1 Inspect the crankcase ventilation system for blockage or damage. A blocked hose can cause a build-up of crankcase pressure, which in turn can cause oil leaks (see illustration).

35.1 Loosening the crankcase ventilation hose clip - CVH models

2 On carburettor model SOHC engines, clean the oil filler cap with paraffin and check that the vent valve is not blocked by pulling it from the oil separator and loosening the hose clip (Section 42).

3 On CVH engines, check that the oil separator and mushroom valve are not blocked, and clean if necessary (see illustration).

35.3 Oil separator (1) and mushroom valve (2) locations in air cleaner - CVH models