1. Camshafts, Lifters, Timing Belts, and Chains
Chapter 9
Camshafts, Lifters, Timing Belts, and Chains

2. Objectives Analyze theories of camshaft and related parts
Describe operation of hydraulic lifters and lash adjusters

3. Objectives
Install single and dual overhead camshafts with correct valve timing
Verify valve timing and be able to correctly position a camshaft in relation to TDC

4. Camshaft Located in block or on cylinder head
Cam in block design is typically called a pushrod engine
Made from hardened cast iron or steel
Cam has one lobe for each valve
Some engines have multiple cams

5. Controlling Camshaft End Thrust
On some engines
Resistance from driving the oil pump causes cam to be forced backwards
Rearward movement of cam is called end thrust
Could affect ignition timing in a distributor type engine

6. Controlling Camshaft End Thrust
Thrust plates and machined areas on the back of the timing chain gear
Used to control end thrust

7. Controlling Camshaft End Thrust

8. Valve Lash (OHC) OHC engines
Valve clearance adjusted hydraulically while others have provisions for adjustment

9. Valve Lash (OHC)
Some OHC engines have cam lobes that act directly on the valves
On these type engines, lash is adjusted by adding or removing shims

10. Valve Lash (OHC)

11. Valve Lifters Mechanical or hydraulic Two types
Mechanical are also referred to as solid lifters or tappets
Two types
Flat tappet
Roller

12. Hydraulic Lifter Operation
When clearance occurs in valvetrain
Spring between plunger and lifter body causes lifter to expand
Oil fills cavity created under plunger
Excessive oil in lifter leaks down between plunger and lifter body

13. Hydraulic Lifter Failure
Causes of hydraulic lifter failure
Dirt lodged in check valve
Too much wear between plunger and lifter body causing excessive leak down
Insufficient oil pressure
Varnish between plunger and body

14. Cam Lobe Shape
Base circle
Opening and closing ramp
Lift
Duration

15. Cam Lobe Shape

16. Valve Timing Intake valve opens before TDC
Allows cylinder to fill with air-fuel mixture
Intake valve remains open after BDC
Exhaust valve opens considerably before end of power stroke
Exhaust valve remains open past TDC, partly into intake stroke

17. Valve Timing

18. Roller Cam and Lifters
Accept higher rate of movement without wear to lifter or cam lobe
Valvetrain friction cut in half
Increase in power and fuel economy
Roller lifters use brackets to keep them from spinning

19. Roller Cam and Lifters

20. Freewheeling and Interference Engines
Interference engines experience piston-to-valve contact if timing belt or chain breaks
Damage may occur to pushrods, pistons, and valves
Freewheeling engines will not damage valvetrain in the event of a timing belt-chain failure

21. Timing Chains Two types of chains:
Roller chain
Silent chain
Roller chains have single or double rows
Timing chains have drive side and a side where slack accumulates

22. Timing Chains

23. Checking Timing Chain for Stretch
Observe dwell section of ignition waveform on a scope
While watching distributor rotor, turn vibration damper back and forth Movement should be less than 5º
Measure chain slack with timing cover removed

24. Timing Chain Tensioners
Used on OHC engines with long timing chains
Should be replaced when chain is replaced

25. Chain Drive Timing Marks
Some manufactures specify a certain number of chain links between marks
Some have colored links that must be aligned with marks on sprockets

26. Chain Drive Timing Marks
Some have a mark on cam sprocket that lines up with a mark on cylinder head
Some OHC engine have a drive chain and one or two auxiliary chains

27. Timing Belts Drive camshaft on OHC engines Compared to timing chains
Quieter
Require no lubrication
More efficient
Very strong and durable
Sometimes drives coolant pump and oil pump

28. Timing Belt Materials Neoprene High-temperature neoprene
Highly saturated nitrile

29. Timing Belt Inspection
Look for fraying, cracks at base of teeth or loose fibers
Rotate engine by hand to inspect entire belt

30. Timing Belt Inspection
Wear on one side of tooth indicates misalignment problem
Check for oil leaks which could damage belt

31. Timing Belt Inspection

32. Timing Belt Replacement
Replacements will be done on a preventative maintenance basis, or when they fail.
Use a non-petroleum based solvent to clean sprockets
Inspect sprockets for wear
Inspect or replace front camshaft oil seal
Cogs can strip off the belt, resulting in serious engine damage

33. Timing Belt Replacement
Adjust belt tension according to manufacturer specification
Place sticker on valve cover or door post listing mileage when belt was replaced

34. Automatic Belt Tensioners
Some are spring loaded and must be unloaded before belt can be installed
Some tensioners have a specific clearance measurement that is adjustable and measured with a feeler gauge

35. Automatic Belt Tensioners
Some require belt tension gauge to set proper timing tension

36. Automatic Belt Tensioners