Chapter 2: Basic Troubleshooting
20
3. An engine that fails to purge extra case pressure
in a controlled manner will build case pressure.
The pressure will find it’s own way out of the
engine in undesirable ways.
• Oil will be forced by the rings and valve guides,
being burnt in the combustion chamber.
• The cause of this oil burning can be mistaken for
a worn-out engine, if proper diagnosis (compres-
sion, leak-down, and case pressure) is not per-
formed.
4. Experimentation by MTD’s Training and Educa-
tion Department has revealed the following char-
acteristics 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, accel-
erating engine wear.
• A blocked PCV system will allow crankcase
pressure to build very rapidly. Noticeable oil
fumes will be evident in the exhaust within sev-
eral minutes of normal operation.
5. The PCV chamber is accessible by removing the
flywheel, as described in the IGNITION SYS-
TEM chapter of this manual. See Figure 2.6.
6. Remove the two screws that hold the PCV
chamber cover to the engine block using a
10mm wrench.
7. The cover and gasket can be separated from the
chamber. See Figure 2.7.
NOTE: The dimple in the cover helps locate the
fiber disc over the port that leads into the crank-
case.
NOTE: the baffle in the cover helps separate the
oil from the air in the chamber. It is desirable to
allow the air out, but important to keep as much
oil as possible in the engine.
8. The disc acts as a check valve: pressure pulses
force it off of the port, but it falls back over the
port when the pressure drops.
9. The folded wire mesh in the chamber also helps
separate the oil from the air. See Figure 2.8.
Figure 2.6
PCV tube
PCV
chamber
cover
Dimple
Figure 2.7
Cover
Gasket
Baffle
Disc
Figure 2.8
Disc
Port to
Folded wire mesh
crankcase
PCV hose
Port to
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