1. Four stroke cycle theory
Intake stroke
Piston moving down
Intake valve open
Exhaust valve closed
Copyright 2003 Gary Lewis - Dave Capitolo

2. Four stroke cycle theory
Compression stroke
Piston moving up
Intake valve closed
Exhaust valve closed

3. Four stroke cycle theory
Power stroke
Piston moving down
Intake valve closed
Exhaust valve closed

4. Four stroke cycle theory
Exhaust stroke
Piston moving up
Intake valve closed
Exhaust valve open

5. Four stroke cycle theory
Each stroke takes 180° of crankshaft rotation to complete
All cylinders fire in 720° of crankshaft rotation
720 divided by number of cylinders = firing interval
Odd fire V-6 engine (90° block with 120° rod journals)

6. Other engine cycles
Overlap
Both valves are open
End of exhaust & start of intake
Low pressure in exhaust port
Blowdown
Exhaust valve opens before BDC
To help evacuate cylinder before piston reverses
Pumping losses at end of exhaust stroke

7. Valve events
Intake valve opening
BTDC
Low pressure in cylinder
Intake valve closing
ABDC
Cylinder pressure is effected by timing
Exhaust valve opening
BBDC
Residual pressure helps blowdown
Exhaust valve closing
ATDC
Low pressure in exhaust port draws air in

8. Effects on valve timing
Intake valve opening
Late – Reduced VE
Early – Dilution of intake with exhaust
Intake valve closing
Late – Reduces cylinder pressure
Early – Increases cylinder pressure
Exhaust valve opening
Late – Pumping losses
Early – Power reduction
Exhaust valve closing
Late – Reduces vacuum
Early – Reduces VE

9. Valve trains
OHV (overhead valve)
Pushrod configuration
Many reciprocating parts
Higher valve spring pressure required
Compact engine size compared to OHC

10. Valve trains
OHC (overhead cam)
Fewer reciprocating parts
Reduced valve spring pressure required
Higher RPM capability
Cylinder head assemblies are taller

11. Valve trains
Cam-in-head
No pushrods
Use rocker arms

12. Valve lash compensators
Solid lifters
No internal parts
Periodic adjustment

13. Valve lash compensators
Hydraulic lifters
To maintain zero lash
Quieter
No periodic adjustment
Anti-scuff additives are required in oils

14. Hydraulic lifter operation
Valve closed
Oil flows through lifter bore, &
past check valve
Plunger return spring maintains
zero lash

15. Hydraulic lifter operation
Valve open
Check valve seats and limits the slippage
Now operates as a solid lifter

16. Hydraulic lifter operation
Return to valve closed
New oil enters the lifter body
This oil replaces oil that has leaked between
plunger and body (predetermined leakage)

17. Other lash compensators

18. Metering device
Metering valve meters the
oil flow to the pushrod

19. Timing sets
Gear sets
Cam and crank rotate in opposite directions
Noisy if not free of burrs
Helical and spur cut gears

20. Timing sets
Timing chains
Single and double roller
Tensioners

21. Timing sets
Timing belts
Require maintenance
Quiet

22. Camshaft terminology
Cam lift (A-B)
Valve lift = Cam lift times
rocker ratio
Valve lift
.300” cam lift times
1.5 rocker ratio =
.450” valve opening

23. Engine oiling
Lubrication through pressure. . .

24. Engine oiling
and spray. . .

25. Engine oiling
Oil pan baffles
To keep oil in sump during braking,
accelerating, and cornering

26. Engine oiling
Oil pan windage tray
To prevent oil aeration in the sump

27. Engine oiling
Oil pumps
Driven by distributors, gear on camshaft, or crankshaft

28. Engine oiling
Oil pumps with pressure relief valves
Gear type pump
Rotor type pump

29. Engine oiling
Full flow oil filtering system
Oil pump output flows
through filter first
Bypass circuit for restricted
filters will allow oil to
flow to engine

30. Engine oils
API, SAE, and ASTM
“S” - Spark ignition
“C” - Compression ignition

31. Engine oil additives
Viscosity index improvers
To reduce viscosity change with heat
Detergents
To dissolve varnish and sludge
Dispersants
To keep sludge, carbon and other materials from
recombining and suspends them in oil to be drained
Scuff inhibitors
To reduce friction and wear
Antifoam and antioxidants
To prevent foaming and to slow oxidation in oil

32. Engine measurements
Bore
Diameter of cylinder
Stroke
Distance between TDC & BDC

33. Engine measurements
Displacement per cylinder
 r² S
Displacement for the engine
Disp per cylinder times the
Number of cylinders

34. Engine measurements
Compression ratio
PD + CV CV
To calculate clearance volume
PD .
CR-1

35. Engine measurements
Deck clearance
Top of piston to top of block deck
Measured with dial indicator or depth mic

36. Engine measurements
Deck height
Center line of crank to block deck

37. Fits and clearances
Running fit
Clearance between bearing and shaft
Clearance for oil
Listed as diametral

38. Fits and clearances
Interference (press) fit
OD is larger than ID
Example is piston pin pressed into rod

39. Fits and clearances of pistons
Full floating
clearance in rod
clearance in piston
Press Fit
interference in rod
clearance in piston
Rod offset
Beam offset to center of cylinder
Enlarged chamfers to clear fillets
Pin offset
Offset to major thrust side
Quieter engine, less cylinder wear

40. Cooling system operation
Engine heat is transfered . . .
through walls of the combustion chambers
through the walls of cylinders
Coolant flows . . .
to upper radiator hose
through radiator
to water pump
through engine water jackets
through thermostat
back to radiator

41. Cooling system operation
Fans increase air flow through radiator
Hydraulic fan clutches
Hydraulic fans consume 6 to 8 HP
Electric fans
Coolant (ethylene glycol)
50/50 mixture increases boiling point to 227°F
pressurizing system to 15 PSI increases to 265°F
Coolant (propylene glycol)
Less protection at the same temperatures
Less toxic

42. Cooling system operation
Heat energy
1/3 usable power
1/3 released through exhaust system
1/3 released through cooling system
Engine temperature
Cool enough to prevent part failure
Warm enough to maximize engine efficiency

43. Coolant Types
Traditional American coolants
High silicates, should be changed every 24mos.
American low silicate coolant
Longer life span
Heavy duty coolant
Low silicate, require additive
Fully formulated (pre-charged)
Same as above, but additives already in it

44. Coolant Types
Japanese coolants
Many colors. No silicates. Uses other additives instead of silicates
Organic Acid Technology
Dexcool, European coolants
Hybrid coolants
Aluminum and cavitation protection