CRANKCASE BREATHER SYSTEM Most Mini models are fitted with a closed crankcase ventilation system which should be inspected and serviced periodically to ensure correct functioning of the system, as otherwise a pressure build-up in the crankcase can occur, causing subsequent oil leaks in the engine with an increase in oil consumption.
The system comprises an inlet filter in the oil filler cap on the rocker cover, an oil separator and a vent tube to the inlet manifold or air cleaner. On some early models a spring loaded regulator valve is also incorporated in the system .

Fresh air enters the system through the filter in the filler cap, then passes down the push rod bores to the crankcase. The crankcase fumes are exhausted through a breather outlet pipe on the engine side cover at the front of the engine, and the oil droplets and mist are trapped by the oil separator before the fumes pass into the inlet manifold, via the regulator valve where fitted.
Intake Filter The air intake filter is incorporated in the oil filler cap, and the complete cap assembly should be renewed at least every 12,000 miles.
At the same time, the hoses in the system should be checked for blockages or leaks.
Regulator Valve The operation of the system control valve can be tested by removing the oil filler cap from the rocker cover with the engine at normal operating temperature and running at idle speed. If the valve is functioning correctly the engine speed will increase by approximately 200 rev/n-dn. as the cap is removed. The change in speed will be audibly noticeable. If no change occurs, the valve must be serviced as described below.
Release the spring clip and remove the components of the valve from the housing .
Clean all metal parts with petrol. If deposits are difficult to remove, immerse the parts in boiling water first. Clean the diaphragm. with detergent o r methylated spirits. Examine the components carefully and renew any which show signs of wear or damage. Ensure that the system connecting hoses are clear before reassembling the valve. Reassemble the components as shown in the illustration, making sure that the spigot on the metering valve engages in the cruciform guides and the diaphragm is seated correctly.
NOTE: The early type regulator valve assembly without the cruciform guides must be renewed as an assembly.