ReviewExam #3

Engine Components

Stroke

The distance swept by a piston as it goes from BDC to TDC or from TDC to BDC.

Stroke vs Throw

Throw is one half (1/2) the stroke

Four StrokesIntake Compression Power Exhaust

5

Basic Engine Components

– Engine Block– Crankshaft– Pistons– Connecting Rods– Camshaft(s)– Intake and Exhaust

Valves

Configuration

The design of the engine block which describes how the cylinders are arranged

Engine Size / Displacement

The combined swept volume of all of the cylinders

Displacement = .7854 x D2 x Stroke x (# of cylinders)Example: Bore (D) = 4 in Stroke = 3 in # of cylinders = 8

Displacement = .7854 x 42 x 3 x 8 = 301.6 in3

Repair Manual Research / Use

Briggs & Stratton Single Cylinder “L” Head Repair Manual

Ignition / Spark TestSet Gap to .030 inchesEnsure spark tester is clipped to a good ground on engine block or cylinder head

Compression TestAt least three to four pulls of starter cordHand tighten into spark plug hole

Cylinder Compression Leaks

Four common locations:Intake ValveExhaust ValveCylinder Head GasketPiston Compression Ring(s)

Combustion Byproducts

CH4 + O2 CO2 + 2H2O + Heat + + CO + HC + NOX

= Good

= Not so Good

Air Intake

Must go through an Air Filter before entering the intake manifold

GasketsA mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression. Gaskets allow "less-than-perfect" mating surfaces on machine parts where they can fill irregularities

FlywheelStores Energy by using inertia/momentum to offset the three non-power producing strokes of the four stroke engine.A larger/heavier flywheel takes more energy to get it rotating up to speed, but it will store more energy and allow for a smoother ride than a lighter flywheel.

Energy ConversionThe Chemical Energy released from bonds breaking in the gasoline is converted (changed) into mechanical energy of the piston traveling down and thermal energy (heat)

Mechanical Energy = 30%Thermal Energy = 70% (half of which goes out exhaust pipe and the other half is absorbed by the engine block /cylinder heads / coolant}

Diameters

Outside

Inside

Vernier Caliper

Toggle between inches, fraction of inches, and mmZeroizeDepth Measurement

Springs

Compression

Tension

Crankshaft TypesCast - pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify.Forged - manufacturing process involving the shaping of metal using localized compressive forcesBillet – originates as a cast or forged block that must be fully machined to take on its shape.

Given the same type of steel (e.g. 4340, 1020, etc) forging will be stronger than casting. Billet has the capability of being stronger than a forged crankshaft.

Crankshaft Measurements

Connecting Rod Journals are same as Crankpin Journals

Gear Ratios

Driven Gear Teeth / Drive Gear Teeth

In a four stroke engine, the cam to crank gear ratio is 2:1

Example is 75/25 or 3:1

ValvesStemTipFace or Seat Margin

Tappet

Engine Tools

Spring Compressor

Valve Lap Tool