

Spark Plug. The ignition source for all small gasoline engines is a high voltage spark. There is nothing magical about a spark plug - it is just an insulated electrode with a specific size gap poking into the combustion chamber. However, damage or fouling (gumming up with carbon or other combustion residue) is one of the most common causes of a hard or impossible to start engine. Not all spark plugs are created equal despite their simple function so the recommended replacement type should always be used.

Magneto ignition. These used to use mechanical contact points - controlled by a cam on the crankshaft to determine the timing. Nowadays, most are fully electronic and require no maintenance.

Point type. The magnet mounted on the flywheel induces a current in a coil with pole pieces mounted in close proximity to the flywheel. When this current is near its peak, a set of contacts operated by a cam on the crankshaft - the breaker points - open interrupting the current and diverting it to a condenser (capacitor). The current drops abruptly and induces a high voltage in another coil wound on the same core. This coil is connected to the spark plug terminal. It will be 10 kilovolts or more to jump the spark plug gap even under the more difficult conditions during maximum compression. The exact time - angle of the crankshaft - at which the points open is the critical setting. This is usually adjusted by moving the piston to a specific dimension below Top Dead Center (TDC) or aligning timing marks on the flywheel and crankcase and setting the points to just open at this location.

Electronic type. These can be designed in several different ways but all must emulate the behavior of the point type ignition replacing just the magneto coil/pole piece assembly and without requiring alterations to the flywheel.

Engine block. The casting which includes the cylinder, crankcase, intake and exhaust ports and valve guides and seats. The other major part of the engine structure is the crankcase cover/oil sump.

Cylinder. This is the, well, cylindrical component in which the piston moves. Most small engines are made of either aluminum (most common these days) or cast iron. In most cases, the aluminum type will have a cast iron liner for long life where the piston actually slides. With regular oil changes, there will be virtually no wear.

Cylinder head. (or just head). The cap which encloses one end of the cylinder. On most small engines, the only component mounted in the head is the spark plug which screws into a threaded hole. However, on the most modern (and expensive) small engines (as well as all automobile engines), the valves will also be mounted above the piston in the cylinder head. Fins on the head increase its surface area - absolutely necessary for these air cooled engines to keep their cool

Crankcase. This encloses the lower working parts of the engine and also contains the oil supply. The flywheel/magneto end main bearing is mounted in one end of the crankcase. The crankcase cover/oil sump seals the crankcase.

Valves. These look like metal mushrooms and seat against metal rings mounted in the engine block casting. They are spring loaded in the closed position, slide in valve guides (bored holes), and are operated by valve lifters from cams on the camshaft.

Intake valve. This valve is opened only during the intake stroke. It is subjected to less stress than the exhaust valve as it is cooled by the fresh air-fuel mixture. The intake valve may be stamped with an I.

Exhaust valve. This valve is opened only during the exhaust stroke. It is subjected to more stress than the intake valve since the hot exhaust gases pass out through its opening. The exhaust valve may be marked with an E.

Note: that in most small engines, the valves are not mounted above the cylinder (in the head) as they are in automobile engines. Rather, they are mounted on the side of the cylinder in the engine block. This is done for reasons of cost requiring fewer parts and simpler construction. The cylinder head is then just a casting with cooling fins and a threaded hole for the spark plug. The disadvantage of the side valve engine is lower efficiency and higher pollution.

The newest and best power washers are incorporating the better overhead valve technology. Eventually, environmental protection laws may force this on all small engine operated devices. However, both types can apparently be made to meet the emissions standards mandated for equipment sold after September 1996.

Valve lifters (tappets). These also look like metal mushrooms with the wide part riding on the cams of the camshaft. Their ends press on the ends of the valve stems to open them during the appropriate part of the cycle.

Compression release. This mechanism reduces the compression somewhat at low rpms (to make starting easier) by opening the exhaust valve slightly early. A weight disengages the compression release once the engine starts.

Piston. The piston is a cylindrical closed ended plug that slides in the cylinder and is acted upon by the hot gases during combustion. In small engines, it is usually made from an aluminum alloy. Power is obtained by the piston driving the off center crank pin journal on the crankshaft via the connecting rod.

Piston rings. Springy split rings of cast iron (usually) which fit in grooves or slots around the piston. When the piston with rings is installed in the cylinder, the rings expand and tightly contact the cylinder wall forming a remarkably good seal.

Piston pin (or wrist pin). The piston is attached to the connecting rod via a polished steel pin (actually a tube) which fits closely in a bearing in the connecting rod.

Connecting rod (or just rod). A rod with bearings at both ends. Small 4 stroke engine rods are usually made of an aluminum alloy and have no special bearing inserts at either end. 2 stroke rods will have needle bearings due to the type of lubrication available.

Crankshaft. The main rotating part of the engine. See the diagram in the section below Crankshaft anatomy

Read Crankshaft Anatomy

Crank pin journal. The offset surface where the connecting rod bearing rotates. The is the bearing with the most stress as the full force of each power stroke is applied here. It is the location where damage will likely show up first due to contaminated oil or lack of oil.

Counterbalance weights. These two massive weights are part of the crankshaft casting opposite the crank pin journal. They help to reduce the vibration of the engine by partially counteracting the forces of the piston and connecting rod as they move back and forth. Larger engines may have additional rotating balancer shafts which can be designed to do a better job of minimizing vibration than just the counterbalance weights on the crankshaft.

Crank gear or timing gear. A small gear mounted on the crankshaft which rotate the camshaft at half the crankshaft speed to control valve timing. The crank gear has half as many teeth as the camgear.

A precision taper is located at the magneto/flywheel end for mounting the flywheel and starter components.

A cam (possibly removable) may be present under the flywheel location for operating the breaker points on a point type ignition system.

Camshaft. This includes the two cams which operate the valves and runs at 1/2 the speed of the crankshaft.

Oil/lubrication device. Several types of mechanisms are used to distribute engine oil to all the critical parts in a small engine:

The piston rings (oil ring mainly) scrape oil off of the cylinder walls which passes through holes in the oil ring grooves of the piston to lubricate the piston pin at the top of connecting rod.

All other important parts are lubricated typically by one of the following devices:

Oil dipper. An extension to the connecting rod dips into the oil sump on each rotation of the crankshaft and provides lubrication by literally just splashing oil onto where it is needed.(Horizontal crankshaft engines only.)

Oil slinger. A pinwheel like affair rotated off of the crankshaft or camshaft flings oil onto where it is needed. (Horizontal or vertical crankshaft engines.)

Oil pump. A camshaft driven pump distributes oil to the important parts via various passages in the camshaft, engine block, and possibly the crankshaft and connecting rod as well. (Horizontal or vertical crankshaft engines.)

Governor. This provides the feedback to the carburetor throttle plate to regulate the engine speed (usually for anything but idle speed).
Thus, the speed is maintained relatively constant despite changes in load and engine temperature.

Air vane governor. The air flow provided by the flywheel/blower passes by a plate which is coupled to the carburetor throttle plate acting against a spring force.

Flyweight governor. A spinning gear assembly with a pair of weights is driven by the camshaft. As the centrifugal force of the weights increases, they move a sleeve which presses against a lever whose shaft passes through the crankcase. This lever then operates the carburetor throttle plate against a spring force.

With both types, increasing the spring force will increase the engine speed.

Breather. Since the crankcase is otherwise sealed with the piston moving up and down or in and out, some means is required to maintain a negative pressure or else oil might be forced out various places like the bearings and oil seals. The breather is a leaky one way valve which easily passes air out but is mostly blocked in the other direction.

Muffler. The muffler mounts on the exhaust port and serves two important functions:

Noise reduction. As its name implies, the muffler muffles or reduces the loud noise resulting from the explosions of the air-fuel mixture.

Spark/flame arresting. The internal baffles of the muffler prevent most sparks or flame from existing the engine even if it backfires.

Oil seals. These are spring loaded rubber rings which prevent the escape of oil through the main bearings to the outside.

Whew,quite a few parts. While not meant to be a service primer we hope this gives an appreciation of the engineering involved and an insight into the critical importance of regular maintenance.