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What is the significance of Valve Timing Diagram ? How To Draw Valve Timing Diagram For Four Stroke Petrol Engine?



What is the significance of Valve Timing Diagram ? How To Draw Valve Timing Diagram For Four Stroke Petrol Engine?


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Valve timing diagram is a simple diagram which shows the position or opening closing time of both inlet and exhaust valves with respect to crank rotation angle. In which TDC and BDC are taken as two references for crank angles.

Drawing a valve timing diagram for a four stroke engine.

1. Draw two references TDC and BDC at an angle of 180 degree to each other.

2. Start from TDC when piston starts to move towards BDC. Check after how much rotation of crank w.r.t TDC, Inlet starts to move to open the inlet port for suction. Mark that angle and draw a line from center with same angle with TDC.

3. Now check at which angle of crank with BDC inlet returns back to close the port. Mark that angle and draw a line with that angle with reference BDC.

Repeat the procedure w.r.t to BDC and TDC for Exhaust Valve, Draw a spiral moving towards the center pointing position of valves.

Consider clockwise direction while drawing. Will get the valve timing diagram of that four stroke engine in observation.

Quite difficult to measure exact crank angle practically so standard values are considered for drawing this diagram.

While designing an engine cam and timing gears are the key element to vary the valve timing according to design.

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we can draw ideal diagram with equal distribution of the degrees for every strokes. but at the high rpm rotation the ideal diagram is inefficient because insufficient amount of fuel mixture entry and incomplete scavenging. so giving some advanced degrees on valve timing that gives efficient fuel mixture admission and scavenging process completion. that s why the  inlet valve opening before tdc and closing after bdc. and exhaust opening before bdc and after tdc.

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