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VALVE TRAIN

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					ENGINE TOP END




                 1
    CYLINDER HEAD
    CONSTRUCTION
Valve guide construction
Valve seat construction
Diesel pre-chamber cup
Stratified charge chamber




                            2
Types of Cylinder Heads
Old fashion
Flatheads
Overhead Valve
(OHV or I-Head)
Single Overhead
Cam (SOHC)
Dual Overhead Cam
(DOHC or Twin
cam)
                          3
         Flathead Engines
All valve train parts are in the
cylinder block.
Cylinder heads have nothing
more than water jackets,
spark plug threaded hole and
some bolt holes.
Tend to be very low
compression. Poor power by
today’s standards.




                                   4
VALVE TRAIN




              5
      VALVE TRAIN
     CONSTRUCTION
Valve construction
Valve seal construction
Valve spring construction
Valve spring shim
Valve retainers and keepers
Valve spring seat
Valve rotators
Valve stem cap

                              6
Valve Train Components
Valve train
components will
vary depending on
the type of head
configuration.
OHV, SOHC or
DOHC



                     7
Overhead Valve Engines
              Has valves in cylinder
              head increasing
              compression.
              Camshaft still in block.
              Uses lifters, pushrods
              and rocker arms.
              Most common head
              design until 1990’s.




                                  8
    Single Overhead Cam
        (OHC)/(SOHC)
Single cam mounted
in head.
Opens both intake
and exhaust valves.
One cam on an
inline engine and
two cams on a vee
engine.


                          9
Dual Overhead Cam (DOHC)

               Camshafts mounted in
               cylinder head.
               One cam opens intake
               valves and one opens
               exhaust valves.
               Often used with 4
               valves per cylinder.
               Most high performance
               of all types.
               Vee engines have 4
               cams.


                               10
DOHC




       11
              Camshafts
Opens the valves at the
right time.
Actually converts rotary
motion to reciprocating
motion.
Uses a cam lobe for each
valve.
Usually made of cast iron.
Has a great effect on
engine performance.
Can be given auxiliary
functions like running the
oil pump or distributor.
                             12
         CAMSHAFT
       CONSTRUCTION
Cam lobes
Camshaft thrust
plate
Cam bearings
Cam housing and
cam cover




                      13
   Cam Lobe Terminology
Heel as known as
the base circle.
Nose is the tip of
the lobe which
determines cam lift.
Opening and
closing flanks and
ramps.
Timing points are
where the cam
starts to open and
close the valve.



                          14
Cam Lobe Lift
          The distance the
          valve is pushed
          open.
          It is determined by
          the height of the
          lobe.




                        15
             Cam Duration

This chart is in
degrees of
crankshaft rotation.
Note when the
valves open and
close and on which
strokes. This is the
duration.
It’s not what it may
seem to be!


                            16
         Camshaft Drives
Gear on gear
Gear and chain
Belt and notched
pulley
Cam gear ALWAYS
is twice as large as
the crank gear, this
makes the cam turn

at   ½      the
speed of the crank.

                           17
   Gear to Gear Drive
Simplest drive
system.
Reliable and strong
but noisy.
Reverses Direction
of Power 2 times
CW>CCW>CW



                        18
Gear and Chain Drive
           Quieter the gear
           types.
           Allows cam to be
           further away from
           crankshaft.




                               19
                Timing Belt

Used primarily on
overhead cam engines.
Uses a kevlar belt.
   (police vests)
Can snap or stretch
causing catastrophic
damage to non-free
running engines.
Chains remain more
popular with engine
makers.

                              20
Installing Timing Chains


             Look for the timing
             marks on the gears.
             Point the marks at
             each other 6 and 12
             o’clock.
             Install cam gear to
             camshaft.



                               21
OHC




      22
OHC direct




             23
OHC intermittent Shaft
            Intermittent Shaft
            drives distributor
            Must Align ALL (3)
            Timing marks!
            Belt tension pulley




                                  24
Timing Variations




                    25
    VALVE &CAMSHAFT
       PLACEMENT
OHC / SOHC
OHV
DOHC
In Block
   I
   T




                      26
VALVE OPERATION




                                                   27
     http://www.howstuffworks.com/engine-cam.htm
          VALVE LIFTERS
Solid Lifters
Roller Lifters
Hydraulic Lifters
Followers




                          28
SOLID LIFTERS




                29
ROLLER LIFTERS




                 30
HYDRAULIC LIFTERS




                    31
FOLLOWERS
   ohc




            32
Valve Lifter Terminology




                       33
Valve Lifters

     Also known as cam
     followers or tappets.
     Come in three
     types: ****
     Mechanical or solid.
     Hydraulic.
     Roller (which can be
     hydraulic or solid).

                         34
        PUSH ROD
      CONSTRUCTION
Hollow tube
Steel
Vary in length
Fit between Lifter
and rocker arm




                     35
                  Pushrods
Metal rod which transfers force from the lifter to the
rocker arm.




                                                    36
 ROCKER ARM
CONSTRUCTION




               37
          Rocker Arms

Rocker arms are
made of stamped
steel, cast iron or
aluminum.
They transmit the
force of the pushrod
to the valve.
Some have
adjusters.

                        38
           Rocker Arms
                              Roller- Stamped
Adjuster   Cast




                  Pivot




                          Stamped

                                          39
                 Valves

Called mushroom or
poppet valves.
Made of high quality
steel.
The exhaust valve has
one of the toughest jobs
in the engine having to
withstand temperatures
of 1300 degrees F.



                           40
Valve Overlap


         This is when the
         intake and exhaust
         valve are open at
         the same time.
         It doesn’t seem right
         but it works.




                        41
   INTAKE MANIFOLD
    CONSTRUCTION
Variable induction
system




                     42
 EXHAUST MANIFOLD
   CONSTRUCTION
Single Exhaust
Dual Exhaust
Single w/crossover
Headers




                     43

				
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posted:9/13/2012
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