Cub Cadet MTD P71 Series - Manual (Page 33)

B ASIC T ROUBLESHOOTING
27
PCV testing
The PCV (Positive Crankcase Ventilation) valve is
located in the engine block and allows the crankcase pres-
sure to escape.
Leakage and blockage are the two failure modes for a
PCV system. Either mode will cause crankcase pressure
to build-up, though the effects of a blocked PCV are gener-
ally more dramatic. Increased case pressure will result in
oil entering the combustion chamber.
NOTE: The PCV chamber is vented to the carburetor
throat through a molded rubber hose. See Figure
2.4.
To measure the crankcase pressure:
1. Remove the dipstick.
2. Attach a manometer to the dipstick tube.
3. Start the engine.
4. Read the measurement on the manometer. See
Figure 2.5.
NOTE: A typical reading, under no load, is around -10”
(-25.4cm) of water.
NOTE: Experimentation by MTD’s Training and Education
Department has revealed the following character-
istics of MTD engines:
• A leaky PCV system will not build-up substantial
case pressure.
• A leaky PCV system will allow the engine to ingest
contaminants through the system, accelerating
engine wear.
• A blocked PCV system will allow crankcase pres-
sure to build very rapidly. Noticeable oil fumes will
be evident in the exhaust within several minutes of
normal operation.
Figure 2.4
Breather hose
Figure 2.5