2. 18
Camshaft and Valve Train Service

3. Learning Objectives Explain how to inspect and service the camshaft.
Summarize service procedures for in-block and overhead valve assemblies.
Describe the steps in inspecting and reconditioning valve seats.
Explain how to inspect and recondition valve lifters and valve guides.

4. Introduction to Valve Train Service
Valve train performs several vital functions
Allows air-fuel mixture into cylinder
Seals combustion chamber during compression
Allows exhaust gases to exit cylinder
Damaged parts must be reconditioned or replaced
Also, parts in contact with damaged parts

5. Camshaft Service Inspect camshaft for wear or damage
Bearing surfaces, lobes, timing gear
Timing gears need to be replaced in pairs
Measure journals and lobes for wear
Measure bearing bores in crankcase and cover
Check compression release mechanism for proper operation

6. Measuring a Camshaft Bearing Journal

7. Measuring a Camshaft Bearing Bore

8. Measuring a Camshaft Lobe

9. Valve Service 4-cycle engines have poppet valves
Exhaust valves subjected to high temps
Made from high-quality, heat-resistant steel
Proper operating clearance must be maintained

10. Inspecting Valves and Seats
Clean valves with power wire brush
Inspect valves
Damaged faces, heads, or stems
Warped valve head
Worn, improperly ground, or bent stems
Thin margins or partial seating
Replace or refinish damaged valves

11. Inspecting Valve Springs
Overheating and wear damage springs
Lose elasticity
Become warped or distorted
Check squareness and length with square
Replace if improper length or warped

12. Valve Guides Align valves with valve seats Clearance must be correct
Allows for heat expansion and lubrication
Valve tipping causes improper seating
Proper clearance is typically .002 to .003
Replaceable valve guide inserts
Integral valve guides

13. Types of Valve Guides

14. Inspecting Valve Guides
Must be cleaned before inspection
Cylindrical wire brush
Determining clearance
Measure valve guide with small hole gauge
Measure valve stem with micrometer
Guide diameter minus valve stem diameter
Some guides measured with plug gauge

15. Correcting Worn Integral Valve Guides
Ream guide and install replacement valve
Valves with oversize stems must be available
Ream valve and install thin-walled bushing
Bushing must be reamed with finish reamer
Wash all chips away with penetrating oil

16. Valve Guide Bushing Replacement
Refer to manufacturer’s service manual
Depth of guide is measured
Iron guides driven out through the bottom
Brass guides pulled out through top
Replacement guide pressed into bore
Same depth as old bushing

17. Pulling a Soft Metal Valve Guide
(Briggs & Stratton Corp.)

18. Refacing Valves Can be ground with abrasive stone
Can be cut on special lathe
Can be cut with manual cutter
Cut to 30 or 45

19. Valve Cutting Lathe
(Neway Mfg. Co.)

20. Manual Valve Refacer
(Neway Mfg. Co.)

21. Valve Lifter Service Inspect valve lifter contact surface
Concavity, scoring, deformities
Insert lifter in guide and check for play
Should move freely in guide
Lifter should not wiggle in its guide
Side play can be measured with a dial indicator

22. Measuring Valve Lifter Side Play with a Dial Indicator

23. Valve Seat Service Should always be reconditioned or replaced
Inspect seat for looseness or damage
Some seats are replaceable
Some seats are an integral part of block
Must be bored out and seat insert installed
May be more practical to replace block

24. Peening a Valve Seat Insert
Peening secures loose seat
Place insert squarely in its bore
Seat insert using centerpunch and hammer
Three points equidistant around rim
Use drift punch to indent block material outside insert’s rim
Work around rim in a star pattern

25. Peening a Valve Seat Insert
(Briggs & Stratton Corp.)

26. Valve Seat Angle and Width
Valve seats generally cut to 45 or 30
Some seats cut with 1 interference angle
Valve seat width must be correct
Wide enough to prevent cutting into valve face
Enough contact surface for heat dissipation
Not so wide as to cause carbon buildup
Typically .030 to .060

27. Refacing (Cutting) Valve Seats
Special cutting tool with carbide blades
Seat condition determines amount of cutting
Cover seat area in ink before cutting
Makes progress easier to see

28. Refacing (Cutting) Valve Seats
Place pilot in valve guide
Slide cutter over pilot
Install T-handle and use it to turn cutter
Moderate downward pressure
Clockwise direction only
Remove cutter and check progress
After cutting seat, wash away chips

29. Valve Seat Cutters
(Neway Mfg. Co.)

30. Replacing Valve Seat Inserts
Damaged seat inserts pulled
Use special puller, slide hammer, or pry bar
Replacement insert is installed
Chamfered edge down
Peened in place
Some integral seats replaced with insert
Reface newly installed seat inserts

31. Driving In a Valve Seat Insert
(Briggs & Stratton Corp.)

32. Lapping Valves Lapping compound is grease and abrasives Procedure:
Course and fine grades
Procedure:
Apply lapping compound to valve face
Attach lapping stick to valve head
Place valve in guide and twirl
Finished when gray band appears on valve face
Clean valve and block after lapping

33. Lapping Valves

34. Valve Lifter-to-Stem Clearance
Space between lifter and end of valve stem
Exhaust valve typically has greater clearance
Too little clearance
May keep valve open, burning valve and seat
Advances valve timing
Too much clearance
Reduces valve lift
Rapid lifter wear

35. Proper and Improper Valve Clearance

36. Adjusting Valve Lifter-to-Stem Clearance
Valve refacing reduces clearance
Measuring clearance
Insert valve in guide
Rotate camshaft so lobe is opposite stem
Hold valve against seat
Slide feeler gauge between lifter and stem
Adjust lifter or grind end of valve stem

37. Measuring Valve Clearance

38. Servicing Overhead Valves, Seats, and Guides
Serviced in same way as on L-head engines
Valves cleaned and resurfaced
Seats reconditioned
Measure and recondition guides as needed

39. What parts are measured to check a camshaft for wear
What parts are measured to check a camshaft for wear? The camshaft’s bearing journals, the camshaft bearing bores in the crankcase and cover, and the camshaft lobes.

40. What are the two most common angles for valve faces? 45 and 30

41. How are valve seat inserts secured in their bores? Peening

42. What problems are associated with insufficient valve lifter-to-stem clearance? Advanced valve timing, improper valve seating, burned valves and seats

43. Glossary Interference angle Peening
Difference in angle between mating surfaces of a valve and a valve seat.
Peening
Displacing metal just outside the edge of the valve seat insert to lock the insert in place.

44. Glossary Poppet valves Valve seat width
A valve structure consisting of a circular head with an elongated steam attached in the center.
Valve seat width
The width of the contact area between the valve seat and the valve face.