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. Four stroke diesel theory Compression ignition Diesel fuel low volatility High compression ratios produce the heat necessary Pre-chamber for vaporization

7. Rotary engine theory

8. Piston dwell time Piston travel is at a minimum. . . TDC and BDC Crank moves horizontally Piston velocity Maximum when rod is 90 ° to crank Acceleration Maximum 30 ° earlier Best VE is obtained by synchronizing valve opening with piston speeds

9. 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

10. 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

11. 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

12. Combustion Spark ignition Maximum cylinder pressure 15 ° ATDC Tumble and swirl Motion reduces misfires Excess motion inhibits flow AFR 14.7:1 at part throttle, 12.5:1 under load Compression ignition 18:1 direct injection 23:1 pre-chambers for better starting Cranking heats air to 600 °F Compression heats are to 800-1200 °F

13. Diesel fuels Cetane volatility numbers 50-55 Higher cetane #1 fuel for cold weather Lower cetane #2 fuel for warm weather Paraffin separates from fuel at 20°F

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

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

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

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

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

22. Other lash compensators

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

27. 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

28. Engine oiling Lubrication through pressure. . .

29. Engine oiling and spray. . .

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