RECIPROCATING ENGINE IGNITION AND STARTING SYSTEM

RECIPROCATING ENGINE IGNITION SYSTEMSIgnition event in four stroke cycle engine.Four stroke cycle engine consists of five events; i) Intake ii) Compression. iii) Ignition. iv) Power. v) Exhaust. Ignition takes place during compression stroke in third event.Fuel/air mixture burnt in the cylinder produce heat energy than converted to mechanical energy.

Engine Ignition systemTo produce/delivering high voltage spark to each cylinder under all operating condition.Must be able to deliver spark at specific time. (i.e. 24 BTDC)Must be high degree of reliability.Must have dual systems (as stated in FAR Part 33). i) Dual ignition system. ii) Two spark plugs for each cylinder. iii) Two separate electrical system. Advantages using two magneto systems; a) One system serve as back up if other system fail. b) Two spark plugs in one cylinder, increases combustion efficiency engine power output.

Engine Ignition SystemsSystem used either; a) Battery ignition system. b) Magneto ignition system. c) Combination of the two. BATTERY IGNITION SYSTEMUtilized a battery as source of electrical energy.This system consists of:- i) Battery. ii) Ignition switch. iii) Ignition coil. iv) Breaker point. v) Capacitor. vi) Cam. vii) Distributor. viii) H.T. lead ix) Spark plugs.

Battery Ignition System

Battery Ignition System

IGNITION SYSTEMS

Battery Ignition SystemBattery. - The source of electrical power.Ignition switch. - In the cockpit, ON circuit closed and OFF circuit open.Ignition coil. - Consists of:- Primary winding - received current from battery. Secondary winding step up voltage.Breaker point/contact point. - Convert the pure DC to pulsating DC. - Mechanical device with two electrical contact (close & open) at regular interval. - Connected in series with coil and parallel with capacitor. Capacitor / Condenser. - To prevent arcing across the contact points. - Speed up the collapsing of magnetic field.

Battery Ignition System Cam. - Consist of metallic disc with two or more raised lobes. - Opens and closes the breaker point. Distributor. - Distributes high voltage from the coil to spark plug. - Consist of rotating finger and distribution block. High tension lead. - Conductors that convey high voltage from distributor to individual spark plugs. Spark plug. - Produce high energy of spark to ignite fuel/air mixture in cylinder at specific time.

MAGNETO IGNITION SYSTEMS Magneto is a permanent magnet AC generator. It uses electromagnetic and induced current principles to develop high voltage to create spark. Designated as either; a) High tension systems. b) Low tension systems.

Magneto Ignition systemsHigh-Tension Systems. > System include a single high-tension magneto. > A wiring harness and a set of spark plug. > Utilizes a rotating magnet instead of battery. > Consist of primary and secondary winding. > The coil steps up the voltage before it goes to distributor and to spark plugs.

Magneto Ignition SystemsHigh Tension Magneto System.

High Tension System High tension magnetos are available either; a) Single magneto or b) Dual magneto. Single magneto. Consists of a permanent magnet having two, four or eight poles. Fixed to a single rotating shaft. Two single magnetos must be installed on a single engine.

High Tension Systems Dual magneto.Contain two independent ignition system that share a common rotating magnet.Dual magneto contains two of everything except the rotating magnet and cam.

High Tension SystemsProblem on early high tension magneto.Flashover is a term used to describe an occurrence inside the high-tension magneto where a spark jumps to the wrong electrode.High altitude operation increase the possibility of flashover due to lower air density.Flashover can lead to carbon tracking, which appears as a fine-like carbon trail inside the distributor.To prevent it; > Made distributor larger to increase the distance. > Use low-tension magnetos supplies low voltage to a high tension transformer at the spark plug. > Pressurized the magnetos with air above ambient to make spark difficult to jump at high altitudes. > Insulation on the ignition components.

High Tension SystemsTo prevent it; > Made distributor larger to increase the distance. > Use low-tension magnetos supplies low voltage to a high tension transformer at the spark plug. > Pressurized the magnetos with air above ambient to make spark difficult to jump at high altitudes. > Insulation on the ignition components.

Low Tension SystemsDesigned to overcome the flashover.Magneto coil has only one winding.Delivered low voltage to kept flashover at its minimum.Utilize high-tension transformers (low high voltage). Consist of primary and secondary coil.Add more components.

Low Tension System

Magneto Operating PrinciplesHigh and low-tension magneto systems operates on the same principle for generating electrical power.Low-tension not use in modern a/c.High-tension magneto consists of; a) Mechanical system. b) Magnetic circuit. c) Primary electrical circuit. d) Secondary electrical circuit.Ignition switch in the cockpit control the operation of this circuit.

a) Mechanical SystemIncludes of; - Housing. - Magneto drive shaft. - All non-electrical portion of magneto. Housing. - Made of aluminum not interfere with magnetic circuit. - Light in weight. - Mechanical strength and rigidity.Drive shaft. - Single hardened steel. - Mounted onto this drive shaft; - Rotating magnet. - Cam. - Gear to drive a distributor finger. - Supported by either ball or needle bearing.

Mechanical system conts. Magneto housing design with two types of mounting; a) Base-mounted magneto. - Bolted rigidly to a bracket on the engine accessory case. b) Flange-mounted magneto. - Used on opposed engine. - Mounting flange cast as an integral part of the housing. - Mounting holes in the flange are not circular. - L-shape lockdown tabs to clamp the flange to the engine. - Facilitates for slight magneto adjustment to the engine timing.

Mechanical system conts.Two types of cams used in high-tension magnetos:- Uncompensated and compensated cam.Uncompensated cam. - Has uniform distant between the lopes. - Equal degree of crankshaft rotation. - Number of lubes is equal to the number of poles on the rotating cam.

Mechanical System conts.Compensated cam. - Fitted to radial engine. - Separate cam lobe for each engine. - Firing event not uniform. - Spacing between each lobe is tailored to a particular cylinder. - Cam complete one revolution at every two revolution of crankshaft. - Driven by gear train.

Magnetic circuitConsist of:- - Rotating permanent magnet. - Poles shoes. - Poles shoes extension. - Coil core.Rotating magnet may be have two, four or eight magnetic poles.Arranged with alternating north and south poles that spaced evenly around the magneto drive shaft.Made of Alnico (an alloy of aluminum, iron, nickel and cobalt) and retains magnetism for an indefinite length of time.Also made of Permalloy with similar qualities.

Magnetic circuitThe rotating magnet, rotated by the engine through the gearing and rotate between the two poles.Pole shoes are joined up by coil core in order to complete the circuit.Coil core and pole shoes are laminated by the layers of high grade soft iron.The laminated layers reduces eddy current, keep magneto cooler and boosting efficiency. Allows flux lines to pass through it easily.

Magnetic circuitWhen the magnetic poles are aligned with the pole shoes, maximum number of flux lines flow through the core. ( flux flow from north to south ) - Create the strongest magnetic field. - This known as full register position.

Neutral positionWhen the magnet poles are in the neutral position (beyond full registered).The magnetic field collapsed.No lines of flux pass through the coil core.

Full register positionOnce past the neutral position, flux lines passing through the coils core increases until magnet reaches full register position again.This time the flux lines flow in the opposite direction.

Efficiency gap/E-gap angleOnce the magnet rotates beyond magnetic neutral and magnetic field of opposite polarity starts to build, at this point the greatest magnetic field exists.E-gap rotating magnet at the specific number of degrees passed/beyond the neutral position.

Primary CircuitConsist of: a) Primary Winding. b) Set of breaker point. c) Capacitor.

Primary Circuit a) Primary Winding. Magneto consists of 180 to 200 turn of 18 gauge copper wire. Wire coated with an enamel insulator. One end attach to ground lead and another end connect to the secondary winding. b) Breaker point. Mounted to the magneto housing. Held closed by leaf-type spring and open by cam. Point open at the greatest magnet stress (E-gap). Breaker point open interrupted the current flow and allow current to be induced into the secondary coil.

Primary circuit c) CapacitorInstalled parallel with the breaker point and in series with ignition switch.Reduce acing when breaker point open. - Cause delay collapse of magnetic field in the primary lead. - severe arcing could weld the point together. Also reduce electromagnetic radiation from primary lead.Feed through/filter capacitor. - Ground the radio frequency before its leave the magneto.

Secondary CircuitProduces the high voltage energy required to cause spark.Make up of: - Secondary winding. - Magneto coil. - Distributor.Amount of current induced into the secondary winding depend on: - Rate of magnetic field around the primary winding collapse. - The ratio of winding between primary and secondary. - Coil made from approximately 13,000 turns of fine wire. - Capable of producing 20,000 volts pulse. - One end attached to primary winding, path to ground and opposite end is attached to a high voltage contact at magneto body.

Secondary circuit Distributor rotor.Allow current flow from secondary winding to the distributor.A spring loaded carbon brush mounted in the centre of the distributor rotor presses against the magneto contact.Distributor consist of a conductive arm or finger that carries high voltage to the electrode for each spark plug.Driven by a gear that is mounted to the magneto drive shaft.Distributor rotor is geared to provide a high voltage path to distributor block at definite points in its rotation.Must complete one rev. for every two rev. of crankshaft.With 2:1 ratio, a magneto can fire all the spark plugs.

Distributor blockConstructed of a light-weight insulating material.Mounted in one half of the magneto housing.One side with electrodes and the other side for receptacles for spark plug lead.Electrodes and receptacles are arranged circumferentially around the distributor block.Each time the rotating magnet is in the E-gap position the distributor finger lines up with an electrode and deliver a high voltage pulse .Then routed through leads to spark plug.

Safety GapProtect the secondary winding in a magneto coil.Provide alternate path for current if there is an open in secondary circuit.This backup ground path called safety gap.Connected in series with the secondary winding by two electrode.Any excessive voltage induce into the secondary winding jumps to safety gap to ground.This to ensure voltage in the secondary winding does not rise high enough to damage the magneto coil.

Magneto speedDistributor rotor in a magneto always rotate one-half the engine crankshaft speed.Engine crankshaft must complete two rev. in order to fire each spark plug once.Speed of the distributor is set, rotating magnet shaft varies with the number of cylinders and number of poles.Eg. Number of cylinders = 6 = 3 = 1 2 x number of poles 2x2 4

- If engine turning at 2,000 rpm the magneto rotate at 3,000 rpm.

Auxiliary Ignition SystemsWhen magneto turns at slow speed, its produces relatively little voltage.As magneto speed increases the amount of current induced into primary circuit increases and produced higher voltage spark.At low magneto speed, voltage generated is insufficient to fire a spark plug.To produce enough voltage to fire the spark plug is known as coming on speed. Speed is between 100 200 rpm.To start an eng. starter cannot crank eng. fast enough for magneto to reach its coming on speed.Spark normally occurs prior TDC on the compression stroke. Normal ignition timing can cause an eng. to kick back.To prevent kick back, magneto use a second set of retard breaker points to retard the spark during eng. starting.Retard mean to delayed the spark until its reaches TDC on the compression stroke.Retard ignition, make it easy to start but does not increase the voltage. All magneto incorporate ignition booster or auxiliary ignition unit. Ignition booster includes:- the impulse coupling, induction vibration, shower of spark ignition system and booster magneto.

Impulse couplingWidely used on auxiliary ignition system.Is a small spring-loaded device.Provide a magneto with momentary high rotational speed and a retarded spark.Uses a spring loaded mechanical linkage that wound up by the magneto drive gear and released to increase rotational speed.Impulse coupling consist of: - Impulse coupling body. - Flyweight mounted to a cam. - Coiled spring.

Impulse couplingCam assembly of an impulse coupling is keyed to the magneto shaft.Impulse coupling body rotates with the engine.Coiled spring inside the impulse coupling links the cam assembly and body together.Eng. turn, flyweights on the impulse coupling contact stop pins on the magneto housing.Stop pins stop magneto shaft rotation, eng. continues to rotate and wind up the impulse coupling spring.Coupling body contact trigger ramp on the flyweight forcing the flyweight to off the stop pins.This releases accelerates the magneto speed and produce high voltage, retarded spark.

Impulse couplingProduces high voltage spark during starting process.Once eng. started, magneto speed fast enough to produce high voltage on its own.Centrifugal force pulls the heel of the flyweights outward so no longer contact the stop pins.Impulse coupling disabled.Sparks back to their normal advanced timing.

Induction vibrationSupply pulsating DC to primary winding.Pulsating current flows will be induced into the secondary winding.The faster the pulsating DC, the greater the current induced for starting.The frequency of the pulsating DC is determined by the induction vibrator.Vibrator operates when switch is engage or start to produced pulsating current. Magneto breaker closed current flow to the ground.When open pulsating DC flows in and produce high voltage pulses to distributor then to spark plug.Frequency of pulses produced by the vibrator coil allow multiple sparks to be produced at a spark as long as point remain open.As the points close, pulsating current routed to ground. This process is repeated each time breaker points open and pulsating current flows to the primary winding.As engine started the starter switch is disengaged stop the current flow to the induction vibrator.

Shower of sparksWorks the same as the induction vibrator system.Except its has a set of retard breaker point to provide retard spark when engine is cranked.Located in the left magneto together with advance points.Start position, a relay in the starting vibrator grounds the right magneto and provides pulsating to the left magneto.Both retard and advance are grounded, points must be open to allow current flow to the primary winding.Engine started switch to both position, battery power is removed from the starting vibrator.Right magneto ungrounded and retard point disconnected.Both mag. operate normally to provide advance spark.Components used are solid state no maintenance required.If fails removed and replaced.

Booster MagnetosNot in use on modern a/c.Consist of separate magneto and located in the cockpit.Hand operated by pilot during starting.Voltage generated by booster magneto supplied to a special distributor that directed a spark to the cylinder just behind the one that normally fired by the engine driven.If firing order is 1-3-5-7-9-2-4-6-8.Booster magneto supplies spark to cylinder no. 1 when eng. driven mag. to fire cylinder no. 3.This retards the spark for ignition.

Ignition SwitchTo provide means of controlling when ignition is switch ON and operating.Ignition located in the cockpit, operated by pilot.Switch OFF contact closed. ON contact open.Ignition switch is wired in parallel with the breaker point.OFF position contact closed to ground the circuit. Prevent magnetic field in the primary winding from collapsing and induced to secondary winding.ON position contact open. Breaker point interrupt primary current flow to produce the pulsating current to create spark.Ignition switch lead which connects the switch and the primary circuit referred to as P-lead.P-lead consists of several strands of cooper wire are shielded to help reduce radio interference.

Ignition switch conts.Switch controls both magnetos.Has four position: OFF, LEFT, RIGHT, and BOTH.OFF position, P-lead on both mag. are grounded.LEFT position, left mag. operates and right mag. grounded.RIGHT position, right mag. operates and left mag. grounded.BOTH both mag. operate simultaneously to produce spark.Operational check should follow manufacturers checklist.Start the engine then accelerate to 1,500 and 1,700 rpm.Engine stabilizes, place ignition switch from both to : - Left :- right mag grounded slight drop in eng. rpm. - Both :- rpm should return to normal value. - Right :- left mag. grounded slight drop in eng. rpm. - Return back to Both position when completed. - Engine drop to zero while operating either left or right a short exists between mag. and ignition switch.From Both to Off momentarily eng. should quit because mag. are grounded.If eng. fail to cease P-lead or faulty ignition switch. Stabilize eng. at grd. idle before shutdown.

Magneto OverhaulMost magnetos are reliable and trouble free.Remain on an engine until the engine is overhaul.Often sent to manufacture or certified repair station for overhaul.Any overhaul to be carried out strictly refer to manufactures overhaul manual.

Disassembly and CleaningDisassemble and clean a magneto as outlined in manufacturers maintenance manual.All components should handle with care to avoid damage.Soft iron keeper should be placed across the poles of magnet to retain its magnetism.Cleaning magneto components only with approved solvents and cleaning methods.Most manufacturers specify that acetone to used for cleaning grease and carbon track from capacitor and coil.

InspectionWhen overhaul the magneto certain parts or components required to be replaced.Components normally replaced during overhaul: - Breaker point. - Capacitor. - Bearing. - Distributor block and rotor. - Lock nuts. - Gaskets. - Cotter pins. - Self-locking nuts or screw. - Oil seals.Before discarding the items its good to check/inspect them for evidence of malfunction and excessive wear.

Magnet CaseInspect magneto housing for crack. Other area that prone for crack are:- Mounting flange.- Bearing surface.- Area around threaded holes.- Mating surface.Any crack found on the component replace the item.Sign of pitting or corrosion. (light corrosion remove it, if excessive replaced). To prevent corrosion, mag. cases have one or more drains and a vent.Drain prevent condensation in the mag. case. Vent allows the corrosive gases to escape and helps to cool the magneto.

Rotating MagnetBoth magnet and magneto shaft to be inspected for physical damage and wear.Magneto shaft required dimensionally check to determine it is within serviceable limit.Magnet to be check using magnetometer or gauss meter for it strength.If lost its magnetism, it may be remagnetized by special equipment.

Gear assemblies and Bearing Distributor drive gear, cleaned and inspect for: - excessive wear. - cracks. - broken teeth. Excessive backlash or play in the distributor drive gear is cause for rejection. Magneto shaft bearings and races to be replaced during overhaul. Some manufactures permit its to be reuse again but must be inspect and service as prescribed by the manufacturer.

Magneto coilInspect insulating material for crack and burn mark.Check for coil lead for general condition and security.Check for continuity and resistance in each winding.Can be done by ohmmeter or multimeter.

Breaker assembly.Breaker point subjected to intense wear.Replace with a new set whenever a magneto is overhaul.Before discarding, check the breaker points.If points are badly pitted, it may indicate the capacitor is not functioning.

DistributorDistributor can be reuse, if permits by the manufacturer.Must inspect the distributor block and rotor for crack, carbon tracks, soot and sign of arcing.Check for excessive play by insert a specific size of drill between each of the gear teeth.Should fits nicely.No sign of cracking or arcing, the block should be tested with high tension harness tester for any leakage or shorts.For reassembly coat it with wax to prevent arcing as per manufacture instruction.

CamMade of either a solid piece of metal or phenolic compound.For metal cam can be reused if dimensionally checked within limit.Phenolic cam to be discard and replace with new cam.

Assembly and Internal timingMagneto components that had been cleaned and inspected can be reassemble IAW manufactures instruction/manual.And also internal timing process as manufacturers timing instructions.Mag. internal timing performed during assembly and carried out in bay and bench check.For Bendix magneto, case halves are assembled then carried out internal timing cx.But for Slick magneto carried out internal timing first then only put the case halves together.Do not put on force during assemble the case halves together, you could damage the distributor rotor.

Bench testingAll magneto that has been reassembled and internally time should be tested.Test carried out on the magneto test stand.Test stand includes a variable-speed drive motor, tachometer and spark rack.Mount a magneto on the stand.Check the gap on the spark rack. (slightly bigger than spark plug less resistance than in the cylinder)If gap too wide, excessive voltage build up could damage the coil and distributor.Connect all the high-tension harness.Verify the direction of the rotation before engaging the motor.From slow speed to high speed there should have sparks on the spark rack.If poor performance could be improper timing, weak capacitor or weak magnet.

Magneto to Engine timingPerformed when installed on the engine.When timing two magnetos to an engine, its could be either synchronized or staggered ignition.Synchronized ignition timing: - Magnetos are timed to fire both spark plugs at the same time.Staggered ignition timing: - Requires the two plugs to fired at slightly difference time. - Spark plug nearest to cylinders exhaust fired first. - Reason Fuel/air mixture become diluted by the exhaust gases and tends to burn more slowly.

Flange-Mounted magnetoSpecial tool required are: - Time-rite indicator. - Time light (synchronizer).Set piston no.1 cylinder to TDC on compression stroke (with spark plug removed).Attach the magneto to the mounting and secured.Attach timing light to each magneto.Rotate magneto until timing light just come on and tighten bolts (ensure propeller not move).To verify the timing, rotate propeller opposite direction timing light off and turn prop forward again light come on again.

Base-Mount magnetosFound on the radial engine and coupled to the engine accessory drive with vernier coupling.Special toothed coupling with slotted rubber disk sandwiched between two gears with different number of tooth.Adjustment carried out by disconnecting the coupling and rotate the rubber disk to the necessary number of slots. Operational checkAfter reinstall the magnetos an operational check to be done.Ensure P-lead is connected and also spark plug leads.To verify the entire ignition system is properly function, the operational check have to be carried out.Run the engine using manufacturer stating procedures.

Magneto MaintenanceCommon maintenance need to be performed are; - Inspection and examination of the magneto. - Integrity and security of the case. - Condition of the points. - Capacitor and distributor. - Magneto to engine timing. - Operational check. Magneto case. - Check for crack, replace if crack. - Corrosion removed and painted. - Pitting exist badly replace the case.. - Vent clear from obstruction if clog trap nitric acid gases will corrode the internal part of the magneto.

Breaker pointTo check points P-lead to be disconnected.Bear in mind that magneto is life (hot) regardless of the ignition switch position.New breaker point (A) have a smooth, flat surface with a dull gray, sandblasted or frosted appearance.After few hours of operation (B), slightly wavy appearance.Excessive metal transfer the point (C) become pitted or coarse grained.Replace breaker point.Excessive wear can shift the internal timing. Point worn out, open early and advance the spark and open for longer period and decrease in spark intensity.

Breaker assemblyOil presence on the point no effect to the operation.It will attract contaminating metal and dirt particles that can lead to burning and pitting.Remove oil from the point by insert apiece of clean hard cardboard between the two contacts.Never slide the cardboard, particles could leave behind and contaminate the point.Check the spring using a small spring scale.Attach to the spring arm and carefully pulling the contact points apart.Open not more than 1/16 in. to prevent damage to the spring.Spring tension below limit could cause the points float or bounce at high speeds and will loss of spark energy.Breaker cam checked for wear and damage such as pitting or distortion.Excessive wear could lead to point open late and retard the ignition.Open at shorter time and decreases the spark intensity.

CapacitorExcessive point wear caused by defect capacitor.Checked capacitor using condenser tester.These tester use AC voltage to check capacitors capacity and DC voltage to check for electrical leakage.Capacitor capacitance value too low breaker point will burned and pitted.

DistributorDistributor block and rotor check for crack, carbon tracks ,soot and sign of arcing.Crack block and rotor provides low resistance path to grd. for secondary voltage.Small crack requires replacement.

SealsPresence of oil in a magneto indicates oil seal fail.Oil conductors electricity, anytime oil is found in a magneto, must removed and disassembled, cleaned and inspected.Change seal as required.

TimingMagneto to eng. timing should be checked as part of a 100 hrs and annual inspection.If unsatisfactory during operational check, mag. to eng. or internal timing to be carried out.Anytime breaker assembly is removed for cleaning or replace, internal timing must be readjusted.Also magneto to eng. timing.

Engine Analyzer Monitored engine performance to aid in diagnosing eng. problem. System tracked ignition system performance and eng. vibration. Displayed them on the an adaptation of a laboratory oscilloscope.Unit can be portable and permanently installed. Today , CHT, exhaust gas temp. gauges primarily used as indirect indicators of ignition system.

Ignition HarnessIgnition system to be efficient.Must be delivered to the spark with minimal loss.Purpose to deliver high voltage to spark plug through low resistance elect. path and keeps leakage to a minimum.Harness consist of 4, 6, or 8 individual ignition leads.One end to a receptacle on a magneto and the other end to spark plug.

Harness ConstructionConductor use in spark plug lead is stranded wire or single coiled.Encased in one or two layers of rubber or silicone insulation.Covered with braided metal shield.Insulation prevents current leakage.Shielding to reduce radio frequency by collect and channels high frequency electromagnetic to ground.Protect shielding from chaffing and moisture, the shielding is impregnated with a silicone material.

Ignition Harness

Ignition Harness

Harness constructionTwo different size used in a/c ignition harness, 5mm and 7mm.5mm commonly used and 7mm for older a/c.Modern ignition leads ends can fit 5/8-24 shielded spark plug or - 20 all weather spark plug.(A) Ignition leads are terminated with straight terminals or bent to facilitate installation.Sharp bend causes stress and weak point.(B) 7mm lead require large bend radius, angled terminal are available with 70, 90,110 and 135 elbows.(C) 5mm straight terminal can be bend if bracket is installed to hold at a safe bend radius.

Harness constructionTerminal ends on ignition leads consists of a silicone rubber nose that slip into a spark plug body.Referred as all weather terminal, prevent water from entering on top of spark plug body.Terminals are crimped onto an ignition lead and the coiled wire screws over the end of the terminal.Replaced if become damage.

Harness constructionOlder terminals with a phenolic or ceramic insulator tube referred to as a cigarette.Terminal contains coiled spring extends beyond the end of the insulator tube.Provide positive electrical contact between ignition lead and spark plug.

Harness constructionCigarette-type terminal ignition lead insulator have to be cut at the back of it to allow wire to protrude.Conductor wire is then fanned out to secure the wire to the cigarette and provide good contact.Magneto end leads utilize crimp on type connector.Exact type of connector depend on types used.Another method, connect ignition leads to a distributor block with cable piercing screws.All installation to ensure braided wire to be secured at both ends. (grounded).If not, radio interference could occur when engine running.

MaintenanceMaintenance consists of repairing, replacing terminal ends or chaffed lead.Information of replacement procedure and tools used as manufacturer instruction.Replacement can be made by single harness or entire set.If come in set, the harnesses are precut to the proper length. Pay close attention to wire markings that indicate the distributor terminal to spark plug.Eg. 1T indicate a lead cut to length for top spark plug for no. 1 cylinder.Routed and secure all lead around the exhaust and not interfere with flight control.Ensure shielding properly grounded, added second layer of shielding as required.

Installation tools.

TestingAnytime a conductor carries high voltage energy and is installed near a conductive mass.The insulation around the conductor is exposed to what is known as high voltage corona.Repeated exposure can cause dielectric strength of the insulation to breakdown.Increase the possibility of arcing. To detect breakdown in the insulator have to use high tension harness tester.Tester applies 15,000 volts DC to the lead and then uses a micro-ammeter to detect the leakage.Another type use is light indicator or by inability spark to jump an air gap in the tester.

Spark PlugThe end result, spark that ignite the fuel/air mixture in the cylinder.The construction and operation of a spark plug is simple but demands placed on ignition systems are high.If eng. operate at 2,100 rpm, approx. 17 separate ignition events occur per second.About 20,000 volt spark jumps the air gap.Its must be able to operate in temp. of 3,000F or higher and pressure of 2,000 psi.

ConstructionMost spark plugs are similar in appearance.Difference do exist among spark plug types.Engine manufacturers specify the type of spark plugs in used.Consists of three major parts; - Metal shell - Ceramic insulator - Electrode assembly

Construction conts.Metal shell: - Provides support for the internal component. - Provides an electrical path to grd. for braided shield of the ignition lead. - Shells are threaded at both ends. - One end allow an ignition lead to be attached to spark plug, referred to as terminal or shield threads - Opposite end to be screwed into a cylinder. - To facilitate the installation and removal a spark plug a hex or six-sided nut is cast on the metal shell.

Spark Plug

Ceramic insulator: - Prevent high voltage current flowing through a plug from arching to ground. - Insulator consists of two sections; One section extends from tip of the center electrode up to the terminal contact. The other section from top of spark plug barrel and extends downward to overlap with the first insulator section. Nickel gaskets between plug shell and insulator prevent escape of high pressure from the cylinder.

Electrode assembly: Consist of a terminal contact, resistor, glass seal, center electrode and outer electrode. - Terminal contact where the ignition lead makes contact with the spark plug. - The opposite end of the thermal contact is a small resistor. - Resistor is to prevent capacitance afterfiring. - Capacitance afterfiring is the process which electrical energy is induced into the ignition shielding when current flows through an ignition lead. - Once the electrical potential in the shielding builds, stored energy is released as surge across the air gap of the spark plug. - This lengthens the spark duration and accelerates wear of the plug electrodes. - By inserting a resistor in a spark plug, the stored voltage in the shielding is dissipated so it can not jump across the plug gap. - Resistor has a value of 1,500 ohms.

Conts.

- Material used to construct the center and outer electrodes varies depending on the types of electrode used. - Massive-electrode spark plug, the outer or grd. electrodes made of nickel alloy and center electrode from nickel-clad copper. - Fine wire electrode plug, the grd. electrode made of platinum or iridium and center electrode from silver. - The ground and center electrode on spark plug are separated by an air gap of a specific width. - The size of the air gap determines the amount of resistance a spark must overcome before it can jump the gap. - If size of an air gap not adjusted properly, the intensity of the spark produced will also be incorrect.

Shell Thread ClassificationSpark plugs are classified according to the size of the shell threads that screw into the cylinder.Plug threads are either 14 mm or 18 mm.Most modern a/c use 18 mm spark plug.The terminal come in two sizes; either in 24 thread or in 20 thread.Both sizes are used in a/c but in 20 is the size of choice. in 20 thread is referred as all-weather spark plug.All-weather spark plug the ceramic insulator does not extend to the top of the plug shell.This leave a room for the silicone grommet to form a watertight seal at the terminal.

Spark Plug ReachReach defined as the liner distance from the shell gasket seat to the end of the shell threads or shell skirt.Spark plug are available either long reach or short reach.On 14mm plugs, long reach dimension is 12.7mm or in.; short reach is 9.53mm or in.On 18mm plugs, long reach dimension is 20.64mm or 13/16 in.; short reach is 12.7mm or in. Spark plug installed in an engine, the end of the threads should be flush with the cylinder heads inside wall.Install a spark plug with the wrong reach, it will either extend beyond or recessed in the cylinder.

For example:- If long reach spark plug is installed where a short reach plug is required; (A) - end thread of the plug will be exposed to the heat of combustion. - exposed thread will susceptible to carbon buildup, make it difficult to remove. If short reach plug is used in place of long reach plug; (B) - thread in the cylinder head will exposed to combustion gases and possible damage.

Heat Range Refers to the spark plug ability to conduct heat away from its firing tip to the cylinder head. Classified as: - Hot, normal or cold plugs depending how well they transfer heat. Primary factor in determining a plugs heat range is the length of the nose core. (A) Cold plugs short nose core large contact area between the ceramic insulator and plug shell. - Large contact area allows heat to conduct readily to the cylinder head. (B) Hot plugs long nose provide little contact area for heat to dissipate.

Heat RangeAll a/c engines are certified to use spark plug with a specific heat range.General rule, high compression engine operates at high temperature and use cold spark plug.Lower compression engine operates relatively low temperature and use hot spark plug.If hot spark plug use on engine required cold spark plug the hotter operating temperature of the plug could lead to preignition or engine run-on.Cold spark plug is installed in a cold running engine, plug become fouled with unburned carbon and lead deposits.Some circumstances require to use spark plug that may not be in the recommended heat range. - e.g. :- Engine run on 80 octane avgas, required a hotter plug when use 100LL avgas due to higher lead contain. - Higher lead level could cause lead fouling in the cooler spark plug.

ServicingManufacturers recommend the removal of spark plug for inspection and servicing at regular intervals.100 hrs inspection.Intermittent engine running cause by defect plug.Badly fouled plug no ignition will occur.

Removal

Before remove a set of spark plugs, you must first remove the ignition lead. When removing, best hold the ignition lead with one hand and then loosen the terminal nut. Once the terminal nut fully back off, pull the terminal end straight out of the plug. Tilting a lead terminal can crack or damage the insulator. Remove the spark plug with deep socket. Ensure the socket is squarely over the plug hex and loosen it. Tilting the socket could damage the plug ceramic insulator. Plug is removed and placed in a tray. Easy to identify from which cylinder number and position (top or bottom).

Visual InspectionVisual inspection of spark plugs reveals about the efficiency of an engine.If plug covered with a dull brown deposit and little buildup in the firing cavity, normal combustion.Firing cavity is filled with hard, bead-like deposits, excessive lead fouling. Fouling must be investigated and corrected. - Causes include improper fuel vaporization, low cylinder head temperature or improper plug heat range. - Should install plug with a hotter heat range. Covered with a soft black sooty deposit, indicate a problem with carbon fouling. - Cause of rich mixture or leak primer. - If deposit appear on the exhaust stack also cause by excessively rich mixture.

Visual inspectionOil fouling is another type of contamination found on spark plug. - cause by broken or worn piston ring and worn valve guides. - appears as blackened, slippery coating on a plugs electrodes. - serve enough an engine have to be removed and repair. Existence of hard glaze on plug, indicates that sand was ingested into the engine.In chamber some of the silicates in sand melt with the heat of combustion. - as molten silicates cool, they form a glass-like coating on plug. - silicon glaze is non-conductive at low temperature. - high temperature, glaze become conductive and lead to spark plug misfiring. - sand ingestion is the result of poor filter and induction system leak.

Visual inspectionIf the electrodes on a spark plug are worn to approx. half their original size, it should be replaced.Excessive wear can distort the shape of both the center and ground electrodes.Abnormal wear on plugs electrodes is an indication of fuel metering problems, cause by; - excessively lean mixture. - induction air leak. - partially clogged fuel nozzle.Beside check for plug wear, should examine the ceramic insulator for crack.If crack found replaced with new plug.If plug dropped on hard surface, automatically discarded.

CleaningClean spark plug with approved safety solvent to remove oil, grease, and other soft deposit from the plugs exterior and firing cavity.Once degreased, dried with compressed air.Lead and carbon deposits removed with a vibrating cleaning tool.- use proper cutting blade.- hold spark plug directly over the blade.- slight back and forth motion over the blade will chip away the lead deposits.

CleaningTo complete the cleaning process on the plug, an abrasive grit blasting cleaner can be used.Adhere to the manufacturers instruction concerning grit type and air pressure.Silica abrasive is not recommended because it can contribute to silica fouling.When using grit blast cleaner; - move plug in circular motion. - limit to few seconds only. - this help to prevent excessive erosion especially on fine-wire spark plug.After blasting, blow out all traces of the grit with clean air.If used wet-blast method, dry plug in an oven to avoid rusting.When clean and dry, inspect them with light and magnifying glass. Clean plug thread on both end with a steel brush or soft bristles to remove any carbon or corrosion.

GappingGap between the center and ground electrode to be checked and adjusted as required.Gap of 0.16, do cx. with round wire gauge of 0.15 and 0.19 in. (go or no go) If gap too big, the ground electrode may be forced inward to reduce the gap.Use proper tool and manufacturers instructions to prevent damage to nose ceramic or electrode.Adjusting gap on a massive-electrode plug using a special gapping tools. - ground and center electrode must be remain parallel.- plug must be clamp to the tool.- ground electrode is moved inward using a movable arm or threaded adjusting arm.- adjusting slowly, prevent closing gap too much.- any attempt to enlarge a gap on a massive-electrode plug may cause damage to insulator or electrode

GappingDo not leave the wire gauge between the two electrodes.If left behind will damage the insulator when apply load during gap adjustment.Fine-wire spark plug with electrode of platinum and iridium are extremely brittle and easily broken, handle with care.Avoid closing the gap too much. Testing Once a spark plug is cleaned and gapped, it should be tested. Use special testing equipment, provide voltage to fire the plug in rapid succession under pressure.

InstallationWhen installing plugs you should rotate them from where the plugs were originally installed.This promotes even plug wear and extends plug service life. (metal transfer from one electrode to another). Polarity Each time rotating magnet passes the natural position, polarity of current changes. Spark produced by a magneto alternate in polarity. Engine with an even number of cylinder, each spark plug fires with same polarity every time. If no. 1 cylinder spark jump from ctr. to grd. electrode. And next cylinder in firing order no.4 , spark will jump from grd. to ctr. electrode. When the polarity of sparks on a plug do not change, one electrode looses metal relative to the other one.

PolarityPlug fire positively, the ground electrode looses more than the center electrode.When plug fire negatively, the center electrode wears more than the ground electrode.Spark plug rotation will balance the electrode wear and increase the service life of a plug.Swap the plugs from top to bottom.The reason is lead and other impurities produced during combustion process tend to precipitate to the lower plug. Help equalize plug wear.

PolarityBefore installing the plug, applied anti-seize compound to the shell threads.Applied the correct type supplied by spark plug manufacturers.Apply on the second thread from the firing end.Never put at the firing end, it could run down over the electrode.Replace gasket whenever install the plug, once harden gasket loses its ability to seal.

Reciprocating engine starting systemEarly day of aviation to start a/c engine by hand propping.Problem in cold weather, thick oil hard to turn.Engine got larger make more difficult and dangerous.

Types of Starting SystemInertia Starter Direct-Cranking Starters (Electrical Starter)a.Small engine startersb. Large engine starters

Inertia StarterInertia Starter Hand crank to spin flywheel through a step-up gear drive assembly.When high speed, hand crank removed and the starter engage.The kinetic energy of the spinning flywheel is converted to mechanical energy to drive engine crankshaft.A torque overload clutch located between the flywheel-ratchet jaws prevent damage to the engine or starter when its first engaged.

Direct-cranking startersUsed electric motor to spin the flywheel for easier engine starting. However hank cranking feature still applied if insufficient battery power.This type widely used on all types of recip. engines. This provides instant and continual cranking when energized.This type used series wound dc motors to drive the starter.This type is capable of producing a high starting torque.

Direct-cranking startersRelatively constant voltagethroughout a starting cycle.Drawing out very high current at the start of motor rotation.Do not contain fuses or circuit breakers because it will tripped circuit breaker or blown fuse each time the engine started.

Direct-cranking startersSmall engine startersUsed small series engine would electric motor with small gear.Small gear meshes large gear and part of an over-running clutch and drive pinion or drive gear.Engaged by either a hand-pulled cable or a solenoid which engages a shift lever.Hand-pulled cable attached by cable /rod to tee-handle.Electrical switch activates a solenoid.When started over-running clutch spinning until tee-handle or starter switch released and return spring pulls the pinion away from the starter gear.

Small engine starters

Direct-cranking startersAnother type of direct cranking used Bendix driveas used in automobile. Consist of :Drive spring.Drive pinion.Drive shaft.Helical splines.

Direct-cranking startersOperation When starter switch is closed the starter spins thepinion through drive spring. The pinion movesforward on the helical splines and engages theteeth on the engine flywheel and turn the engine.When the engine started the flywheel gear spindrive pinion faster than the starter motor.This forces the pinion back along the helicalsplines until it engages from the flywheel.

Bendix driveas used in automobile

Direct-cranking startersTeledyne-continental starterStarter mounted on the side.Starter rotate the worm gear.Worm gear permanently meshed worm wheel.Clutch spring attached to the worm wheel.Worm wheel rotate it tightens the spring around a knurled drum on the engines starter shaft.When gets tight enough, starter shaft begins to rotate.Shaft gear then rotate the crankshaft gear and rotate the c/shaft.

Teledyne-continental starter

Direct-cranking startersAs crankshaft spin faster then the starter gear shaft causing the clutch spring to release the knurled and disengaged.The generator drive pulley is mounted on the end serves as generator drive shaft.

Direct-cranking startersLarge engine startersRequired to turn over a high horsepower engine and therefore employed reduction gear assembly.Consisting automatic engaging and disengaging mechanism houses as a single unit.Reduction gear motor shaft converts motors high speed low torque to low speed high torque.

Large engine starters

Direct-cranking startersMotors pinion drives the intermediate countershaft assembly.And rotate the sun gear.Sun gear then rotate the planetary gears.Therefore engaging the starter jaw to the engine.When the engine has started the return spring push the starter jaw to the rear and disengaged the jaw from the engine.

Large engine starters