Engine Terminology Engine Dynamics The Four Strokes Lesson

Engine Terminology Engine Dynamics The Four Strokes Lesson 6 March 2008

Spot Quiz Ø Laws of Mechanics Ø Top 5 Ø Bottom 5 Ø Applied Laws of Mechanics You. Tube - 3 D animation of a car engine

In order for an engine to function properly: Ø the correct fuel charge must be delivered to the cylinder at the correct time. Ø ignition of the fuel charge must occur at the correct time. Ø the cylinder must be purged of spent gasses at the correct time.

Simplified An easier way to remember is that an engine must have: ØSpark ØFuel ØTime

Engine breathing dynamics 1) Intake 2) Compression 3) Power 4) Exhaust

Crankshaft – stroke control In true terms, a stroke is the upward or downward movement of the piston in the cylinder from TDC to BDC once (1)

TDC - BDC TDC – means Top Dead Centre BDC – means Bottom Dead Centre

The ‘stroke' is the measurement between crankshaft main journal and connecting rod journal (throw) multiplied by 2

Crankshaft Rotation- 4 strokes 720 degrees (two revolutions) 0 - 180 -360 360 -540 540 -720

The 4 Events • Intake (suck) • Compression (squeeze) • Power (bang) • Exhaust (blow)

Camshaft-the breathing brain

Remember how the Crankshaft sees 720 degrees ? 0 - 180 -360 360 -540 540 -720

How the Camshaft views 720 degrees of Crankshaft rotation How many times did the camshaft turn to complete all four events?

Crank-Cam Connection Mechanical Valve Timing The camshaft is timed (aligned) to the crankshaft so that the valve ‘events’ occur during the appropriate ‘stroke’. This alignment must be precise or engine damage could occur.

Timing Marks (Cam and Crank in sync)

Remember l Stroke is the piston moving from TDC to BDC once (controlled by crankshaft) l Event is opening and closing of valves (controlled by camshaft and valve springs)

The 10 Pieces - Intake Stroke Cause and Effect (advanced diagnostics) Bottom End Top End • Block • Head • Piston (rings) • Valve • Wrist pin • Spring • Connecting Rod • Cam • Crankshaft • Belt (or other drive)

Intake Stroke and Event Ø Intake valve OPEN Ø Exhaust valve CLOSED Ø Piston on down stroke

The 10 Pieces-Compression Stroke Cause and Effect (advanced diagnostics) Bottom End Top End • Block • Head • Piston (rings) • Valve • Wrist pin • Spring • Connecting Rod • Cam • Crankshaft • Belt (or other drive)

Compression Stroke and Event Ø Both valves CLOSED Ø Piston on upward stroke

The 10 Pieces- Power Stroke Cause and Effect (advanced diagnostics) Bottom End • Block Top End • Head • Piston (rings) • Valve • Wrist pin • Spring • Connecting Rod • Cam • Crankshaft • Belt (or other drive)

Power Stroke and Event Ø Both valves CLOSED Ø Piston on downward stroke

The 10 Pieces-Exhaust Stroke Cause and Effect (advanced diagnostics) Bottom End • Block Top End • Head • Piston (rings) • Valve • Wrist pin • Spring • Connecting Rod • Cam • Crankshaft • Belt (or other drive)

Exhaust Stroke and Event Ø Intake valve CLOSED Ø Exhaust valve OPEN Ø Piston on upward stroke You. Tube - How Engines Work You. Tube - Soldiers blow up washing machine with a grenade