Bold reference numbers in this section identify parts not shown in the figures alongside the text, but which can be found in the exploded view diagram.

On disassembly of the components mounted on the cylinder head it is essential that they are laid out or marked in such a way that they can be refitted in exactly the same position they occupied before being removed.

Using tool 88713.2096, unscrew the nuts (19) on the cylinder head studs.

Fit the socket of service tool no. 88713.1805 on the camshaft nut then rotate the camshaft to release the opening rocker arm (3).

Remove the camshaft (Sect. N 4.3, Removal of the camshafts).

Slide the valve closing shim (8) along the intake valve stem (17) in such a way as to make it possible to remove the two half rings (7) securing the valve.

Attach the end of the spring (9) of the closing rocker arm (18) to the tool 88713.2916.

Remove the rocker arm (18), the spring (9) and service tool no. 88713.2916.

The cylinder barrel mating surface must be perfectly flat. If this is not the case, spread diamond dressing compound (6 to 12 micron thickness) on a reference surface and slide the cylinder head on the surface as shown in the figure until a flat finish is obtained.

Check that the stem and the valve seat contact surface are in good condition. There must be no pitting, cracks, deformations or signs of wear.

Perform the following checks: measure the diameter of the valve stem (B) at various heights along the portion that runs in the valve guide.

Check that valve head band (at 45° to valve head top face) is concentric to the valve stem as follows: place the valve on a V block, set a dial gauge at right angles to the head and rotate the valve.

0.03 mm.

If a valve seat is only slightly damaged, it may be lapped using the special 45° lapping tools, with subsequent bedding of the valve into the seat.

If the valve seats are excessively damaged, fit oversize seats. Replacement seats are available with 0.03 and 0.06 mm oversized outside diameters.

Check the diameter of head bores and choose the oversized valve seat that will give an interference fit of 0.11 to 0.16 mm.
Replacement valve seats are supplied in outside diameter oversizes of 0.03 and 0.06 mm.

Heat the cylinder head gradually and evenly up to 200 °C and chill the new valve seats in dry ice.

Use Prussian blue or a mixture of minimum and oil to check that the contact surface (W) between valve and seat is 1.0 to 1.5 mm.

2.0 mm.

Carefully examine the internal surface of the valve guide: for cracking or distortion. If the guide is excessively out-of-round, use a reaming tool to make the mating faces more uniform.

0.03 to 0.06 mm.

0.08 mm.

Heat up the cylinder head gradually and evenly up to 200 °C.

Select the most suitable replacement valve guide to obtain an interference fit in the cylinder head bore of 0.022-0.051 mm;
replacement valve guides are supplied in O.D. oversizes of 0.03, 0.06 and 0.09 mm complete with lock rings.

Lubricate the seat and install the valve guide so that the stop ring is located against the head, using the drift previously used to remove the old guide.

10.040 to 10.062 mm.

10.005 mm.

The assembly clearance must be 0.03 to 0.06 mm.

0.08 mm.

In the event of excessive clearance, fit 0.02 mm oversize shafts (available from Parts Service).

To refit the cylinder head reverse the steps of the removal procedure; pay particular attention to those operations mentioned specifically.

If removed, fit new valve guide seal rings (10), lubricate with engine oil and insert from the spring side with tool part no. 88713.2442.

Fit the closing rocker arm (18) and relative spring (9) on service tool no. 88713.2916.

Insert the rocker shaft (4) with a new O-ring (22) (apply grease to the O-ring).

Fit the assembly made up of tool no. 88713.2916, rocker arm and spring to cylinder head and shaft (4).

Detach the spring (9) and remove the tool 88713.2916.

Reposition the screwdriver, and compress the spring as much as possible while holding the valve, the shim and the half rings in the valve closed position. Release the closing rocker (18) with a rapid motion, so that the half rings seat in the shim.

With the valve in rest position and while pushing on the rocker arm to oppose the force of the return spring, check that the clear­ance between the rocker shoe and the closing shim is within the specified tolerance limits (Sect. N 4.1, Checking the closing clearance (Sc) of the intake/exhaust valves). If not, adjust the valve clearance (Sect. N 4.1, Checking and adjusting valve clearanc­es).

Once the required clearance is obtained, take out the camshaft that was temporarily installed, lubricate it using graphite oil and refit it onto the head.

With the valve in rest position, check that clearance between the rocker arm (3) and the shim (6) is within the specified tolerance limits (Sect. N 4.1, Checking the opening clearance (Sa) of the intake/exhaust valves).

If not, adjust the valve clearance as described under Sect. N 4.1, Checking and adjusting valve clearances.

Follow the same procedure to fit the intake valve (16).

To prevent oil leaks past the contact area between cylinders and crankcase, each time the head is removed, cylinder and piston must be removed as well to clean the mating faces of crankcase and cylinder and restore the spoiled gaskets and O-rings and apply again liquid sealant (Sect. N 5, Refitting the cylinder/piston assembly).

Before refitting the cylinder head assemblies, fit new head gaskets (12) and check that the locating dowels (A) and bushings (B) are installed (Sect. N 5, Cylinder/piston assemblies).

Fit the special washers (20) over the stud bolts (P) with the square edged face towards the cylinder head and the flat face towards the inside.

Using tool no. 88713.2096 in conjunction with a torque wrench, gradually tighten the cylinder head nuts to the specified torque in a crosswise sequence (Sect. C 3, Engine torque settings).