Section XII. ENGINE TESTING

distortion that could prevent making leakproof

(2) Remove and disassemble the suction and

connections. Remove burrs with a fine stone or file.

disclarge fittings from the pump as shown in figure

Replace all damaged parts.

4-13.

c. Reassembly and Installation.

b. Cleaning and Inspection.

(1) Reassemble and install the suction and

(1) Clean all parts with an approved cleaning

discharge fittings on the pump as shown in figure 4-

solvent; dry thoroughly.

13.

(2) Inspect all parts for cracks, distortion,

wear, and other damage. Inspect all threaded parts

(2) Install the drain plug (1) and prime the

pump before starting operation of the pumping

for damaged threads. Carefully check the mating

unit.

parts of quick-disconnect fittings for burrs or

Section XII. ENGINE TESTING

organizational maintenance, report the trouble to

4-30. General

direct support maintenance.

Engine testing at organizational maintenance level

includes an operational test and a cylinder com-

4-32. Engine Compression Check

pression check. Close observation of the engine

a. A general check of engine compression can be

while operating under load, plus a compression

made by disconnecting the spark plug cable from

check which indicates the condition of the valves,

the spark plug to prevent starting, and spinning the

piston rings. and pistons, will provide fairly

flywheel with the starting rope in the direction of

comprehensive information regarding the condition

normal rotation. Considerable resistance should be

of the engine. This can be accomplished without the

noted when the piston approaches top dead center.

use of any specialized tools other than a com-

As the piston passes top dead center, the flywheel

pression gage. Perform all daily preventive

must snap over as the piston moves downward on

maintenance services before testing the engine.

the compression stroke.

b. If poor engine compression is suspected,

4-31. Operational Test

check compression with a compression gage as

a. Start the engine and operate it until it reaches

follows :

operating temperature.

(1) Remove the spark plug from the cylinder

b. Apply full load to the engine and check for a

head.

noticeable drop in engine speed when going from

(2) Use a motor or some other means to drive

no-load to full-load operation. There should be no

the engine at approximately 1000 rpm. Hold the

appreciable drop in engine speed.

throttle wide open.

c. With the engine operating at rated speed and

(3) Insert a compression gage in the spark

full load, check for visible and audible signs of

plug hole. Take several compression readings.

improper operation. Check for excessive smoke

(4) Compression readings between 110 and

from engine exhaust system or from the engine

120 psi indicate good engine compression.

breather. Black, sooty smoke from the exhaust

(5) If engine compression is low, pour a

muffler may indicate an improper carburetor

teaspoonful of engine oil into the cylinder through

adjustment. Grey smoke is usually a sign of ex-

the spark plug hole. Recheck engine compression.

cessive oil burning. Excessive smoke from the

If there is no appreciable increase in compression

breather usually results from piston ring blowby.

pressure, it indicates that the trouble is probably

d. Check the engine for knocks, tappet noise,

resulting from poor valve seating. If there is an

misfiring, backfiring, or other signs of faulty

appreciable increase in compression pressure, the

operation.

trouble is probably caused by faulty piston rings,

e. If the engine fails to operate properly, and

worn pistons, or scored cylinder walls.

correction of the trouble is not within the scope of

4-21