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.