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Cylinder Head And Gaskets

To ensure minimum distortion, wait for engine to cool before removing head bolts (1/4 - 1/2 turn at a time) in the sequence shown in Fig.1. Thoroughly clean head and block faces and check for true. Clean out all thread holes in cylinder block - use an old drill or blast with compressed air (wear goggles for this!). Check the new head gasket - is it the correct one for the engine? Check that the gasket fire ring is not smaller than the cylinder bore; gasket protrusion into the combustion chamber will result in premature failure. Some head gaskets are marked 'TOP' or 'FRONT' to ensure correct orientation when fitted. Most modern composite type gaskets have special coatings and are designed to be fitted 'dry'. A suitable sealant (e.g. Hylomar, Wellseal, etc) may be required for some applications - check fitting instructions or with supplier. And a note of caution! Enlarging gasket water-way holes will not improve cooling efficiency. The size, number and position of these holes has been finely calculated by the engine and gasket designers and any alteration may propagate localised overheating and premature engine failure.

Clean and check all cylinder head studs, nuts and bolts - replace if there is any sign of wear, stretch or damage. Most modern engines use 'stretch bolts' and these should always be renewed.

When re-fitting the cylinder head it is recommended that the bolt threads are 'lightly' oiled and installed finger tight (a light smear of anti-sieze compound under the bolt head to ease friction during the torquing process is also good practice). Many cylinder heads can be successfully secured using a method of gradual tightening (in increments of 20 lb/ft) in the sequence shown in Fig.2 (refer to manual for the final torquing figure). However, most modern engines employ stretch bolts and these must be tightened in strict accordance to the manufacturers instructions.

Re-torquing conventional cylinder head studs or bolts after an initial engine run is recommended. Always allow aluminium heads to cool completely before carrying out this process. N.B. DO NOT RE-TORQUE STRETCH BOLTS.

NOTE: When fitting a modified cylinder head don't forget to fit large bore manifold gaskets. Standard gaskets that partially mask port openings will reduce available power (Fig.3).

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Balance Bar Adjusting

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Cylinder Head And Gaskets

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