The 1500cc cylinder head is an entirely different casting from the 1275cc, with its own unique valve sizes, port layout, combustion chamber shape, and stud pattern. It uses ten head studs rather than the nine on the 1275cc, and the head gasket is specific to the Triumph engine, a 1275cc gasket will not fit.
Rocker Gear Arrangement
The rocker gear arrangement is fundamentally different from the A-Series. The 1500 uses individually numbered rocker arms, odd-numbered arms (1, 3, 5, 7) operate the valves on one side and even-numbered arms (2, 4, 6, 8) on the other, numbered from the water pump end. The rocker shaft is supported by four pillars in three different specifications: the number 1 pillar, the number 2 and 3 pillars (which share a specification), and the number 4 pillar. These are not interchangeable and must be correctly identified during reassembly, incorrect pillar positioning disrupts the oil feed to the rocker assembly.
Rocker Cover Sealing
The rocker cover sealing arrangement changed during 1500 production. Early engines (up to approximately 1977) used a cork gasket rocker cover held by conventional studs.
Later engines adopted an O-ring sealed cover with different mounting studs and nuts. The two cover types and their fixings are not interchangeable.
When fitting a chrome or alloy rocker cover to the 1500’s sealed breather system, a blanking screw is required to seal the hole in the oil filler cap that would otherwise vent to atmosphere, this is a commonly overlooked detail that causes oil mist in the engine bay if left unaddressed.