ENGINE STARTING SYSTEMS
In this chapter, we will discuss the operating principles of starting systems used with
internal-combustion engines. As an Engineman, you will be concerned with four types
of starting systems: (1) electric, (2) hydraulic, (3) air motor, and (4) compressed air
admission. Electric starting systems are used with gasoline engines and diesel engines
used in small craft (boats). The hydraulic starting system is used where nonmagnetic
or lightweight characteristics are required. The air motor system is used wherever
practicable because it contains sturdier components and requires less maintenance. Air
motors are used to start Alco, Detroit Diesel, and Caterpillar engines. The com-
pressed air admission system is used on many larger engines, such as those
manufactured by General Motors, Fairbanks-Morse, and Colt-Pielstick. For a diesel
engine to start, it must turn over fast enough to obtain sufficient heat to ignite the fuel-
air mixture. If the engine turns over too slowly, the unavoidable small leaks past the
piston rings and past the intake and exhaust valves (4-stroke cycle engines) will allow
a substantial amount of the air to escape during the compression stroke. In addition to
a loss of pressure, the heat loss from the compressed air to the cylinder walls will be
greater at low speed because of the longer exposure.
The escape of air and loss of heat result in a lower temperature at the end of the
compression stroke. Therefore, there is a minimum speed at which the diesel must
turn over before ignition will occur and the diesel will begin firing. The starting speed
depends on the size and type of the engine, and the temperature of the air entering the
cylinders.
After reading the information in this chapter, you should be able to describe the four
types of starting systems and their methods of operation. You should also be aware of
the devices that can be used to help a diesel engine start in cold weather. These
devices are commonly referred to as starting aids.
ELECTRIC STARTING SYSTEMS In this section, we will discuss basic electrical systems that apply to small marine craft (boats). You, as an Engineman, may be required to perform basic maintenance on an electrical starting system for a small boat engine when an electrician is not available. Electric starting systems use direct current because electrical energy in this form can be stored in batteries and can be drawn upon when needed. The battery’s electrical energy is restored when the battery is charged with an engine-driven generator or alternator. The main components of the electric starting system are a storage battery, starting motor, and associated control and protective devices. Figure 10-1 shows a typical cranking system.
BATTERIES
The lead acid storage battery provides the power source for starting small boat
engines and other types of small and medium size engines. Most starting motors for
the engines in small craft are rated for 24 to 28 volts. To supply the required current
for starting, four individual 6-volt batteries are connected in series.
For maximum efficiency and long life of the storage battery, periodic inspections are
essential. Batteries that serve to start boat engines are subjected to moderately heavy
use and may require frequent charging in addition to the charging provided by the
engine generator or alternator.
MONITORING THE CHARGING SYSTEM
As an operator, you should be aware of the condition of the charging system of the
engine. You can use the ammeter to monitor the charging system. An ammeter is a
device that is wired into the electrical circuit to show the current flow to and from the
battery and is mounted on the gauge board (panel) along with the other monitoring
gauges. After the engine is started, the ammeter should register a high charge rate at
the rated engine speed. This is the rate of charge received by the battery to replenish
the current the battery has used to start the engine. As the engine continues to operate,
the ammeter should show a decline in the charge rate to the battery. The ammeter will
not show a zero charge rate since the regulator voltage is set higher than the battery
voltage. The small current registered prevents rapid brush wear in the battery-charging
generator. If lights or other electrical equipment are connected into the circuit, the
ammeter should show discharge when these items are operating and the engine speed
is reduced. Information on the electrical devices we have discussed is presented in
detail in Navy Electricity and Electronics Training Series (NEETS), modules 1
through 5 (latest editions).
STARTING MOTORS AND DRIVES
The starting motor for a diesel or a gasoline engine operates on the same principle as a
direct current electric motor. The motor is designed to turn extremely heavy loads but
tends to overheat quickly because it draws a high current (300 to 665 amperes). To
avoid overheating, NEVER allow the motor to run for more than the specified amount
of time. Then allow it to cool for 2 or 3 minutes before using it again. Refer to the NA
VSEA technical manual for your engine for the recommended cranking and cooling
periods.
The starting motor is located near the flywheel. (See fig. 10-1) The drive gear on the
starter is arranged so that it can mesh with the teeth on the flywheel (or the ring gear)
when the starting switch is closed. The drive mechanism has two functions: (1) to
transmit the turning force to the engine when the starting motor runs and to disconnect
the starting motor from the engine immediately after the engine has started and (2) to
provide a gear reduction ratio between the starting motor and the engine. (The gear
ratio between the driven pinion and the flywheel is usually about 15 to 1. This means
that the starting motor rotates 15 times as fast as the engine, or at 1500 rpm to turn the
engine at a speed of 100 rpm.)
The drive mechanism must disengage the pinion from the flywheel immediately after
the engine starts. After the engine starts, the engine speed may increase rapidly to
approximately 1500 rpm. If the drive pinion were to remain meshed with the flywheel
and locked with the shaft of the starting motor, at a normal engine speed (1500 rpm),
the shaft would spin at a rapid rate of speed (between 22,500 and 30,000 rpm). At
such a rate of speed, the starting motor would be badly damaged.
Bendix Drive Mechanisms
Figure 10-2 illustrates a starting motor equipped with a Bendix drive friction-clutch
mechanism. The drive mechanism moves the drive pinion so that it meshes with the
ring gear on the flywheel.
The pinion of the Bendix drive is mounted on a spiral-threaded sleeve so that when
the shaft of the motor turns, the threaded sleeve rotates within the pinion, moving the
pinion outward, causing it to mesh with the flywheel ring gear and crank the engine.
A friction clutch absorbs the sudden shock when the gear meshes with the flywheel.
As soon as the engine runs under its own power, the flywheel drives the Bendix gear
at a higher speed than that at which the shaft of the starting motor is rotating. This
action causes the drive pinion to rotate in the opposite direction on the shaft spiral and
automatically disengages the drive pinion from the flywheel as soon as the engine
starts.
Special switches are needed to carry the heavy current drawn by starting motors.
Starting motors that have a Bendix drive use a heavy-duty solenoid switch (relay
switch) to open and close the motor-to-battery circuit and a hand-operated starting
switch to operate the solenoid switch. The starting switch is on the instrument panel
and may be a push-button or a lever type. The solenoid switch (fig. 10-3) is mounted
on and grounded to the starting motor housing so that the wires that must carry the
heavy current required by the motor may be as short as possible to prevent voltage
loss and overheating resulting from current draw. When the solenoid is energized by
the starting switch, the plunger is drawn into the core and completes the circuit
between the battery and the starting motor.
Operating precautions on the Bendix drive must be strictly followed. There are times
when the engine may start, throw the drive pinion out of mesh, and then stop. When
the engine is coming to rest, it may often rock back part of a revolution. If at that
moment the pinion is engaged, the drive mechanism may be seriously damaged.
There-fore, you must wait several seconds to be sure that the engine is completely
stopped before you use the starting switch again. Sometimes the pinion will fail to
engage immediately after the starting motor has been
Figure 10-3.-A typical solenoid switch assembly.
energized. When this happens, you will not hear the engine turning over and the
starting motor will develop a high-pitched whine. You should immediately de-
energize the starting motor to prevent overspeeding. An electric starting motor
operating under no-load conditions can quickly overspeed and can be seriously
damaged.
If the pinion is to engage and disengage freely, the sleeve and the pinion threads
should be free from grease and dirt. The Bendix drive should be lubricated according
to instructions in the NAVSEA technical manual.
Figure 10-2.-Cross section of a starting motor with a Bendix drive.
Dyer Drive Mechanism
Figure 10-4 shows a starting motor assembly with a Dyer drive mechanism. Figure
10-5 shows an exploded view of the drive assembly. Refer to figures 10-4 and 10-5 as
you read the discussion of the Dyer starter mechanism.
The starting motor shown in figure 10-4, equipped with a Dyer shift drive, is operated
through a solenoid starting shift and switch. The solenoid assembly is mounted on the
starting motor and is connected to the battery and motor. Remote control starting is
accomplished by a starter switch on the instrument panel which, upon being closed,
energizes the starter solenoid. A heavy-duty plunger inside the solenoid is connected
by linkage to the pinion shift lever that operates the Dyer drive. When the starter
switch is closed, the battery energizes the coil of the solenoid switch which pulls the
pinion gear into mesh with the ring gear on the flywheel. Continua-tion of the plunger
movement closes the solenoid switch contacts, thereby removing the coil from the
circuit and permitting the cranking motor to crank the engine.
The Dyer drive consists of a splined section on the armature shaft, a shift sleeve,
pinion, gear pinion guide, pinion stop, thrust washers, and springs. (See fig. 10-5.)
The thrust washers furnish a thrust bearing for the shift sleeve when it is in the
returned position. The springs aid in the lock operation and in the engagement action.
Figure 10-5.-Dyer shift drive mechanism.
The entire drive is contained in the starting motor drive housing. The movement of the
pinion is controlled by a shift lever which is connected directly to the shift sleeve.
The Dyer drive provides a positive engagement of the cranking motor pinion gear
with the engine
Figure 10-4.-A starting motor with a Dyer shift drive.
flywheel before the cranking motor switch contacts are closed or the armature is
rotated. This design prevents the pinion gear teeth from clashing with the flywheel
ring gear. It also prevents the possibility of broken or burred teeth on either the ring
gear or the drive pinion gear. The pinion gear is thrown out of mesh with the flywheel
by the reversal of torque as the engine starts.
The operation of the Dyer drive mechanism is similar to that of the Bendix drive. The
four stages of operation are shown in figure 10-6. In view A, the mechanism is in the
disengaged position. In view B, the starting switch has been energized and the
solenoid is pulling its plunger in and is beginning to move the pinion gear toward the
ring gear. In view C, the pinion gear has fully meshed with the ring gear, but the
motor shaft has not begun to rotate. In view D, the motor shaft is rotating and the shift
sleeve has returned to its original position. The drive pinion is moving the flywheel
ring gear which cranks the engine.
Sprag Overrunning Clutch Drive
Another type of drive mechanism used by the Navy is the Sprag overrunning clutch.
This type
Figure 10-6.-Dyer drive operation.
of drive is similar to the Dyer drive in that the pinion is engaged by the action of a
lever attached to the solenoid plunger. Once engaged, the pinion will stay in mesh
with the ring gear on the flywheel until the engine starts or the solenoid switch
disengages. To protect the starter armature from excessive speed when the engine
starts, the clutch "overruns" or turns faster than the armature, which permits the starter
pinion to disengage itself from the ring gear.
The solenoid plunger and shift lever, unlike the Dyer drive, are completely enclosed
in a housing to protect them from water, dirt, and other foreign matter. An oil seal,
installed between the shaft and lever housing, and a linkage seal, installed around the
solenoid plunger, prevent transmission oil from entering the starter frame or solenoid
case. The nose housing of the drive mechanism can be rotated so that a number
The General Motors hydro starter system, as illustrated in figure 10-7, is a complete
hydraulic system used for the cranking of internal-combustion engines. The system is
automatically recharged by the engine-driven hydraulic pump after each engine start.
The starting potential of this system does not deteriorate during long periods of
inactivity. Continuous exposure to hot or cold climates also of solenoid positions can
be obtained with respect to the mounting flange.
HYDRAULIC STARTING SYSTEMS
Hydraulic starting systems are used on various small diesel engines. In our discussion,
we will use the General Motors hydrostarter system as an example.
Figure 10-7.-Hydraulic starting system.
has no detrimental effect upon the hydrostarter system. Engine starting torque for a
given pressure will remain fairly constant regardless of the ambient temperature.
The hydrostarter system consists of a reservoir, an engine-driven charging pump, a
manually operated pump, a piston-type accumulator (with a fluid side and a nitrogen
side), a hydraulic, vane-type starting motor, and connecting lines and fittings.
Hydraulic fluid oil flows by gravity (or by a slight vacuum) from the reservoir to the
inlet of either the engine-driven pump or the hand pump. Fluid discharged by either
pump is forced at high pressure into the accumulator and is stored at approximately
3250 psi under the pressure of compressed nitrogen gas. (Nitrogen is used instead of
compressed air because nitrogen will not explode if seal leakage permits oil to enter
the nitrogen side of the accumulator.) When the starter is engaged with the ring gear
on the fly-wheel of the engine, and the control valve is opened, high pressure fluid is
forced out of the accumulator by the action of the piston from the expanding nitrogen
gas. The fluid flows into the starting motor, which rapidly accelerates the engine to a
high cranking speed. When the starting lever is released, the spring action disengages
the starting pinion and closes the control valve. This action stops the flow of hydraulic
oil from the accumulator. The used fluid returns from the starter directly to the
reservoir. (See directional arrows in fig. 10-7.)
During engine operation, the engine-driven charging pump runs continuously and
auto-matically recharges the accumulator. When the required pressure is attained in
the accumulator, a valve within the pump body opens and the fluid discharged by the
pump is bypassed to the reservoir. When the system is shut down, the pressure in the
accumulator will be maintained.
The hand pump of the hydrostarter system is a double-action piston pump. It serves to
pump fluid into the accumulator for initial cranking when the accumulator has
exhausted all the fluid stored in it. The starter is protected from high speeds of the
engine by the action of an over-running clutch.
The hydraulic starting system may be used with most small engines now in service
without modification other than the clutch and pinion assembly, which must be
changed when a conversion from a left-hand to a right-hand rotation is made.
AIR STARTING SYSTEMS
In this section, we will discuss the types of starting systems that derive their power
from the pressure of compressed air. The first part of our discussion will cover the
ways in which starting air is delivered to the starting system.
SOURCES OF STARTING AIR
Starting air comes directly from the ship’s medium-pressure (MP) or high-pressure
(HP) air service line or from starting air flasks which are included in some systems for
the purpose of storing starting air. From either source, the air, on its way to the
starting system, must pass through a pressure-reducing valve, which reduces the
higher pressure to the operating pressure required to start a particular engine.
A relief valve is installed in the line between the reducing valve and the starting
system. The relief valve is normally set to open at 12 percent above the required
starting air pressure. If the air pressure leaving the reducing valve is too high, the
relief valve will protect the system by releasing air in excess of a preset value and
permit air only at safe pressure to reach the starting system of the engine. Additional
information on pressure relief valves and pressure reducing valves will be provided in
chapter 13 of this rate training manual.
In the following sections, we will discuss two common types of systems that use air as
a power source for starting diesel engines-the air starting motor system and the
compressed air admission system.
AIR STARTING MOTOR SYSTEM
Some larger engines and several small engines are cranked over by starting motors
that use compressed air. Air starting motors are usually driven by air pressures
varying from 90 to 200 psi.
Figure 10-8 shows an exploded view of an air starting motor with the major com-
ponents identified. Figure 10-9 shows the principles by which the air starting motor
functions. As you read the following dis-cussion on the flow of air through the
starting motor, refer to figure 10-9. For the relative position of the principal
components, refer to figure 10-8.
In figure 10-9, starting air enters through piping into the top of the air starter housing
(1) and flows into the top of the cylinder (2). The bore (3) of the cylinder has a larger
diameter than the rotor. The rotor (4) in-side the cylinder is a slotted rotating member
which is offset with the bore of the cylinder. The rotor carries the vanes (5) in slots,
allowing the vanes to maintain contact with the bore of the cylinder. The pressure of
the starting air against the vanes forces the rotating member to turn approximately
half-way around the core of the cylinder, where exhaust ports (6) allow the air to
escape to the atmosphere. A shaft and a reduction gear connect the rotating member to
a Bendix drive, which engages the ring gear of the flywheel to crank the engine.
Figure 10-9.-Flow of air through an air starting motor.
Figure 10-8.-Air starting motor (exploded view).
COMPRESSED AIR ADMISSION SYSTEM
Most large diesel engines are started when compressed air is admitted directly into the
engine cylinders. Compressed air at approximately 200 to 300 psi is directed into the
cylinders to force the pistons down and thereby turn the crankshaft of the engine. This
air admission process continues until the pistons are able to build up sufficient heat
from compression to cause combustion to start the engine.
Refer to figure 10-10. The engine is started by the admitting of compressed air into
the right-hand bank of cylinders. Control valves and devices that permit compressed
air to flow to the cylinders are actuated by control air that is directed through the
engine control system. The heart of the engine control system is the main air start
control valve. (A cutaway view of
Figure 10-10.-Compressed air admission starting system (Colt-Pielstick).
this valve is shown in fig. 10-11.) Except when the engine is being cranked, this
component acts as a simple stop valve. A small amount of air is routed through the air
supply port (A) to the spring side of the starting air valve. This air pressure, along
with the force of the main spring, holds the main starting air valve against its seat.
(Air pressure is the same on both sides of the piston inside the valve body; however,
the surface area inside the piston (at the bottom) is less than the bottom area outside
the piston. So the spring is required to hold the piston down against the seat. When air
pressure acting on the piston becomes unbalanced, such as when air pressure on the
inside of the piston is reduced, air pressure acting on the larger surface area on the
outside of the piston will force the piston up off the seat of the starting air valve.) As
long as the main starting air valve remains seated, starting air cannot pass through the
control valve and enter the air start manifold. However, when compressed air is
needed for the engine to start, the drain valve is forced downward, either by air that is
brought in through the control air inlet by pilot air or by the pin attached to the manual
start lever. When the drain valve is in the proper position, pressurized air above the
main spring in the start control valve escapes through the vent ports at the top of the
valve body. The resulting release of pressure allows the main starting valve to
overcome the spring force and to lift off its seat. In turn, compressed starting air is
permitted to pass through the control valve and into the air start manifold. Starting air
will continue to pass through the main air start control valve until the drain valve is
closed. When the drain valve closes, the area above the piston repressurizes and forces
the main starting valve back on its seat. This
Figure 10-11.-Main air start control valve.
reseating action shuts off starting air through the control valve.
The air start manifold runs parallel to the right bank of cylinders. Jumper lines are
connected only to the right bank of cylinders because only one bank of cylinders
needs to be attached to the air starting system. The jumper lines connect the air start
manifold to the air start check valves in the cylinder head and supply the required air
pressure to the cylinders (fig. 10-10).
The entry of starting air into the cylinders is controlled by pilot air. Pilot air leaves the
main air start control valve, passes through an air filter and an oiler, and enters the air
start distributor. The air distributor is directly driven by the right camshaft. As the
camshaft rotates, pilot air is allowed to pass through a line to the appropriate air start
check valve in the firing sequence. Pilot air opens each check valve to allow high-
pressure starting air to enter the cylinder from the jumper line, force the piston
downward, and rotate the crankshaft.
The air start check valve functions as a pilot-actuated air admission valve until the
cylinders begin to fire. As the cylinders fire, pressure created by combustion exceeds
the pressure of the starting air, this condition forces the air start check valves to close,
preventing combustion gases from entering the air start manifold.
At the same time that starting air is delivered to the cylinders, control air at 200 psi is
supplied to the forward end of the pneumatic auxiliary start/stop relay and the fuel
rack activator piston. The control air causes the piston to pull the fuel racks toward the
full-fuel position. Once the engine is started, its speed is controlled by a hydraulic
governor with a pneumatic speed mechanism attached for remote engine control. The
governor is also equipped with a dial that can be used for local control of engine speed
during maintenance, or in an emergency.
The control air that operates the main air start control valve passes through a primary
safety device, the barring gear interlock (fig. 10-10). The barring gear interlock
prevents the engine from accidentally starting or rotating and also prevents the barring
gear from being engaged when the engine is running. The safety feature is provided
by the barring lever assembly. When the barring lever assembly is in place, the
interlock will not allow control air to reach the main air start control valve, and
compressed air will not be admitted to the cylinders.
Basically, all air starting systems operate similarly and contain components that are
similar in function to those used in the two types of air starting systems we have
discussed.
COLD WEATHER STARTING AIDS
Ignition in a diesel engine is accomplished by a combination of fuel injection and
compression of intake air. Diesel engines normally require longer cranking periods
than gasoline engines. At low ambient temperatures, a diesel engine is extremely
difficult or impossible to start without adequate accessories to assist in the starting
process. As the outside temperature drops, battery efficiency is reduced and cranking
load becomes high. The increased load results from higher oil viscosity. The cold
cylinder walls also chill the incoming air, and the air cannot reach the temperature
required for combustion. The methods used for helping an engine start in cold weather
include (1) heating the air in the cylinder (glow plugs); (2) heating the intake air (grid
resistor); (3) adding a volatile, easily combustible fluid (ether) to the intake air; or (4)
heating the coolant and/or lubricating oil (heaters).
GLOW PLUGS
Deriving its power from the battery, the glow plug is a low-voltage heating element
that is inserted in the combustion chamber of each cylinder. The glow plug is used
briefly before the cold engine is cranked. In general, the time limit for the use of the
glow plug is dependent upon the ambient temperature and the design of the engine.
The operating temperature of a glow plug is between 1652° and 1832°F.
GRID RESISTORS
The grid resistor usually consists of an electrical resistance grid mounted on a frame
and supported by insulating blocks in the engine air-intake manifold. The grid is
preheated by current from the starting battery, before the engine is cranked, and is
operated during the cranking period until the engine has reached operating speed.
The basic drawback in the use of glow plugs or the grid resistor as starting aids is that
they require battery power that is also needed for cranking. The cranking power of a
battery is already reduced at low temperatures. In the following examples, note how
the cranking power of a battery is reduced as the ambient temperature drops:
PERCENTAGE OF AMBIENT CRANKING POWER OF TEMPERATURE
BATTERY
80°F 100 percent
32°F 65 percent
0°F 45 percent
ETHER PRIMERS
A widely used cold weather starting aid for engines of small craft is the ether capsule.
The ether capsule serves to inject a highly volatile fluid (ether) into the air intake
system to assist ignition of the fuel.
An ether capsule primer (fig. 10-12) consists of a discharge cell, discharge nozzle, and
pressure primer capsule, which contains a liquid ether mixture. The discharge cell and
the discharge nozzle are connected together by a suitable length of tubing. The
discharge cell is a metal enclosure containing a piercing pin and a removable cap for
insertion of the pressure primer capsule. When the lever is operated, it forces the
capsule against the piercing pin.
The discharge cell is installed at the control station in a vertical position so that the
neck of the capsule is always down toward the piercing pin. The discharge nozzle is
installed through a pipe connection at the forward end of the intake manifold.
When you are using the ether capsule primer, press the engine starter switch. As soon
as the starting motor brings the engine up to cranking speed, operate the discharger
lever to discharge the capsule. Continue cranking while the ether mixture is being
forced rapidly through the connecting tube to the intake manifold where it is sucked
into the cylinders. The capsule requires approximately 15 seconds to discharge, and
the diesel engine should start during this interval.
WARNING
Ether must not be used in connection with the grid resistor or glow plug methods.
With the high volatility of ether, additional heat could cause ignition in the intake
manifold or preignition in the combustion chamber.
HEATERS
Two other types of starting aids are the cylinder-block jacket-water heater and the
engine-oil heater. When fuel enters a cold combustion chamber and the intake air is
also cold, the fuel fails to evaporate. Instead, it collects in the cylinders, washes the
lub-rication from the cylinder walls, and dilutes the crankcase oil. These problems are
corrected when the coolant or lubricating oil is heated. These heaters function to keep
the engine components warm at all times. Moreover, they minimize engine
component wear during starting and warmup. The heaters may use steam or electricity
as a heat source for the coolant or lubricating oil.
NOTE: Starting aids are not intended to correct deficiencies, such as a weak battery or
a poorly tuned engine. They are intended for use when other conditions are normal but
the air temperature is too low for the heat of compression to ignite the fuel-air mixture
in the cylinders. For additional information on starting aids refer to Naval Ships’
Technical Manual, chapter 233.
SUMMARY
As an Engineman third class, you must know the purpose and principles of operation
of the four types of starting systems used in Navy diesel engines: (1) electric, (2)
hydraulic, (3) air motor, and (4) compressed air admission.
You should be aware of the various devices that aid the starting of an engine in cold
temperatures. Starting an engine in cold weather may require the use of starting aids
that may either (1) heat the air in the cylinder, (2) heat the intake air, (3) inject a
highly volatile fluid into the air intake, or (4) heat the lubricating oil and/or the
coolant. A commonly used starting aid is the ether capsule. The basic reason for its
use is that it will not take away battery power that is needed for cranking.
If you are uncertain about the engine starting systems discussed in this chapter, you
should reread the sections that are giving you trouble before continuing to chapter 11.
Figure 10-12.-Ether capsule primer.