John-deere stx38 User Manual download pdf (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.

M55940

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.

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John-deere stx38 User Manual Page 55

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