Cylinder Head Assembly: Testing and Inspection
INSPECTIONValve Guides
Using a micrometer and bore gauge, take diameter readings on valve stems and guides to check stem-to-guide clearance. Be sure to take reading at more than one place along the length of each stem and guide. If clearance exceeds limit, replace valve and valve guide.
Valve Stem Diameter:
Intake:
Standard: 5.465 - 5.480 mm (0.2152 - 0.2157 inch).
Exhaust:
Standard: 5.440 - 5.455 mm (0.2142 - 0.2148 inch).
Valve guide I.D.:
Intake And Exhaust:
Standard: 5.500 - 5.512 mm (0.2166-0.2170 inch).
Stem-to-Guide Clearance:
Exhaust:
Standard: 0.020 - 0.047 mm (0.0008 - 0.0018 inch).
Limit: 0.07 mm (0.0027 inch).
Intake:
Standard: 0.045 - 0.072 mm (0.0018 - 0.0028 inch).
Limit: 0.09 mm (0.0035 inch).
If bore gauge is not available, check end deflection of valve stem with a dial gauge instead. Move stem end in directions (1) and (2) to measure end deflection. If deflection exceeds its limit, replace valve stem and valve guide.
Valve Stem End Deflection Limit:
Intake: 0.14 mm (0.005 inch).
Exhaust: 0.18 mm (0.007 inch).
Valves
^ Remove all carbon from valves.
^ Inspect each valve for wear, burn or distortion at its face and stem and, as necessary, replace it.
^ Measure thickness of valve head. If measured thickness exceeds limit, replace valve.
Valve Head Thickness:
Intake:
Standard: 0.8- 1.2 mm (0.03 - 0.047 inch).
Limit: 0.6 mm (0.024 inch).
Exhaust:
Standard: 0.8- 1.2 mm (0.03 - 0.047 inch).
Limit: 0.7 mm (0.027 inch).
^ Inspect valve stem end face for pitting and wear. If pitting or wear is found there, valve stem end may be resurfaced, but not so much as to grind off its chamfer. When it is worn so much that its chamfer is gone, replace valve.
^ Seating contact width: Create contact pattern on each valve in the usual manner, i.e., by giving uniform coat of marking compound to valve seat and by rotatingly tapping seat with valve head. Valve lapper (tool used in valve lapping) must be used. Pattern produced on seating face of valve must be a continuous ring without any break, and the width of pattern must be within specified range.
Standard Seating Width Revealed By Contact Pattern On Valve Face:
Intake And Exhaust: 1.1- 13 mm (0.0433 - 0.0512 inch).
Valve Seat Repair
A valve seat not producing a uniform contact with its valve or showing width of seating contact that is out of specified range must be repaired by regrinding or by cutting and regrinding and finished by lapping.
1. Exhaust Valve Seat: Use valve seat cutters to make two cuts as illustrated in figure. Two cutters must be used: the first for making 15° angle, and the second for making 45° angle. The second cut must be made to produce desired seat width.
Seat Width For Exhaust Valve Seat: 1.1 -1.3 mm (0.0433 - 0.0512 inch).
2. Intake Valve Seat: Cutting sequence is the same as for exhaust valve seats.
Seat Width For Intake Valve Seat: 1.1-1.3 mm (0.0433 - 0.0512 inch).
3. Valve Lapping: Lap valve on seat in two steps, first with coarse size lapping compound applied to face and the second with fine-size compound, each time using valve lapper according to usual lapping method.
Cylinder Head
^ Remove all carbon from combustion chambers.
NOTE: Do not use any sharp-edged tool to scrape off carbon. Be careful not to scuff or nick metal surfaces when decarboning. The same applies to valves and valve seats, too.
^ Check cylinder head for cracks in intake and exhaust ports, combustion chambers, and head surface.
^ Flatness of gasketed surface: Using a straightedge and thickness gauge, check surface at a total of 6 locations. If distortion limit, given below, is exceeded, correct gasketed surface with a surface plate and abrasive paper of about #400 (Waterproof silicon carbide abrasive paper): place paper on and over surface plate, and rub gasketed surface against paper to grind off high spots. Should this fail to reduce thickness gauge readings to within limit, replace cylinder head. Leakage of combustion gases from this gasketed joint is often due to warped gasketed surface: such leakage results in reduced power output.
Limit Of Distortion: 0.05 mm (0.002 inch)
^ Distortion of manifold seating faces: Check seating faces of cylinder head for manifolds, using a straightedge and thickness gauge, in order to determine whether these faces should be corrected or cylinder head replaced.
Limit of distortion: 0.10 mm (0.004 inch)
Valve Springs
^ Referring to data given below, check to be sure that each spring is in sound condition, free of any evidence of breakage or weakening. Remember, weakened valve springs can cause chatter, not to mention possibility of reducing power output due to gas leakage caused by decreased seating pressure.
Valve Spring Free Length:
Standard: 36.83 mm (1.4500 inch).
Limit: 35.67 mm (1.4043 inch).
Valve Spring Preload;
Standard: 10.7-12.5 kg for 31.5 mm (23.6 - 27.5 lb./1.24 inch)
Limit: 9.3 kg for 31.5 mm (20.5 lbs./1.24 inch)
^ Spring squareness: Use a square and surface plate to check each spring for squareness in terms of clearance between end of valve spring and square. Valve springs found to exhibit a larger clearance than limit given below must be replaced.
Valve Spring Squareness Limit: 2.0 mm (0.079 inch)