STAGE TWO SPEC. BUDGET LARGE BORE CYLINDER HEAD AEG592 Inlet valve : 35.6mm (1.401") diameter, standard ‘S’ spec. material CAM4601 Exhaust valve : 29.3mm (1.156”) diameter, latest lead free spec. material 12G1963 Guides : OE specification cast iron, bullet nosed C-AEA526 Valve springs : Nominal 180lb progressive rate dual spring. Max valve lift 0.500" ADU4905 Stem seals : Latest ‘top hat’ design, on inlets only Chamber vol. : Nominal 21cc Exhaust seats : Latest specification inserts for lead free fuel - C-AHT135 only. Not available as spares. Modified to give maximum performance gain for cost. Combustion chambers, inlet and exhaust ports extensively reworked. Stone-ground finish in ports promotes ultimate atomisation. Three angle valve seats in head. Standard Cooper ‘S’ size valves used. Combustion chamber volume used to boost standard compression ratio slightly for given application. Head modifications applied greatly increase volumetric efficiency, boosting actual working compression ratio. Compression ratio needs to be increased on lower compression engines where modified cam is used to maximise potential. Seek advice on what is needed. Before fitting to engine, ensure block and head mating surfaces are thoroughly cleaned. If fitting to a new/re-machined block, clean surface with grease-free cleaning agent (cellulose thinners highly recommended), lay gasket on block, then fit studs. This minimises possible damage to gasket during fitment. If being fitted to an engine that has already been running, remove all head studs so block surface can be thoroughly cleaned. Remove all traces of old gasket, then finish clean with cleaning agent and continue as above. Arrange pistons so that numbers 1 and 4 are at top dead centre - this minimises loading on valve gear allowing even torque down of head. Thoroughly clean head surface with cleaning agent, then lower lightly down onto block - DO NOT DROP/FORCE IT DOWN, it will damage the head gasket. ABSOLUTELY NO GASKET CEMENT OF ANY TYPE IS NECESSARY. The proper ‘A’ series head gaskets have a coating of lacquer that adheres to head and block faces when hot. Fit push rods and any relevant ancillary studs (rocker gear, thermostat housing, etc.). Back adjuster screws on rocker gear off as far as they will go, and fit to head ensuring push rod cups line up under adjuster screws ball ends. Fit head nuts (and washers if applicable), tightening finger tight, then nipping down with socket in sequence described in workshop manual. Torque down in sequence to 35lb ft first, then 50lb ft. Torque rocker gear forward studs to 25lb ft. If no by-pass hose is being used, it is essential that the outer ring of the thermostat is drilled in 4 or 6 places with an 1/8" drill to allow water circulation until thermostat opens. If no thermostat is being used, a blanking sleeve MUST be fitted. Failure to use either will result in localised overheating of chambers 3 and 4 causing excessive heat leading to pre-ignition, detonation, piston failure and cracking of the head . Water pump port must be blanked off (can use blanking plug CAM4126 and clip 3H2963).
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