Cylinder Head Assembly: Service and Repair
CYLINDER HEAD AND VALVESRemoval
Follow removal steps outlined in illustration.
1. Remove cylinder head bolts.
2. With cylinder head removed, compress valve springs using Special Tool MD998772A and 6779 or equivalent.
3. Remove valve retaining locks, valve spring retainers and valve spring.
4. Remove valve stem seal/valve spring seat by using Special Tool C-4745 or equivalent.
5. Before removing valves, remove any burrs from valve stem lock grooves to prevent damage to the valve guides. Identify valves to insure installation in original location.
Cleaning
Cylinder Head
CAUTION: Be careful not to gouge or scratch the aluminum head sealing surface.
1. Remove all gasket material from cylinder head and block.
Valve Assembly
1. Clean all valve guides, valves and valve spring assemblies thoroughly with suitable cleaning solution before reassembling.
Inspection
Cylinder Head
1. Check the cylinder head gasket surface for flatness by using a straightedge and feeler gauge.
Limit: 0.1 mm (0.004 inch)
Valve
1. Clean valves thoroughly and discard burned, warped and cracked valves.
2. Measure valve stems for wear.
3. If valve stems are worn more than 0.05 mm (0.002 inch), replace valve.
Standard value:
Intake 5.934 - 5.952 mm (0.2336 - 0.2343 inch)
Exhaust 5.906 - 5.924 mm (0.2325 - 0.2332 inch)
Valve Guides
1. Remove carbon and varnish deposits from inside of valve guides with a reliable guide cleaner.
2. Using a small hole gauge and a micrometer, measure valve guides in 3 places top, middle and bottom. Replace guides if they are not within specification.
Standard value:
Intake 0.023 - 0.066 mm (0.0009 - 0.0025 inch)
Exhaust 0.051 - 0.094 mm (0.0020 - 0.0037 inch)
Limit: 0.25 mm (0.010 inch)
3. Install the valve guide until it projects 13.25 - 13.75 mm (0.522 - 0.541 inch) from the cylinder head as illustrated.
Testing Valve Springs
1. Whenever valves have been removed for inspection, reconditioning or replacement, valve springs should be tested. As an example, the compression length of the spring to be tested is 33.34 mm (1.313 inch).
Turn table of Tool C-647 until surface is in line with the 33.34 mm (1.313 inch) mark on the threaded stud and the zero mark on the front. Place spring over stud on the table and lift compressing lever to set tone device. Pull on torque wrench until ping is heard. Take reading on torque wrench at this instant. Multiply this reading by two. This will give the spring load at test length. Fractional measurements are indicated on the table for finer adjustments. Refer to specifications to obtain specified height and allowable tensions. Discard the springs that do not meet specifications.
Standard value:
Free length 46 mm (1.811 inch)
Spring tension
Valve closed
246 - 270 N/38.0 mm (50 - 60 lbs./1.496 inch)
Valve open
459 - 611 N/29.3 mm (123 - 137 lbs./1.153 inch)
2. Inspect each valve spring for squareness with a steel square and surface plate, test springs from both ends. If the spring is more than 1.5 mm (0.06 inch) out of square, install a new spring.
Refacing Valves And Valve Seats
1. The intake and exhaust valve seats and valve face have a 45 degree angle.
2. Inspect the remaining margin after the valves are refaced. Exhaust valves with less than 0.95 mm (0.0037 inch) margin and intake valves with less than 1.05 mm (0.0413 inch) margin should be discarded and replaced.
3. When refacing valve seats, it is important that the correct size valve guide pilot be used for reseating stones. A true and complete surface must be obtained.
4. Measure the concentricity of valve seat using a valve seat dial indicator. It should not exceed circular runout.
Limit: 0.05 mm (0.002 inch) Indicator reading
5. Inspect the valve seat with Prussian blue to determine where the valve contacts the seat.
To do this, coat valve face LIGHTLY with Prussian blue then set valve in place. Rotate the valve with light pressure. If the blue is transferred to the center of valve face, contact is satisfactory. If the blue is transferred to top edge of the valve face, lower valve seat with a 15 degree stone. If the blue is transferred to the bottom edge of valve face raise valve seat with a 65 degree stone.
Valve seats which are worn or burned can be reworked if correct angle and seat width are maintained. Otherwise, cylinder head must be replaced.
6. When seat is properly positioned, the width of intake and exhaust seats should be 0.9 to 1.3 mm (0.035 to 0.051 inch).
7. Check valve tip to spring seat dimensions A after grinding the valve seats or faces. Grind valve tip until dimension A is equal to 47.99 mm (1.889 inch) for exhaust valve and 48.04 mm (1.891 inch) for intake valve over spring seat when installed in the head.
The valve tip chamfer may need to be reground to prevent seal damage when the valve is installed.
8. Check the valve spring installed height B after refacing the valve and seat. Make sure measurements are taken from top of spring seat to the bottom surface of spring retainer.
If height is greater than 38.00 mm (1.496 inch), install a 0.762 mm (0.030 inch) spacer in head counterbore under the valve spring seat to bring spring height back within specification.
Installation
Installation in reverse order as removal.
1. Coat valve stems with clean engine oil and insert them in cylinder head.
2. If valves or seats have been reground, check valve tip height (A).
Make sure measurements from cylinder head surface to the top of valve stem.
3. Install valve seal/spring seat assembly over valve guides on all valve stems. Ensure that the garter spring is intact around the top of the rubber seal. Install valve springs, valve retainers.
4. Compress valve springs with a valve spring compressor install locks and release tool.
Cylinder head bolts should be carefully examined BEFORE reuse. If the threads are necked down the bolts should be replaced.
Necking can be checked by holding a scale or straight edge against the threads. If all the threads do not contact the scale the bolt should be replaced.
5. Before installing the bolts the threads should be oiled with clean engine oil.
6. Tighten the cylinder head bolts in the sequence shown in the figure.
Using the 4 step torque turn method, tighten according to the following values:
Without Multi layer Steel Head Gasket
Step 1
Tighten center fasteners 1 thru 6 to 33 Nm (25 ft. lbs.).
Then outer fasteners 7 thru 10 to 27 Nm (20 ft. lbs.)
Step 2
Tighten center fasteners 1 thru 6 to 67 Nm (50 ft. lbs.).
Then outer fasteners 7 thru 10 to 27 Nm (20 ft. lbs.).
Step 3
Tighten center fasteners 1 thru 6 to 67 Nm (50 ft. lbs.).
Then outer fasteners 7 thru 10 to 27 Nm (20 ft. lbs.).
Step 4
Turn all fasteners 1 thru 10 1/4 turn (90 degrees). Do not use a torque wrench for this step.
With Multi Layer Steel Head Gasket
Note: The four short bolts are placed in the corners.
Step 1
Torque all center bolts to 34 Nm (25 Ft Lbs), Torque the 4 corner bolt to 27 Nm (20 Ft Lbs)
Step 2
Torque all center bolts to 68 Nm (50 Ft Lbs), Torque the four corner bolts to 47 Nm (35 Ft Lbs),
Step 3
Re-torque all center bolts to 68 Nm (50 Ft Lbs), Re-torque the 4 corner bolts to 47 Nm (35 Ft Lbs).