3.3
Section 3
Troubleshooting
3
Basic Engine Tests
Crankcase Vacuum Test
A partial vacuum should be present in the crankcase
when the engine is operating. Pressure in the
crankcase (normally caused by a clogged or
improperly assembled breather) can cause oil to be
forced out at oil seals, gaskets, or other available
spots.
Crankcase vacuum is best measured with either a
water manometer or a vacuum gauge (see Section 2).
Complete instructions are provided in the kits.
To test the crankcase vacuum with the manometer:
1. Insert the stopper/hose into the oil fill hole. Leave
the other tube of manometer open to atmosphere.
Make sure the shut off clamp is closed.
2. Start the engine and run at no-load high speed
(3200 to 3750 RPM).
3. Open the clamp and note the water level in the
tube.
The level in the engine side should be a minimum
of
10.2 cm (4 in.)
above the level in the open side.
If the level in the engine side is less than specified
(low/no vacuum), or the level in the engine side is
lower than the level in the open side (pressure),
check for the conditions in the table below.
4. Close the shut-off clamp
before
stopping the
engine.
To test the crankcase vacuum with the Vacuum/
Pressure Gauge Kit (see Section 2):
1. Remove the dipstick or oil fill plug/cap.
2. Install the adapter into the oil fill/dipstick tube
opening.
3. Push the barbed fitting on the gauge solidly into
the hole in the adapter.
4. Start the engine and bring it up to operating
speed (3200-3600 RPM).
5. Check the reading on the gauge. If the reading is
to the
left
of
0
on the gauge, vacuum or negative
pressure is indicated. If the reading is to the
right
of
0
on the gauge, positive pressure is
present.
Crankcase vacuum should be a minimum of 4
inches of water. If the reading is below the
specification, or if pressure is present, check the
table below for possible causes and remedies.
No Crankcase Vacuum/Pressure in Crankcase
Possible Cause
1. Crankcase breather clogged or inoperative.
2. Seals and/or gaskets leaking. Loose or
improperly torqued fasteners.
3. Piston blow by or leaky valves (confirm by
inspecting components).
4. Restricted exhaust.
1. Disassemble breather, clean parts thoroughly,
reassemble, and recheck pressure.
2. Replace all worn or damaged seals and gaskets.
Make sure all fasteners are tightened securely. Use
appropriate torque values and sequences when
necessary.
3. Recondition piston, rings, cylinder bore, valves,
and valve guides.
4. Repair/replace restricted muffler/exhaust system.
Solution
