Non-positive system used until February 1964. This uses a hose from the rocker cover to the front air-cleaner (outside the filter) and a non-ventilated oil filler cap. The other end of the system (not visible) is a hose on a port on the timing cover and just hanging down with an open end. (Photo: Clausager, Original MGB)
In February 1964 a positive ventilation system was implemented. Until October 1968 it consisted of a PCV valve mounted on the inlet manifold, plumbed to a port on the front tappet chest cover. The oil filler cap is now ventilated with a restriction and a filter. (Photo: Clausager, Original MGB)
In October 1968 the PCV valve was replaced by carb ventilation, with ports on both carbs connected together and taken down to the front tappet chest cover. The oil filler cap is ventilated as before. This system was used on UK cars until the end of production.
North American spec from October 1969 with the charcoal cannister. Originally with twin SUs connected to the front tappet chest cover as before, but with a non-vented oil-filler cap. This version shows the later single Zenith/Stromberg carb and anti-runon valve. (Photo: Clausager, Original MGB)
V8 with individual hoses and oil/flame traps from carbs to rocker covers.
Rear of the V8 air-cleaner box showing the breather intake filter with mounting clip and hoses.
