8 - Cylinder
22 - Duct for oil out of
cylinder head
36 - Cylinder fastening
nut
9 - Piston
23 - Gasket
37 - Carburetor
10 - Cylinder head
24 - Oil drain tube of
cylinder
38 - Spark plug tip
11 - Valve
25 - Compression rings
39 - H.V. wire
12 - Valve spring
26 - Piston pin
40 - Filler plug with
dipstick
13 - Adjusting bolt
27 - Oil rings
41 - Oil pump drive
gear
14 - Rockshaft
bracket
28 - Connecting rod
42 - Oil pump drive
plug
43 - Oil pump drive
pinion
As the pistons move up, the vent duct is overlapped, the
crankcase interior is cut off from the atmosphere and vacuum is
built up.
If the piston rings are in good condition, the breather maintains
permanent vacuum in the crankcase, thus excluding any
possibility of oil expelling though the seals. The crankcase
ventilation system is routed to the air cleaner. When running the
motorcycle in winter an ice plug may be formed in the tube
connecting the breather with the air cleaner leading to oil leakage
through sealing glands. Therefore, this tube should be inspected
frequently when running in very cold conditions.