Valve timing is crucial to the efficient operation of the 4-stroke petrol or diesel engine. The opening and closing
of the inlet and exhaust valves at the correct time in relation to piston position must be precisely controlled,
either at a fixed compromise position, or variable within finely controlled limits.
The valves are opened and closed by the camshaft(s) which are driven by chain, toothed belt or gear train from
the crankshaft.
Intake Stroke
As the piston rises, and at a point just before it reaches TDC, the intake valve opens, and a mixture of fuel and air begin to enter the combustion chamber.
As the piston travels downwards the mixture of fuel and air continues to enter the combustion chamber and at a point just after the piston reaches BDC, the intake valve closes.
Compression Stroke
The air-fuel mixture is compressed as the piston travels upwards to a point just before it reaches TDC, at which time the spark plug fires and combustion takes place forcing the piston downwards.
Power Stroke
As the piston travels downwards, and at a point just before it reaches BDC, the exhaust valve opens and the exhaust gases begin to leave the combustion chamber.
Exhaust Stroke
As the piston travels upwards the exhaust gases continue to leave the combustion chamber and at a point just after the piston reaches TDC, the exhaust valve closes.
Valve timing
It is crucial that the timing marks on the flywheel and camshaft are correctly aligned before removing and replacing the cambelt (timing belt). Check using a maintenance manual (eg: Ha*nes).
Before commencing the engine must be cold.
Remove the sparkplugs to release compression. This will make it easier to turn the crankshaft by hand.
Align the timing mark on the flywheel by turning the crankshaft slowly. On most FWD cars the cranskshaft pulley can be accessed by removing the plastic wheel liner
Before removing the old cambelt the camshaft sprocket wheel must be locked up to prevent rotation. If the camshaft sprocket wheel rotates even slightly when you are fitting the new cambelt a valve timing error is introduced then when the car is started up an increase in tappet noise is heard.
An valve timing error of a just few degrees introduced when replacing the camshaft belt can cause the tappets to sound noisy and this can happen if the cambelt position is 'out' by just 2-3 teeth on the camshaft sprocket wheel. The tendency then is to stop the engine and immediately adjust all the valve clearances to reduce the tappet noise. Do not adjust the tappets because the engine will not fire up when started.
Leave the engine to cool down. The new cambelt must then be removed from the camshaft sprocket wheel and replaced into the correct position ensuring that the timing marks on the flywheel and the camshaft sprocket wheel are lined up together. This ensures that the spark in the cylinder occurs at the correct timing in relation to the position of the piston in the cylinder.
valve timing diagram of two stroke engine
Jason
could you display a diagram of a timing chain for vw polo 1.2 12 valve
variable valve timing is where the engine changes valve timing based on the driving situation much like ignition timing is changed to meet the needs of the engine in specific situations. in most cars valve timing is static and determined by the timing gear on the camshaft
for mechanical and dynamic requirements. By studing correct timing of opening and closing of inlet and exhaust valves improves power and efficiency of engine and reducing of fuel consumption be done.
No such thing. Variable Valve Timing (V.V.T.) - is any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine. Direct Injection - where fuel is injected directly into the (main) cylinders of an engine, esp' in diesels or very rarely in petrol engines.
Valve timing is not adjustable on a stock engine. The timing chain is either installer correctly or not.
Variable timing valve train
The Mitsubishi Canter 4M51 engine does not have a timing belt or chain.
V V T means variable valve timing which are used in petrol engines and other is DDiS means Directs Diesel Injection System which are used in Diesel Engine
Which valve? Engines have many! You need to be very specific about this!
Technically no, but I have seen valve hit valve when the timing belt breaks.