Two cast iron exhaust manifold types were fitted to the 1275cc Midget, and the type fitted determines which exhaust system front pipe connection method is used. The bell-type manifold (part number 12G420) has a bell-shaped outlet that receives the flared end of the front pipe, with an external clamp compressing the flare against the bell to create a gas-tight seal. This manifold was used with the Type 1 and Type 2 exhaust systems from 1967 to 1972.
Exhaust System
The flanged manifold (12G1581) has a flat flange with three stud holes, onto which the front pipe bolts using an olive (cone-shaped sealing ring) compressed between the flange face and the pipe. This design was introduced for the Type 3 system from 1973 and provides a more positive, reliable seal than the bell-and-flare arrangement. The flanged manifold is generally regarded as the superior design, and some owners retrofit it to earlier cars when replacing the exhaust system.
System Specification
Both manifolds connect to the cylinder head via six studs with brass nuts. The brass nuts are essential, they resist the corrosive effects of repeated heat cycling far better than steel nuts, and they will not seize onto the studs in the way that steel does. Even with brass nuts, applying anti-seize compound to the stud threads during fitment is strongly recommended. A manifold stud that seizes and breaks during future removal is one of the most time-consuming and frustrating workshop problems on any classic car, the broken stub must be drilled out and the thread repaired, often with the cylinder head still on the engine.