This document contains diagrams and explanations of valve and port timing for various engine types. It begins by explaining what engine valve timing is and how the camshaft opens and closes the valves. It then provides diagrams and timing angles in degrees for: 1) A 4-stroke petrol engine valve timing diagram 2) A 4-stroke diesel engine valve timing diagram 3) Port timing diagrams for 2-stroke petrol and diesel engines along with their timing angles. It concludes by providing more details on the theoretical port timing diagram for a 2-stroke diesel engine.

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NO.
Varmora Raxit 150763119027
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I.C.ENGINE VALVE
TIMING DIAGRAM

2. Actual valve timing diagram for 4
stroke petrol engine

3. What is Engine Valve Timing?
• Firstly, read here about how the engine valves
open & close. An automotive engine uses valves
for it’s ‘breathing’ (inhale / exhale) process.
• The engine's camshaft opens and closes the
valves at specific interval. The timing of opening
& closing of valves is specified in degrees
corresponding to the position of engine's pistons.
Engine valve timing is most critical process of IC
engines.

4. Explanation
• IV opens 20˚ before TDC.
• IV closes 35۫ after BDC to takethe advantage of
momentum of rapidly moving gases (Ram Effect).
• Ignition occurs 35˚ before TDC ; this is to allow the time
delay between the spark and commencement of combustion.
• EV opens at 35˚ before BDC; else pressure will rise
enormously, and the work required to expel the gas will
increase.
• EV closes at 10˚ after TDC; this is to increase the
volumetric efficiency.

5. Valve timing diagram for 4-stroke
diesel engine

6. Valve timing diagram angles for 4-
stroke diesel engine

7. Port timing diagram for 2- stroke
petrol engine

8. Port timing diagram angle for 2- stroke
petrol engine

9. Port timing diagram for 2-stroke diesel
engine

10. Explanation
• The theoretical Port Timing Diagram of a Two Stroke Diesel
Engine is shown in the diagram.
• The actual Port Timing diagram may be a bit different from
this theoretical one depending upon the capacity, load, and
need of the engine.
• The exhaust port gets uncovered 60 degrees and inlet port
gets uncovered 45 degrees ahead of the completion of the
second stroke and exhaust port gets covered 60 degrees
and inlet port gets covered 45 degrees after the
compression stroke i.e. second stroke.
• The injection port opens 15 degrees before and closes 20
degrees after the compression.