Cylinder head flatness

Service Bulletin - October 1978............. number 1978/4


Cylinder head flatness

Would dealers please note that particular attention must be given to the ‘flatness’ of the cylinder head face and the stand proud dimension of liners in the cylinder block when replacing cylinder head gaskets or rebuilding engines after major overhaul.

It is important that before replacing a cylinder head all traces of old gasket material are cleaned from both the cylinder head and cylinder block mating faces. However, equally important is the flatness of the cylinder head gasket face. To obtain a suitable ‘flatness’ by removing any high spots or gasket material the following procedure should be carried out.

Spread a sheet of 80 grit paper a minimum size of 457mm (18”) long and 203mm (8”) wide over a surface table (or if a surface table is not available a sheet of 6mm (0.25”) plate glass and fasten down. Rub the cylinder head backwards and forwards ensuring the cylinder head is held parallel to the surface table over the 80 grit paper to clean the joint face, finally moving in a circular motion to remove any high spots.

When replacing the cylinder head, carefully position the head squarely on the cylinder block and secure withe twelve nuts, plain washers and lockwashers. Replace the three nuts on the spark plug side of the cylinder head. Check that all cylinder head nuts are tightened in the order indicated in figure 1 to a torque of 3.46 Kg.m (25 lb.ft) The three remaining nuts on the spark plug side should be tightened to a torque of 2.07 Kg.m (15 lb.ft)

When replacing cylinder liners smear ‘ICI Silkoset 152’ sealing compound, thinly around the seating face of the liner and its location in the cylinder block, making a thin but complete 3600 seal (Figure 2). Using tool number 90764 as shown in Figure 3. insert the liners into the block and ensure they stand proud 0.050 - 0.152mm (0.002 - 0.006 in.) from the cylinder block face. Check that there is 0.381mm (0.015 in.) clearance between liners.

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