TM 5-3895-346-14
CYLINDER HEADS
ENGINE OVERHAUL
To ensure efficient cooling, each fuel injector is inserted into a thin-walled tube which passes through the water
space in the cylinder head. The lower end of the injector tube is pressed into the cylinder head and flared over;
the upper end is flanged and sealed with a neoprene seal. The sealed upper end and flared lower end of the
injector tube prevent water and compression leaks.
The exhaust passages from the exhaust valves of each cylinder lead through a single port to the exhaust
manifold. The exhaust passages and the injector tubes are surrounded by engine coolant.
In addition, cooling of the above areas is further ensured by the use of water nozzles pressed into the water
inlet ports in the four-valve cylinder head. The nozzles direct the comparatively cool engine coolant at high
velocity toward the sections of the cylinder head which are subjected to the greatest heat. The coolant flow
pattern in the two-valve cylinder head is such that nozzles are not required.
The fuel inlet and outlet manifolds are cast as an integral part of the cylinder head. Tapped holes are provided
for connection of the fuel lines at various points along each manifold.
To seal compression between the cylinder head and the cylinder liner, separate laminated metal gaskets are
provided at each cylinder. Water and oil passages between the cylinder head and cylinder block are sealed
with synthetic rubber seal rings which fit into the counterbored holes in the block. A synthetic rubber seal fits
into a milled groove near the perimeter of the block. When the cylinder head is drawn down, a positive
leakproof metal-to-metal contact is assured between the head and the block.
The engine operating temperature should be maintained between 160-185 or 71-85 and the cooling
F
C
system should be inspected daily and kept full at all times. The cylinder head fire deck will overheat and crack
in a short time if the coolant does not cover the fire deck surface. When necessary, add water slowly to a hot
engine to avoid rapid cooling which can result in distortion and cracking of the cylinder head (and cylinder
block).
Abnormal operating conditions or neglect of certain maintenance items may cause cracks to develop in the
cylinder head. If this type of failure occurs, a careful inspection should be made to find the cause and avoid a
recurrence of the failure.
Unsuitable water in the cooling system may result in lime and scale formation and prevent proper cooling. The
cylinder head should be inspected around the exhaust valve water jackets. This can be done by removing an
injector tube. Where inspection discloses such deposits, use a reliable noncorrosive scale remover to remove
the deposits from the cooling system of the engine, since a similar condition will exist in the cylinder block and
other components of the engine. Refer to Coolant Specifications.
Loose or improperly seated injector tubes may result in compression leaks into the cooling system and also
result in loss of engine coolant. The tubes must be tight to be properly seated. Refer to Injector Tube.
Overtightened injector clamp bolts may also cause head cracks. Always use a torque wrench to tighten the
bolts to the specified torque.
71
