TM 10-3950-206-12
and hot gases are passed through the exhaust valves to
Crank engine with starting motor until air is forced out of
the exhaust manifold.
Heat left in the engine is
No. 1 cylinder past thumb or finger plugging port.
transferred to the radiator by coolants as the primary
(3) Hold a light in a position to light timing hole
cooling system. An external oil cooler, through which the
on flywheel housing. Crank engine until dead center
crankcase oil passes provides additional cooling. The
mark on flywheel lines up with pointer in timing hole (fig.
exhaust and intake valves are operated by the camshaft
Note. Do not make a 360 revolution to align
which is geared to the crankshaft. Moving parts of
D. C. with pointer. If D. C. Mark has been passed, turn engine
engine are pressure-lubricated by an oil pump driven off
counter-clockwise or repeat step indicated in 4-50 c(2).
the camshaft.
4-51. Oil Pressure Regulator Valve
4-50. Testing
a. Removal. Remove the oil pressure regulator
a. Compression Test.
valve from the engine as indicated on figure 4-34.
(1) Test battery (para 4-27).
b. Cleaning, Inspection, and Repair.
(2) Clean around spark plug ports with
(1) Clean all parts in approved cleaning
compressed air and a cloth dampened in an approved
solvent.
cleaning solvent. Remove spark plugs.
(2) Inspect the valve for damage or evidence
(3) Hold a compression gage in front spark
of wear where valve sets in block.
plug port. Crank engine with starting motor until highest
(3) Inspect the spring for weak or broken
gage reading is reached. Record reading. Repeat this
condition. If engine is not badly worn, low engine oil
process at each remaining spark plug port.
pressure can be caused by a defective spring. Normal
(4) Compression readings above 110 psi, and
oil pressure under' load should be 20-30 psi.
within 10 psi of each other are normal. If readings are
(4) Replace defective parts.
below 100 psi or are irregular, seal the piston with a
c. Installation. Install the oil pressure regulator
teaspoon of engine oil poured through spark plug hole
valve in the engine block in reverse of the instructions on
and take new readings. If readings are below 110 psi or
if readings at different ports vary more than 10 psi,
the valves or valve seats are burned, piston rings are
worn, or there are other internal engine problems.
(5) If compression fails to read within required
range, report to proper authority.
b. Vacuum Test.
(1) Remove intake manifold pipe plug. In- stall
an adapter and connect a vacuum , gage to. the adapter.
(2, ) With engine at operating temperature and
running at idle speed adjust carburetor idle mixture
adjusting screw for highest vacuum gage reading.
(3) A vacuum reading of 18 to 22 inches of
mercury with a slight needle flutter is normal. Readings
below this range or extreme our erratic needle flutter
may indicate burned valves, improper valve or ignition
timing, improper carburetor adjustment, dirty air cleaner,
exhaust obstruction, or other engine difficulties.
(4) If vacuum reading is out of required range,
report to proper authority.
(5) Remove gage and adapter and replace
manifold plug.
c. Ignition Timing Test and Adjustment.
(1) Set contact gap (para 4-26).
(2) Remove spark plug (No.
1) nearest
Figure 4-33. Ignition timing
radiator. Place a finger or thumb over spark plug port.
4-39
