Lubrication- Purpose Is to Minimize Friction and Wear

Engine Systems Lubrication- purpose is to minimize friction and wear Oil prevents metal from rubbing against metal Layers of oil cover the metal surface and hold the two metals away from each other Jobs that oil does: Oil reduces power loss and wear of metal parts It removes heat from the engine Absorbs shocks between bearings and other engine parts Forms a seal between the piston rings and the cylinder wall Acts as a cleaning agent

Viscosity is a measure of an oils resistance to flow Thick liquids move slow Tin liquids move fast

Two cycle engines use a total loss system

Two ways to classify four cycle engine lubricating systems Where the oil is stored: wet sump/dry sump How oil reaches the moving parts/ by splash or by pressure feed Wet sump cars most small engines use wet sump- oil pan – crank case is where oil is stored Oil pump or splash lubrication Wet sumps are not good for rough areas Dry sump- double pump one is a scavenging pump and the other is a pressure pump second pump always has oil to draw from

Types of oil delivering systems: Splash method a dipper is on the lower end of the connecting rod or a small slinger that is rotated by the cam shaft gear Others can be operated by a barrel type plunger to provide a pressurized lubricating system Pressurized lubricating system an oil pump sends oil from the crank case to holes or nozzles from which oil sprays onto the moving parts

Fuel systems: include fuel tank, fuel filter, carburetor, air cleaner and possibly a fuel pump Three types Gravity feed Suction feed Pressure feed

Types of air cleaners: Metal mesh moisten with oil Oil bath reservoir of oil Oil foam Dry element filter paper

Carburetor The essential parts are a air cleaner, float bowl, choke valve, throttle valve and some a fuel nozzle with adjustment needles Float bowl prevents the delivery of too much fuel to the carburetor With out this device all the fuel from the tank would run into the carburetor The float bowl consist of a small bowl, a float and a needle valve operated by the float

The basic carburetor beside the float bowl consists of an air horn the fuel nozzle and a throttle valve The throttle valve controls the flow of air into the carburetor basic control of the engines speed and power also controls the air fuel mixture coming into the engine

The air horn has a restriction called the venturi, at the point where the fuel nozzle enters the air horn The venture creates a partial vacuum ( low pressure area) when air is passing through the air horn In the carburetor venturi, this vacuum is located around the end of the fuel nozzle The air pressure on the fuel in the float bowl pushes the fuel up the tube and out the fuel nozzle The fuel sprays into the passing air mixing with it to form the air fuel mixture that the engine needs to operate More air-more vacuum-more fuel Choke its purpose is to help start the engine it creates a greater vacuum at the fuel nozzle to create a more fuel enriched mixture

Governors when load varies but steady speed is required prevent engine from stalling or over speeding Two types of governors air vane and centrifugal Do not adjust to allow fro greater engine power

Engine cooling systems Air cooled and liquid cooled Designed to remove 30-35% of the heat produced during combustion Air cooled most small engines cylinder heads have fins increase outer surface area Open motor cycles Forced air small engines

Liquid cooling systems circulates water around the cylinder and through the head to carry away excess heat – cars Radiator heat exchanger coolant tubes an air passages Cool air is pulled through radiator by engine fan continuous circulation A thermostat is placed on coolant passage between cylinder head and the top of radiator Closed when cold slowly opens when engine warms up to allow flow of coolant Please Prepare a presentation on: The ignition system The exhaust system The starter system