1. Engine Diagnosis and Service: Cylinder Head and Valvetrain
Chapter 52

2. Objectives Disassemble a cylinder head in the correct manner
Clean and inspect a cylinder head for cracks and warpage
Diagnose cylinder head and valve train wear problems and determine the correct repair procedure
Understand machine shop repair processes for cylinder heads

3. Objectives (cont’d.) Reassemble a cylinder head
Understand camshaft and cam drive service procedures

4. Introduction Valve job Leaking head gasket
Cylinder head is removed for valve refinishing
Leaking head gasket
Removed for resurfacing and gasket replacement
Timing chain or timing belt service
Important maintenance procedures on today’s long-life engines

5. Head Disassembly and Carbon Removal
Cylinder heads: easier to work on if clean
OHC heads with removable cam caps: verify caps are correctly numbered
Removing valve springs: wear face protection
Keep valves in order
Measure and record valve stem and spring height
Carbon removal
Most OHC heads have oil galleries
Carbon can be removed from necks of valves

6. Cylinder Head Inspection
Cylinder heads sometimes warp
Warped heads are resurfaced
Clean head before checking for flatness
Rock the straightedge so one edge of it rests against the opposite side of the head
A round, straight bar is also available for checking straightness
Warpage
Cast iron head warpage
Aluminium head warpage

7. Resurfacing by Grinding, Cutting, or Sanding
Resurfacing methods
Fly-cutting
Grinding the head
Correct surface finish is very important
Multilayered steel (MLS) gaskets
Require a very smooth surface finish
Head resurfacing
Can increase compression

8. Straightening Cylinder Heads
Warped aluminum OHC heads
Commonly straightened
Several methods for straightening cylinder heads
Best: heating oven
Straighten the head prior to surfacing
Combustion chamber volumes will remain equal

9. Crack Inspection Cracks are sometimes found: Ways to detect cracks
In combustion chambers
Between adjacent combustion chambers
On the valve spring side of the head
Ways to detect cracks
Magnetic crack inspection
Dye penetrant
Pressure testing

10. Crack Repair Cracks are sometimes repairable Cracks in iron heads
Only practical if the cost of a bare head is more than twice the cost of the crack repair
Cracks in iron heads
Repaired with tapered, threaded plugs
Welding heads
Common method of repairing aluminum head cracks

11. Checking Valve Springs
Springs are tested for:
Tension
Squareness
Height
Specifications are available in the service manual

12. Checking Valve Stems Valves wear: oil consumption results
Measure the valve stem with a micrometer

13. Valve Guide Service Valve guides are checked for wear
Wear in a bellmouth fashion
Can result in oil consumption
Valve seat has worn and is wider than usual
Look for a worn valve guide as the cause
Checking valve stem-to-guide clearance
Split ball gauge and micrometer
Dial indicator

14. Guide Repair Guides are repaired in several ways
Worn integral guide bored out to accept a pressed-fit insert guide
Worn insert guide pressed out and replaced with a new one
Knurling
Thinwall insert

15. Grinding Valves
Valves are refinished on face angle using a valve grinder
Stem tip is reground flat
Grinding wheel is dressed with an industrial diamond
Some machinists grind an interference angle
Very little metal is removed from surface of the valve face

16. Grinding Valve Seats
Valve guides must be refinished before refinishing valve seats
Valve seats are refinished with a grinding stone or a seat cutter
45-degree seat angle that mates with valve face is machined until seat area is clean and free of pits
60-degree angle in the bottom of the seat (i.e., throat angle) is cut very lightly
Head must be thoroughly cleaned of all grit before beginning assembly

17. Checking Valve Stem Installed Height
Seat and valve are reground
Stem moves further into the cylinder head
Results in increased valve stem tip height and valve spring installed height
After grinding the valve and seat
Check installed height
Shims may be installed under the springs when a head is reassembled

18. Solvent Testing the Valve and Seat
After the valve and seat have been ground:
Install the spark plugs in their holes
Turn head over so combustion chamber faces up
Place head on head stands and put it on a shelf in solvent tank
Install valves in the ports
Fill the combustion chambers with solvent and check for leaks

19. Reassembling the Head and Valve Guide Seal Installation
Clean head before reassembly
Thoroughly clean the guides
Lubricate all valve stems
Valve guide seal installation
Install guide seals before installing springs on all but O-ring seals
Check instructions in gasket set regarding placement of seals
Lubricate seals before installing them
Positive seals: often supplied with a plastic sheath

20. Install the Valve and Spring Assembly
Some springs have coils more closely spaced at one end than at the other
End more tightly coiled IS positioned against the cylinder head
Compress spring just enough to install keepers
Inspect each keeper for wear
Use grease to help hold keepers in place
Newer engines may use bee hive-shaped springs
One end of coils smaller in diameter

21. Pushrod Engine Rocker Arm Service
Stud-mounted rocker arms
Not serviceable
Replaced when worn
Cast rocker arms that are shaft-mounted
Can be reground
Thoroughly lubricate rocker arms
Before installing

22. Inspect Pushrods and OHC Camshaft
Inspect pushrod ends and surface of socket where it pivots on rocker arm
Look for pitting or other unusual wear
Roll pushrods on a bench to see if they are bent
Overhead camshafts often have oil galleries and holes drilled in cam lobes for direct lubrication
Small oil holes are prone to plugging
Check that oil holes are clear before installing

23. Reassembling OHC Heads
Important steps
Reinstall camshaft in the head
Check to see camshaft cap alignment bushings are installed and positioned correctly
Bucket-type OHC heads
Lubricate buckets and install them in the head prior to installing the cam
Adjust the valve clearance before installing the head on the engine
Valve lash must be enough to allow heat to dissipate from valve to valve seat

24. Camshaft Service Camshaft is inspected for wear
Comparison measurement is made by measuring each lobe
Visual check of cam lobes for wear is standard
Lobes on roller cams are polished to fine matte finish
During engine break-in, the lifter burnishes the lobe to a smooth mirror finish

25. Lifter Service and Cam and Lifter Break-in
Hydraulic lifters fail for several reasons
Dirt lodged in the check valve
Oil pressure problem
Varnish accumulates between plunger and body
Hydraulic lifters are not rebuilt
Relatively inexpensive
Worn mechanical lifters can be reground
Lubrication and break-in are critical
Cam that survives the first half hour of use without wear should last the life of the vehicle

26. Timing Chain and Belt Service
Camshafts on modern engines
Driven by belt and chain
Some older engines used two gears between the crankshaft and camshaft

27. Timing Belt Service Increased timing belt fabric wear causes
Poor alignment
Incorrect tension
Worn sprockets
Inspect condition
Twist belt gently
Belt life
Affected by contact with foreign materials

28. Timing Belt Replacement
Follow manufacturer's recommendations for belt replacement interval
Most American cars are free-wheeling
Most replacements take three- to four-hours
Install new belt and adjust belt tension until snug
Do not adjust timing belt tension on a hot engine
Affix a sticker to fender that tells the mileage when timing belt service was done

29. Timing Chain Service Excessive chain stretch
Checked in different ways
Long chains like those used on OHC engines always use chain tensioners
Ways to time the cam to the crank
Some timing sprockets are properly timed when the marks face each other
Some require a certain number of chain links between marks
Some have colored links that must be aligned