4.4 - | Cylinder head assemblies: valves - rocker arms

Vertical cylinder head
HORIZONTAL CYLINDER HEAD

1 | Clip

2 | Shim

3 | Opening rocker arm

4 | Rocker arm shaft

5 | O-ring

6 | Valve opening shim

7 | Half rings

8 | Valve closing shim

9 | Spring

10 | Valve rubber

11 | Exhaust valve guide

12 | Washer

13 | Intake valve guide

14 | Intake valve seat

15 | Exhaust valve seat

16 | Exhaust valve

17 | Intake valve

18 | Closing rocker arm

19 | Nut

Parts catalogue

Crankcase halves
Vertical cylinder head
HORIZONTAL CYLINDER HEAD

Important
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.
Removal of the cylinder head assembly

Operation | Section reference
Remove the engine from the frame | N 1, Removal of the engine
Remove the timing belt covers and the timing belts | N 4.2, Removal of the timing belt covers

Removal of the cylinder heads
Notes
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 88713.2676, unscrew the nuts (19) on the cylinder head studs.
Remove the nuts (19) and recover the special washers (12) positioned between the nuts and the cylinder head.
Remove the head assembly from the engine by lifting it off the engine stud bolts.
Remove the cylinder head gaskets (C).
Removal of the rocker arms, shims and valves

Operation | Section reference
Remove the valve covers | N 4.3, Removal of the valve covers
Remove the camshaft end caps | N 4.3, Removal of the inner timing belt covers

Remove the clip (1) securing the opening rocker (3).
Move the rocker arm (3) to free the valve opening shim (6).
Screw service tool 88713.2837 to the threaded end of the opening rocker shaft (4).
Withdraw the rocker shaft (4) and recover the opening rocker arm (3) and the two shims (2).
Remove the camshaft (Sect. N 4.3, Removal of the camshafts).
Using two screwdrivers, hold the closing rocker arm (18) in the “valve open” position.
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.
Use long nosed pliers or a magnetic screwdriver to remove the half rings (7) from the valve stem.
Slide the valve closing shim (8) off the valve (17).
Withdraw the valve (17) from the underside of the cylinder head.
Repeat the above operations for the exhaust side.
Attach the end of the spring (9) of the closing rocker arm (18) to the tool 88713.2783.
Remove the closing rocker arm shaft (4) using service tool 88713.2837.
Remove the rocker arm (18), the spring (9) and service tool 88713.2783.
Overhaul of cylinder head components
Overhaul of the cylinder heads
Remove any carbon deposits from the combustion chamber and its ducts.
Check for cracking and inspect the sealing surfaces for scoring, ridges or other damage.
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.
Checking the valves
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.
Warning
The valves cannot be ground.
Perform the following checks: measure the diameter of the valve stem (D) 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.
- Service limit: 0.03 mm.
Checking the valve seats
Visually inspect the valve seats: there must no excessive hollowing and there must be no pitting or cracks.
If a valve seat is only slightly damaged, it may be lapped using the special 45° lapping tools, with subsequent grinding of the valve into its seats.
If the valve seats are excessively damaged, fit oversize seats. Replacement seats are available with 0.03 and 0.06 mm oversized outside diameters.
Important
When you change the valve seats, change the valve guides as well.
Renewal of the valve seat
Remove the worn seats by grinding out the rings. Take great care not to damage the valve seat housing in the cylinder head.
Check the diameter of cylinder 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.
Install the seats perfectly square into their bores using a suitable installer.
Allow to cool and then lap the valve seats, smooth the connections between the ducts and the new seats and grind the valves.
Valve–seat contact surfaces
Use Prussian blue or a mixture of minium and oil to check that the contact surface (W) between valve and seat is 1.0 to 1.5 mm.
Maximum permissible limit:
2.0 mm.
Grind the seat if the dimension measured is greater than above limit.
Fill the intake and exhaust ducts with fuel to check for leaks; if leaking occurs, check the sealing surfaces for burrs.
Overhaul of the valve guides
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.
Notes
When you change the valve guide, you must also change the valve. The intake valve guides are made from cast iron, whereas the exhaust valve guides are bronze.
Valve-valve guide clearance
Assembly clearance:
0.03 to 0.06 mm.
Maximum permissible wear limit:
0.08 mm.
Renewal of the valve guides
To renew the valve guides (11) and (13), proceed as follows.
Heat up the cylinder head gradually and evenly up to 200 °C.
Drive out the valve guide using a suitable drift (see drawing).
Allow the cylinder head to cool down and check the condition of the seat.
Select the most suitable replacement valve guide to obtain an interference fit in the cylinder head bore of 0.022 to 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.
Heat up the cylinder head again and chill the new valve guide in dry ice.
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.
Allow the cylinder head to cool, then ream out the inside of the new valve guide.
Overhauling the rocker arms
Check for signs of wear, grooves or chrome flaking off.
Check the condition of the rocker arm bore and shaft.
nominal diameter of rocker arm bore:
10.040 to 10.062 mm.
nominal diameter of rocker arm shaft:
10.001 to 10.010 mm.
Check the contact surfaces of the shims and the valve return collets are perfectly flat with no signs of wear.
Rocker shaft–rocker bore clearance
The assembly clearance must be 0.03 to 0.06 mm.
Maximum permissible wear limit:
0.08 mm.
The rocker arm shafts should be a light force fit in the cylinder head.
In the event of excessive clearance, fit 0.02 mm oversize shafts (available from Parts Service).
Checking the rocker arm springs
Carefully examine the springs (9) of the closing rocker arms (18). There must be no signs of cracking, distortion, or loss of elasticity.
Refitting the cylinder head assembly
To refit the cylinder head reverse the steps of the removal procedure; pay particular attention to those operations mentioned specifically.
It is very important that all the components are carefully cleaned.
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 end of the tool into the valve guide and use a mallet to tap the seal rings (10) home into the valve guides.
Refitting the rocker arms, shims and valves
Fit the closing rocker arm (18) and relative spring (9) on service tool no. 88713.2783.
Insstall the service tool – rocker arm –spring assembly in the cylinder head and insert the shaft (4) with a new seal ring (5), suitably lubricated.
Important
When assembling the rocker arm shafts (4) make sure that threaded hole is on the external side of the cylinder head.
Detach the spring (9) and remove the tool no. 88713.2783.
Proceed in the same way for the exhaust side.
Install the valve (17) and valves (16), first lubricating them with engine oil.
Provisionally install the camshaft (C).
Using two screwdrivers, hold the closing rocker (18) in the “valve open” position.
Fit the closing shim (8) on the valve stem (17) with the larger diameter side facing the rocker arm.
Position the two half rings (7) on the valve stem.
Remove the screwdriver and position the closing rocker arm (18) in the rest position.
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 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 specified clearance has been obtained, remove the camshaft (C), lubricate it with graphite oil and reinstall it in the cylinder head.
Insert the rocker arm shaft (4) with the threaded hole on the external side of the cylinder head: the seal (5) should be renewed on installation; lubricate it before fitting.
Locate the opening rocker arm (3) and the two shims (2) on the shaft (4).
Refit the camshaft end cap (Sect. N 4.3, Refitting the camshaft end caps).
Refit the camshaft timing pulleys (Sect. N 4.2, Refitting the timing belt driveshaft pulleys).
Locate the valve opening shim (6) on the valve stem.
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 (Sect. N 4.1, Checking and adjusting valve clearances.
Fit the side clip (1) on the shaft (4) of the opening rocker arm (3) between the two spacers (2).

Operation | Section reference
Refit the valve covers | N 4.3, Refitting the valve covers

Refitting the cylinder heads
Warning
In order to prevent oil leaks developing between the cylinder barrel and the crankcase, every time the cylinder head is removed, it is essential to remove also the cylinder barrel/piston in order to be able to clean the crankcase and cylinder barrel, to renew, if necessary, damaged gaskets and O-rings and to apply new liquid gasket (Sect. N 5, Refitting the cylinder/piston assembly).
Before refitting the cylinder head assemblies, fit new head gaskets (C) and check that the locating dowels (A) and bushes (B) are installed (Sect. N 5, Cylinder/piston assemblies).
Fit the cylinder head onto the studs and lower it down onto the cylinder barrel.
Fit the special washers (12) over the stud bolts with the square edged face towards the cylinder head and the flat face towards the inside.
Grease the threads and undersides of the nuts (19) and the threads of the studs with the recommended grease.
Using tool no. 88713.2676 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).
Important
Incorrect tightening could cause abnormal elongation of the studs and serious damage to the engine.

Operation | Section reference
Refit the timing belt covers and the timing belts | N 4.2, Refitting the timing belt tensioner pulleys
Refit the engine to the frame | N 1, Refitting the engine

N