Cylinder Head Service Flashcards
What are the 3 stages of removing valve operating mechanism?
- Loosen all adjusters to eliminate load.
- Unbolt and remove rocker shaft assemblies, keeping in order.
- Remove pushrods, keeping in order
Before head is removed what should be done with fuel system?
Remove injectors. If head has integral fuel passages, drain the fuel from the passages before removing injectors
How should head fasteners be removed?
Sequentially to relieve stress evenly starting from the outside and working in
How should a head be stored?
On wooden blocks to protect machined surfaces
When measuring deck surfaces make sure to stay away from?
Valve seats and inserts
Bolt holes
Water holes
Oil holes
Intake and exhaust manifold surfaces should be measured for?
Flatness using straight edge and feeler blade
Water passages should be inspected for?
signs of scale and deposits. White scale- high minerals in water. Green/blue- high SCA’s. Rust or corrosion- Low SCA’s
Valve guide bore inspection?
Should have carbon removed. Check guide for signs of scoring and signs of uneven wear.
Valves should be visually inspected for?
Face for smooth surface with not cracks or nicks
Head for cracks, corrosion or burring
Stem for galling, scoring, wear, necking, or marks in fillet
Tip is not mushroomed, chipped or missing chamfer
What are two common valve face angle used?
30* , often used on intake - has better airflow characteristics.
45*, often used on exhaust valves as it creates more seating force
Before a valve can be ground what must be done?
Checked for runout
When grinding a valve, what must be checked in relation to margin?
Margin must be at least half of that of a new one.
What will happen to a valve with insufficient valve margin?
run excessively hot and burn prematurely
What is usually done to compensate for lost material when head is resurfaced?
Most manufactures supply thicker head gaskets
What are the ways that integral valve guides are serviced?
Knurling - only a temporary repair. Metal is expanded and then reamed to correct size
Repair sleeve - boring out guide and installing a sleeve or insert
What two problems can result from incorrect valve guide height?
Too high - retainer making contact with valve guide
Too low - contact between guide and fillet causing valve to not seat properly
What reasons would warrant replacement of valve seat inserts?
Seat area is excessively worn
inserts are loose in head
The head is cracked next to inset
When grinding for a interference angle, which angle must be larger?
Valve seat angle
Three basic operations of grinding a valve seat
- Grind seat to correct angle
- Use a 15* stone to lower upper edge of seat
- use 60-70* stone to narrow the seat to the correct width
Valve head height or protrusion
The distance between the bottom of the valve head to the machined gasket surface on the head
Excessive valve height causes
an increase in compression ratio, possibility of valve contacting piston
Insufficient valve height causes
Reduction in compression ratio
What 4 things should be checked for when inspecting cylinder head cap screws
Damaged or missing threads
Corrosion or pitting
Reduced diameter
Stretch
What effect would worn valve guides have on a running engine?
Worn guides prevent proper sealing, causing leakage during the compression and power strokes resulting in a loss of power. Can also cause an increase in oil consumption
When inspecting head where must you pay close attention to for cracks?
Between injector holes and valve seats
Valve spring free length
The total length of spring free standing uncompressed
Valve springs should be checked for?
Nicks, cracks, corrosion, that they are square and that tension is still within specifications
Low valve spring tension can cause?
Poor valve sealing
Poor valve cooling
Valve float or flutter
What is maximum allowable variation for valve spring squareness?
1/16”
If a rocker arm shaft support is cracked or shows signs of damage what should be done with them?
Replaced
Ends of pushrods should be inspected for?
Wear, overheating, galling, fatigue, pushed in inserts are tight
3 factors that can cause a permanently bent pushrod
Fatigue
Mechanical failure
Service problem
What must be done with pushrods that are bent?
Replaced
General rule for shims placed under valve springs
No more then two totalling in a total thickness of 0.060”
What is procedure for testing valve sealing?
using vacuum tester, apply vacuum of 20 in of Hg, any more then 10 in loss in ten seconds is considered to be excessive
In order to adjust valve lash, the valves must be in what position?
Closed
Worn rocker arms, shafts and crossheads would most likely cause?
Excessive valve train noise
Over compressing the valve spring during assembly could cause?
Damage to the valve seal
Why are valve lash adjustment necessary?
To provide clearance for component expansion during heating of engine operation, compensate for wear in the valve operating mechanism
