Overhauling the cylinder head components
Cylinder heads
Remove any carbon deposits from the combustion chamber and its ducts.
Remove any scale from the coolant ducts.
Check for cracking and inspect the sealing surfaces for scoring, steps or other damage.
Check that the cylinder mating surfaces of the cylinder head are free of carbon deposits and scale. If this is not the case, spread diamond lapping paste (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 surface is obtained.
Valve seats
Visually inspect the valve seats: there must be no pitting or cracks.
Minor damage can be repaired by grinding with special 45° and 60° single-blade grinders. Grind the valves and check the seal.
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.
Proceed as follows.
Remove the worn seats, grinding carefully to avoid any damage to cylinder head housings.
Check the diameter of head housings and choose the oversized valve seat that will give an interference fit of 0.04 to 0.10 mm.
Heat the cylinder head gradually and evenly up to 150 °C and chill the new valve seats in dry ice.
Drive the seats perfectly square into the head housings using the appropriate valve guide seat installers 88713.2846 and 88713.2847.
Allow the cylinder head to cool down and grind the seats to the following dimensions:
CA = Ø 41.6 ± 0.025 mm.
CS = Ø 33.6 ± 0.025 mm.
S = 1.2 mm.
D = 0.2 to 0.4 mm.
Important
Do not use any lapping compound after final grinding.
It is advisable to lap the radius between the intake valve seats and the intake ducts (F = before; G = after).
Valve guides
Check the internal surface of the valve guides: there should be no signs of deformation or cracking.
Thoroughly check the dimensions of the valve guide.
Measure the inside diameter with a suitable gauge.
Measure the diameter at different positions of the valve guide.
The clearance upon fitting must be: maximum detected value - minimum detected value = 0.03÷0.045 mm.
The maximum permissible wear limit is 0.08 mm.
Change the valve guides when the ovality exceeds permissible limit or the valve stem clearance is outside the tolerance range.
When you change the valve guide, you must also change the valve.
Valve guides as spare parts are available with outside diameter oversized by 0.03, 0.06 and 0.09 mm.
Change the valve guides as follows:
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heat up the cylinder head gradually and evenly up to 150 °C;
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remove the original valve guides using tool no. 88713.2842;
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allow the cylinder head to cool down and check the condition of the seats;
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choose suitable valve guides to obtain an interference fit in the cylinder head of 0.022 to 0.051 mm;
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heat up the cylinder head again and chill the new valve guides in dry ice;
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lubricate the seats in the cylinder head and install the valve guides using the appropriate service tools and with reference to the dimensions given in the figure;
A= 22.4±0.15 mm.
B= 28.45±0.15 mm
Hone the mating surface with a reamer.
Checking the valve
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 at various points along the section that runs in the valve guide.
Check the valve stem for buckling. Place it on a "V" reference and measure deformation with a dial gauge.
Service limit: 0.053 mm.
Check the valve stem for buckling. Place the valve on a "V" reference block, set a dial gauge perpendicular to head and measure concentricity of valve face at 45°.
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nominal concentricity: 0.01 mm;
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service limit: 0.03 mm.
Use Prussian blue or a mixture of minium and oil to check that the contact surface (W) between valve and seat is 1.4 to 1.6 mm (1.05 to 1.35 mm when new).
Grind the seat if the dimension measured is greater than the above limit.
Checking the valve seal
After grinding the seats it is important to check the seal between valve face and seat: if the seat contact area (S) on the valve is wider than the 45° band (W) this could lead to poor sealing.
Checking the rocker arms
Check for signs of wear, grooves or chrome flaking off.
Check the condition of rocker arm bore and shaft.
Clearance upon fitting: 0.025÷0.049 mm
Wear limit: 0.08 mm.
Opening and closing shims - Springs
Check the condition of the contact surfaces of the valve closing (7) and opening (4) shims: there must be no signs of wear.
Check the conditions of the return springs (15) and (16) of the closing rocker arms: no cracks, deformations or failure must be present.