S46, S56, S66, RB75 +4X4

Phaser Engine Sections 12A-12 /13

Cylinder head assembly

Continued From

Cylinder head
To inspect and to correct 12A-12

1 Remove the cylinder head assembly, operation 12A-07.

2 Remove the thermostat housing.

3 Inspect the cylinder head for signs of gas or coolant leakage.

4 Remove the valve springs and the valves. operation 12A-08.

5 Clean the face of the cylinder head and the passages for coolant and for lubricating oil. The water jacket can be cleaned with a special solvent which must be used in accordance with the manufacturer's instructions.

6 Test the cylinder head for leaks.

7 When the cylinder head is thoroughly clean, check it for cracks. Examine carefully the areas around the valve seats and around the holes for the atomiser nozzles.

8 The bottom face of the cylinder head can be machined if: there is distortion, see paragraph 9; there are deep scratches; or, for engines types AA, AC, YA, and YC, the valve depths are below the service limit.

9 Use a straight edge and feeler gauges to check the cylinder head for distortion across and along its bottom face. see section 11 C.

If the distortion is more than the limit given in section 11 C, the bottom face can be machined. Remove only the minimum material and ensure that the thickness of the cylinder head will not be less than 120,48 mm (4.035 in) after the cylinder head has been machined.

Attention: After the cylinder head has been machined the valve seats must be corrected to give the correct valve head depth. It is advisable to work to the minimum limit to allow for later wear.

10 Check the valve seats for wear and for damage.

11 Before any work is done on the valve seats, ensure that there is no wear on the valve guides. see section 11 C. If the valve guide wear is more than the limit, then the valve guide must be renewed, operation 12A-11.

12 Where there is little damage, the valve and valve seat can be lapped. When the valve seats are lapped keep the seat as narrow as possible and ensure that all the compound used to lap the valve and the seat is removed.

13 More badly damaged valve seats can be corrected by use of the cutter tool, operation 12A-13, or new inserts can be fitted, operation 12A-14.

To correct a valve seat
with a valve seat cutter 12A-13
Special tools:

Cutter for inlet valve seats, MS.281 *
Cutter for exhaust valve seats, MS.275*
Pilot for use with valve seat cutters, MS. 150-9.5* Handle set for use with valve seat cutters, MS.67B*
* Included in set of adjustable cutters for valve seats, MS.73A

1 If the valve guide is worn, renew it, operation 12A-11.

2 Fit the pilot in the valve guide and tighten the pilot.

3 Select the relevant cutter. Set the cutters to the diameter of the valve seat to be cut. Fit the cutter on the pilot and fit the handle (A). Ensure that the cutter is not allowed to fall on to the seat as this can damage the blades.

4 Carefully turn the cutter in a clockwise direction. Remove only the minimum material to ensure a good seat. Keep the seat as narrow as possible.

5 When the seat is cut, remove the cutter and the pilot. Remove any debris from the area of the valve seat and the port.

6 Fit the valve and lightly lap the valve and the seat.

7 Check that the valve depth is within limits, see section 11C.
If a valve seat has become too damaged or too worn, a valve seat insert can be fitted to engines types AA, AC, YA and YC. Engines types AB, AD, YB and YD have valve seat inserts fitted as standard and these inserts can be renewed.