Compression Test - TM-10-3930-627-120052

TM 10-3930-627-12

(6) Following firing order, turn crankshaft

seal the rings and take another reading. If compression

one-half revolution and adjust valves for No. 3 cylinder.

is appreciably increased in the cylinder so treated, piston

Turn crankshaft one-half revolution and adjust valves for

or rings require replacement.

If no change in

No. 4 cylinder. Turn crankshaft one-half revolution and

compression occurs, check the valve mechanism. A

adjust valves for No. 2 cylinder.

low reading on two adjacent cylinders indicates the

possibility of a leak from one cylinder to the other at the

cylinder head gasket.

g. Install spark plugs and coil wire.

4-19. Crankcase Fluid Filter

a. Removal of Element.

(1) Turn spin-on filter element (2, fig. 4-4)

counterclockwise.

(2) Remove gasket and element from base

(8).

Figure 4-3. Adjusting valve clearance.

d. Installation of Cover.

(1) Clean the cover with SD.

(2) Reverse procedures in a above to

install cover using a new gasket.

4-18. Compression Test

A compression test is made to determine the need of

internal repairs before tune-up procedures are

undertaken. This test will indicate the condition of the

piston rings and valves. Compression pressure depends

1. Bracket

upon altitude, cranking speed, engine temperature, oil

2. Filter cartridge

viscosity, compression ratio, and condition of engine. An

3. Jam nut

engine without fairly even compression cannot be tuned

4. Elbow

properly. Make the test in the following manner:

5. Tee

a. Start engine and run until normal operation

6. Pressure sender

temperature is reached. Stop engine.

7. Adapter

b. Remove all spark plugs after cleaning dirt or

8. Base

other foreign matter out of plug wells.

Figure 4-4. Engine oil filter arrangement.

c. Remove and ground coil secondary wire from

b. Installation of Element. Using new filter

distributor cap to prevent accidental shocks while

element, reverse removal procedures.

cranking engine.

c. Removal of Filter.

d. Insert a compression gage in number one

(1) Disconnect hoses at filter.

spark plug hole.

(2) Loosen nut (3). Remove connector

e. With both throttle and choke fully open,

fittings 14 and 7.).

crank engine with the starting motor and record the

(3) Remove screws, lockwashers, and nuts

highest reading obtained. Do not crank engine more

securing filter bracket (1) to frame.

than is necessary (six revolutions will be sufficient).

d. Cleaning and Inspection. Clean the filter

Record readings on other cylinders in the same manner.

base

f. Compare pressure of the cylinders. Cylinder

pressure should not vary more than 15 psi. Should one

or more cylinders show low compression, pour enough

light engine oil on top of piston with low compression to

4-7