A25A-FKS (ENGINE MECHANICAL): CYLINDER HEAD: INSPECTION; 2021 - 2022 MY Avalon [08/2020

Last Modified: 08-21-2023	6.11:8.1.0	Doc ID: RM100000001Q5AO
Model Year Start: 2021	Model: Avalon	Prod Date Range: [08/2020 - ]
Title: A25A-FKS (ENGINE MECHANICAL): CYLINDER HEAD: INSPECTION; 2021 - 2022 MY Avalon [08/2020 - ]

INSPECTION

PROCEDURE

1. INSPECT CYLINDER HEAD SUB-ASSEMBLY

(a) Using a precision straightedge and feeler gauge, measure the warpage of the contact surfaces where the cylinder head sub-assembly contacts the cylinder block sub-assembly, intake manifold and exhaust manifold (TWC: Front Catalyst).

*a	Bottom Side	*b	Intake Manifold Side
*c	Exhaust Manifold (TWC: Front Catalyst) Side	-	-

Maximum Warpage:

Item	Specified Condition
Bottom side	0.05 mm (0.00197 in.)
Intake manifold side	0.10 mm (0.00394 in.)
Exhaust manifold (TWC: Front Catalyst) side	0.10 mm (0.00394 in.)

HINT:

If the warpage is more than the maximum, replace the cylinder head sub-assembly.

(b) Using a dye penetrant, check the intake ports, exhaust ports and cylinder head sub-assembly surface for cracks.

HINT:

If cracks are found, replace the cylinder head sub-assembly.

2. INSPECT COMPRESSION SPRING

(a) Intake Side:

(1) Using a vernier caliper, measure the free length of the compression spring.

Standard Free Length:

53.71 mm (2.11 in.)

HINT:

If the free length is not as specified, replace the compression spring.

(2) Using a steel square, measure the deviation of the compression spring.

Maximum Deviation (Reference):

1.0 mm (0.0394 in.)

HINT:

If the deviation is more than the maximum, replace the compression spring.

*a	Deviation
*b	37 mm (1.46 in.)

(b) Exhaust Side:

(1) Using a vernier caliper, measure the free length of the compression spring.

Standard Free Length:

55.11 mm (2.17 in.)

HINT:

If the free length is not as specified, replace the compression spring.

(2) Using a steel square, measure the deviation of the compression spring.

Maximum Deviation (Reference):

1.0 mm (0.0394 in.)

HINT:

If the deviation is more than the maximum, replace the compression spring.

*a	Deviation
*b	38 mm (1.50 in.)

3. INSPECT INTAKE VALVE

(a) Using a micrometer, measure the diameter of the intake valve stem.

Standard Valve Stem Diameter:

5.470 to 5.485 mm (0.215 to 0.216 in.)

HINT:

If the valve stem diameter is not as specified, check the intake valve guide bush oil clearance.

(b) Using a vernier caliper, measure the intake valve head margin thickness.

Standard Margin Thickness:

1.0 mm (0.0394 in.)

Minimum Margin Thickness:

0.5 mm (0.0197 in.)

HINT:

If the margin thickness is less than the minimum, replace the intake valve.

*a	Margin Thickness

Standard Overall Length:

104.45 mm (4.11 in.)

Minimum Overall Length:

103.95 mm (4.09 in.)

HINT:

If the overall length is less than the minimum, replace the intake valve.

*a	Overall Length

4. INSPECT EXHAUST VALVE

(a) Using a micrometer, measure the diameter of the exhaust valve stem.

Standard Valve Stem Diameter:

5.465 to 5.480 mm (0.215 to 0.216 in.)

HINT:

If the valve stem diameter is not as specified, check the exhaust valve guide bush oil clearance.

(b) Using a vernier caliper, measure the exhaust valve head margin thickness.

Standard Margin Thickness:

1.0 mm (0.0394 in.)

Minimum Margin Thickness:

0.5 mm (0.0197 in.)

HINT:

If the margin thickness is less than the minimum, replace the exhaust valve.

*a	Margin Thickness

Standard Overall Length:

108.7 mm (4.28 in.)

Minimum Overall Length:

108.2 mm (4.26 in.)

HINT:

If the overall length is less than the minimum, replace the exhaust valve.

*a	Overall Length

5. INSPECT VALVE GUIDE BUSH OIL CLEARANCE

(a) Using a caliper gauge, measure the inside diameter of the valve guide bush.

Standard Valve Guide Bush Inside Diameter:

5.51 to 5.53 mm (0.217 to 0.218 in.)

(b) Subtract the valve stem diameter measurement from the valve guide bush inside diameter measurement.

Standard Oil Clearance:

Item	Specified Condition
Intake Side	0.025 to 0.060 mm (0.000984 to 0.00236 in.)
Exhaust Side	0.030 to 0.065 mm (0.00118 to 0.00256 in.)

Maximum Oil Clearance:

Item	Specified Condition
Intake Side	0.080 mm (0.00315 in.)
Exhaust Side	0.10 mm (0.00394 in.)

HINT:

Oil clearance = Valve guide bush inside diameter - Valve stem diameter
If the oil clearance is more than the maximum, replace the valve and valve guide bush.

6. INSPECT INTAKE VALVE SEAT

(a) Apply a light coat of Prussian blue to the valve face.

(b) Lightly press the valve face against the intake valve seat.

NOTICE:

Do not rotate the valve while pressing it.

Width

(1) If Prussian blue appears 360° around the entire intake valve face, the valve face is concentric.

HINT:

If the valve face is not concentric, replace the intake valve.

(2) If Prussian blue appears 360° around the entire intake valve seat, the intake valve seat and valve face are concentric.

HINT:

If the valve face is not concentric, replace the cylinder head sub-assembly.

(3) Measure the width of the contact area of the intake valve seat and valve face.

Standard Width:

1.0 to 1.4 mm (0.0394 to 0.0551 in.)

7. INSPECT EXHAUST VALVE SEAT

(a) Apply a light coat of Prussian blue to the valve face.

(b) Lightly press the valve face against the exhaust valve seat.

NOTICE:

Do not rotate the valve while pressing it.

Width

(1) If Prussian blue appears 360° around the entire exhaust valve face, the valve face is concentric.

HINT:

If the valve face is not concentric, replace the exhaust valve.

(2) If Prussian blue appears 360° around the entire exhaust valve seat, the exhaust valve seat and valve face are concentric.

HINT:

If the valve face is not concentric, resurface the exhaust valve seat.

(3) Measure the width of the contact area of the exhaust valve seat and valve face.

Standard Width:

1.3 to 1.7 mm (0.0512 to 0.0669 in.)

8. INSPECT CAMSHAFT THRUST CLEARANCE

(a) Clean the No. 1 camshaft bearing cap, No. 2 camshaft bearing cap, 2 No. 3 camshaft bearing caps, No. 4 camshaft bearing cap, camshaft housing sub-assembly and camshaft journals.

(b) Place the camshaft and No. 2 camshaft on the camshaft housing sub-assembly on the cylinder head sub-assembly.

Click here

(d) Install the camshaft housing sub-assembly.

Click here

(e) Using a dial indicator, measure the thrust clearance while moving the camshaft and No. 2 camshaft back and forth.

Standard Thrust Clearance:

Item	Specified Condition
Camshaft	0.04 to 0.17 mm (0.00157 to 0.00669 in.)
No. 2 Camshaft	0.04 to 0.17 mm (0.00157 to 0.00669 in.)

Maximum Thrust Clearance:

Item	Specified Condition
Camshaft	0.22 mm (0.00866 in.)
No. 2 Camshaft	0.22 mm (0.00866 in.)

HINT:

If the thrust clearance is more than the maximum, replace the camshaft housing sub-assembly. If the thrust surface is damaged, replace the camshaft or No. 2 camshaft.