The exhaust manifold collects exhaust gases from the cylinder head ports and directs them into the front pipe of the exhaust system. The manifold type determines the front pipe connection method and must be matched to the exhaust system fitted, fitting a bell-type front pipe to a flange-type manifold (or vice versa) is not possible without modification.
1275cc Exhaust Manifolds
Two cast iron exhaust manifold types were used on the 1275cc. The bell-type manifold has a bell-shaped outlet that receives the front pipe, with a clamp securing the joint, used in conjunction with the Type 1 and Type 2 exhaust systems. The flange-type manifold has a flat flange with three studs, providing a more positive connection via a bolted joint with brass nuts, used with the Type 3 system. The manifold-to-head connection is common to both types, using six studs with brass nuts.
A single combined inlet and exhaust manifold gasket seals both manifolds to the cylinder head, since the inlet and exhaust manifolds bolt together at the head face on the A-Series engine.
Manifold Stud Removal
When removing or refitting manifold studs, care must be taken not to damage the threads in the cast iron cylinder head. Studs should be wound in by hand or with a stud extractor tool, never forced.
If a stud seizes and breaks during removal, the head must be removed for extraction and thread repair, typically requiring a thread insert if the original threads cannot be salvaged. Brass nuts are essential on all manifold studs as they resist heat-cycling corrosion and make future removal far easier than steel nuts, which seize and frequently shear.
1500 Exhaust Manifold
The 1500 exhaust manifold is specific to the Triumph engine and is not interchangeable with any 1275cc manifold. It connects to the head via studs and clamps with an inner and outer clamping arrangement, using brass nuts and special long nuts at specific positions. The manifold-to-downpipe connection uses a gasket rather than the bell or flange joint of the 1275cc, sealing against the cast flange of the 1500 manifold.
Performance Manifolds
Tubular performance exhaust manifolds are available in both stainless steel and mild steel for the 1098cc, 1275cc, and 1500cc. A tubular manifold replaces the restrictive cast iron original with individual primary pipes that merge into a collector, improving exhaust gas flow and providing a measurable increase in power, particularly noticeable in the upper rev range where the cast manifold's restriction is most apparent.
When fitting a tubular manifold, the carburettor needles may need to be changed to a richer profile to compensate for the improved exhaust scavenging effect. Exhaust wrap and fixing sets are available for those wishing to insulate the manifold to reduce underbonnet temperatures and minimise heat soak into the carburettor area.