John Deere stx38 - Manual (Page 55)

4/4/97
3 - 23
ENGINE TESTS AND ADJUSTMENTS
CRANKCASE VACUUM TEST
Reason:
To measure the amount of crankcase vacuum, which
ensures the crankcase is not pressurized. A
pressurized crankcase will force oil past the seals.
Equipment:
• JTO5697 U-Tube Manometer Kit
Connections:
1. Attach manometer magnets to solid metal surface.
IMPORTANT: Connecting manometer to engine
before starting engine will cause water in the
manometer to be drawn into engine crankcase.
Do not use more than 3 feet of manometer
tubing. If a longer hose is used the manometer
readings will be inaccurate. Some engines
require a rubber hose (adapter) and hose
clamps to fit the dipstick opening while some
others require #5 plug to be shortened (cut in-
half horizontally) to obtain a tight seal.
2. Open top valves (A) and (B) one full turn.
3. Zero out the manometer by sliding the ruled scale
up or down so “0” is located where water level is
even on both sides.
Procedure:
1. Start and run engine at FAST idle to allow engine
to reach operating temperature—then move
throttle to SLOW idle.
2. Quickly remove engine dipstick and attach hose
(using adapter or plug) from manometer to dipstick
opening.
3. Tighten hose clamp or make sure plug is sealed
properly—Move throttle to FAST idle.
4. Record vacuum reading. The reading is obtained by
adding (C) and (D) water movement from “0”. In
this case reading should be 4 inches of vacuum
(2 inches + 2 inches—C + D).
5. If water movement (C) is below the “0” mark—
crankcase is pressurized causing seals to leak oil.
Crankcase should have negative pressure.
6. Repeat test at least three times for accuracy. DO
NOT shut off engine. To repeat test, remove the
manometer tube from top of manometer at valve
(A). DO NOT remove manometer tube from
engine. Be sure to reset manometer at zero—see
step 3. Reattach manometer tube to valve (A) and
record reading.
7. Remove line from manometer (valve “A”) before
stopping engine. Then remove dipstick hose,
adapter or plug connection and install dipstick.
Results:
Crankcase reading should show a minimum vacuum of
25 mm (1 in.) of water movement. V-twin engines
might show less than 25 mm (1 in.) of water movement;
this is not a problem, as long as some vacuum is
indicated, engine is operating properly. Check the
following if reading is less than minimum specification:
• Breather reed valve clearance and condition;
• Seals and gaskets for leakage, including rocker
arm cover gasket;
• Valve and valve seats for wear or damage;
• Rings, piston, and cylinder bore for wear or
damage.
A B
M55940
1
2
0
1
2
c
CAUTION
Engine components are HOT. DO NOT touch
with bare skin, especially the exhaust pipe or
muffler while making test. Wear protective eye
glasses and appropriate clothing.
1
2
0
1
2
C
D