Engine Valve Drive Mechanism
Summarized notes
Principles, Types, and Applications in Internal Combustion Engines
,Introduction
This involves the manner in which valves are drive in the engine.
In four-stroke cycle-engine each valve opens once for every two revolutions of
The crankshaft making the camshaft to rotate at half-crankshaft speed, i.e. The
speed ratio of crankshaft to camshaft is 2:1.
Mechanisms used in valve drive are:
1.Chain drives (timing chains)
In this mechanism a chain is used to connect the crankshaft and the camshaft
through their respective sprockets.
The camshaft sprocket is having twice as many teeth as the crankshaft
sprocket.
The timing chain is either a single row type or a duplex with a double row of
rollers.
Camshaft drive component wear will cause the chain to lengthen and a
rattling noise will be heard as the irregular rotation of the camshaft slaps the
chain against the timing cover.
The increase in length is usually corrected by incorporating a chain
tensioner.
1
, Hydraulic adjuster for timing chains
The plunger is forced against the chain by hydraulic oil pressure to
Compensate for chain wear.
A ratchet resists the return travel of the plunger which overcomes the need
for undue pressure on the chain, which would cause power loss and extra
wear.
Oil pressure, supplied from the engine lubrication system, acts on the
plunger to assist the spring in tensioning the chain. When chain or
component wear occurs, the movement of the plunger
Causes the peg to push on the smooth face of the helical slot in the hollow
ratchet and rotate the
Ratchet a small amount. Oil, trapped in the adjuster, acts as a damper and
seepage past the plunger
lubricates the chain.
2. Belt drives
Used on overhead camshaft engines to drive the camshaft or camshafts. The
belt is notched to form equally spaced teeth, which maintains the correct
valve timing.
Belt drives provide a relatively cheap, very quiet and efficient way of
driving a camshaft when it is mounted far away from the crankshaft (e.g.
OHC). A timing belt does not require lubrication and therefore located on
the outside of the engine. This provides ease of disconnection of the belt and
the removal of the cylinder head.
An arrow is usually provided on the timing belt which indicates the direction
of rotation to be fitted. If a timing belt is to be removed and refitted during
engine repairs, the direction of rotation should be noted before the removal
of the belt.
It is constructed using reinforced belt materials such as glass fibre strands or
similar flexible cords. The reverse side of the belt is backed by smooth
rubber, which provides a surface for
The tension to be applied to the belt with a tensioner pulley. The timing belt may
also drive a water pump and balancer shafts.
2
, 3. Chain drive
It is used when the camshaft is fitted close to the crankshaft.the gears are
helical teeth type since they are quite in operation.
Sometimes the large gearwheel is made of a plastic or other non-metallic
material and, in some cases, an idler gear is fitted where the distance
between the crankshaft and the camshaft is large.
COMBUSTION CHAMBER
This is the enclosed space where the combustion of the fuel takes place. The
enclosed volume bound between the cylinder head and the top of the piston.
Factors affecting combustion chamber designs
3
Summarized notes
Principles, Types, and Applications in Internal Combustion Engines
,Introduction
This involves the manner in which valves are drive in the engine.
In four-stroke cycle-engine each valve opens once for every two revolutions of
The crankshaft making the camshaft to rotate at half-crankshaft speed, i.e. The
speed ratio of crankshaft to camshaft is 2:1.
Mechanisms used in valve drive are:
1.Chain drives (timing chains)
In this mechanism a chain is used to connect the crankshaft and the camshaft
through their respective sprockets.
The camshaft sprocket is having twice as many teeth as the crankshaft
sprocket.
The timing chain is either a single row type or a duplex with a double row of
rollers.
Camshaft drive component wear will cause the chain to lengthen and a
rattling noise will be heard as the irregular rotation of the camshaft slaps the
chain against the timing cover.
The increase in length is usually corrected by incorporating a chain
tensioner.
1
, Hydraulic adjuster for timing chains
The plunger is forced against the chain by hydraulic oil pressure to
Compensate for chain wear.
A ratchet resists the return travel of the plunger which overcomes the need
for undue pressure on the chain, which would cause power loss and extra
wear.
Oil pressure, supplied from the engine lubrication system, acts on the
plunger to assist the spring in tensioning the chain. When chain or
component wear occurs, the movement of the plunger
Causes the peg to push on the smooth face of the helical slot in the hollow
ratchet and rotate the
Ratchet a small amount. Oil, trapped in the adjuster, acts as a damper and
seepage past the plunger
lubricates the chain.
2. Belt drives
Used on overhead camshaft engines to drive the camshaft or camshafts. The
belt is notched to form equally spaced teeth, which maintains the correct
valve timing.
Belt drives provide a relatively cheap, very quiet and efficient way of
driving a camshaft when it is mounted far away from the crankshaft (e.g.
OHC). A timing belt does not require lubrication and therefore located on
the outside of the engine. This provides ease of disconnection of the belt and
the removal of the cylinder head.
An arrow is usually provided on the timing belt which indicates the direction
of rotation to be fitted. If a timing belt is to be removed and refitted during
engine repairs, the direction of rotation should be noted before the removal
of the belt.
It is constructed using reinforced belt materials such as glass fibre strands or
similar flexible cords. The reverse side of the belt is backed by smooth
rubber, which provides a surface for
The tension to be applied to the belt with a tensioner pulley. The timing belt may
also drive a water pump and balancer shafts.
2
, 3. Chain drive
It is used when the camshaft is fitted close to the crankshaft.the gears are
helical teeth type since they are quite in operation.
Sometimes the large gearwheel is made of a plastic or other non-metallic
material and, in some cases, an idler gear is fitted where the distance
between the crankshaft and the camshaft is large.
COMBUSTION CHAMBER
This is the enclosed space where the combustion of the fuel takes place. The
enclosed volume bound between the cylinder head and the top of the piston.
Factors affecting combustion chamber designs
3
