Mazda MX-5 NA silhouetteMX-5 NA

INSPECTION / REPAIR

B-49prose procedure
Continued from B-48

Cylinder head — manifold contact surface

  1. 4
    Measure the manifold contact surface distortion in the four directions shown in the figure.
    Cylinder head shown end-on with the intake/exhaust manifold mating face highlighted; arrows indicate the four directions in which manifold-contact-surface distortion is measured with a straight edge and feeler gauge.
    05U0BX-289
  2. 5
    If distortion exceeds specification, grind the surface or replace the cylinder head.
DistortionManifold contact surface
0.15mm (0.006 in) max

VALVE MECHANISM

Valve and valve guide

  1. 1
    Inspect each valve for the following. Replace or resurface the valve if necessary. (1) Damaged or bent stem. (2) Rough or damaged face. (3) Damaged or unevenly worn stem tip.
    Valve nomenclature diagram — single valve drawn with labels for STEM TIP (top), VALVE FACE (mid), MARGIN THICKNESS (head edge), and VALVE FACE ANGLE = 45° at the seating face.
    05U0BX-122
  2. 2
    Measure the valve head margin thickness of each valve. Replace the valve if necessary.
  3. 3
    Measure the length of each valve at the points shown.
    Measuring valve length with an outside micrometer on the valve overall length (tip to head).
    05U0BX-123
  4. 4
    Measure the stem diameter of each valve.
    Measuring valve stem diameter with a micrometer; inset shows the stem cross-section with the measurement axis indicated by a cross-hair.
    05U0BX-124
  5. 5
    Measure the inner diameter of each valve guide at the points shown.
  6. 6
    Calculate the valve stem to guide clearance. Subtract the outer diameter of the valve stem from the inner diameter of the corresponding valve guide.
    Valve-to-guide clearance diagram — cross-section of the valve guide bore with the valve stem inside it, labels for VALVE STEM, VALVE GUIDE, and CLEARANCE between the two.
    05U0BX-125
  7. 7
    If the clearance exceeds specification, replace the valve and/or valve guide.
Margin thickness INIntake valve
1.0mm (0.039 in)
Margin thickness EXExhaust valve
1.0mm (0.039 in)
Length — Standard INIntake valve
105.29mm (4.1452 in)
Length — Standard EXExhaust valve
105.39mm (4.1492 in)
Length — Minimum INIntake valve
104.79mm (4.1256 in)
Length — Minimum EXExhaust valve
104.89mm (4.1295 in)
Stem diameter INIntake valve
5.970—5.985mm (0.2350—0.2356 in)
Stem diameter EXExhaust valve
5.965—5.980mm (0.2348—0.2354 in)
Valve guide inner diameter INIntake
6.01—6.03mm (0.2366—0.2374 in)
Valve guide inner diameter EXExhaust
6.01—6.03mm (0.2366—0.2374 in)
Stem-to-guide clearance INIntake
0.025—0.060mm (0.0010—0.0024 in)
Stem-to-guide clearance EXExhaust
0.030—0.065mm (0.0012—0.0026 in)
Stem-to-guide clearance MaximumWear limit
0.20mm (0.008 in)
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