Automobile Engineering in ME
It is necessary to maintain the valve clearances as they

Allow for lengthening of the valves owing to the heat of combustion
Reduce the resistance to sliding that occurs between the cam and the tappet
Increase the speed at which the valves move up and down
Make the crankshaft turn smoothly

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Automobile Engineering in ME
The main characteristics of a maintenance free (MF) battery is that

Recharging of a maintenance free battery is neither required nor possible
A maintenance free battery requires little maintenance during normal use and it is sufficient to add water instead of an electrolyte containing sulphuric acid
A maintenance free battery has a relatively short shelf life when compared with standard batteries
Since it is sealed, the water in maintenance free battery is not lost through evaporation thus accordingly it is not necessary to top up the cells with water

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Automobile Engineering in ME
The function of positive crankcase ventilation (PCV) system is that it

Promotes combustion by creating a swirling movement in the air-fuel mixture
Feeds blow by gases to the exhaust manifold
Returns blow by gases from the crankcase to the intake system
Mixes fuel with air

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