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I Magneto Ignition

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I MAGNETO IGNITION -FOREWORD - Ignition service within a relatively few years has be- come a field for specialists. The training, skill and gen- eral knowledge of the service technician are the out- standing characteristics of the progressive service busi- ness. As a consequence frequent requests are received at the factory for fundamental information, prepared especially for study and reference in a particular service field. In providing a discussion of the principles osmagneto igni- tion, considerable time has been devoted to the review of magnetism and electricity, after which an analysis of ignition requirements leads to the description of various ignition systems, their development, application and impulse coupling adaptations. The final section deals with magneto service in a general way, no attempt being made to describe specific service operations as applied to individual units, but rather to offer suggestions toward the establishment of efficient service practices. It has been found impossible to cover the entire field of magneto ignition, or even to deal with individual topics on an exhaustive basis. The range of special applications and installations is so great that many are not even men- tioned. Especially is this true of the older ignition sys- tems, which due to changeovers are encountered infre- quently in the field. COPYRIGHT 1966 BY FAIRBANKS MORSE BULLETIN SI3-23 PRICE $2.00 @ Colt Industries ENGfNE ACCESSORIES OPERATION a BELOIT, WISCONSIN 53511 Page 2 Engine Accessories Operation TABLE OF CONTENTS Page I'age FOREWORD ....... ..... 1 SECTION SIX-APPLICATION OF MAGNETO IGNI- TION ...............32 SECTION ONE-INTRODUCTION ..... 3 I3asic Requirenlents ...........32 Definition of Rlagneto ......... 3 Practical Considerations .......... General P11rpo.s~of A.1agneto.s . ..... 3 Single Cylinder Rng-incs .......... The Magneto Asqembly .......... 3 Vulti-Cylinder Engmes .......... Magneto Engineering ..... ...... 3 Magneto Spark Interval .......... Manufacture of Alagl~etos ......... 3 Unequal Spark Iiltervals .......... 3lagnetoService ...... .....4 Brealier Cam Contorlr .......... The Skilled Technician .... ...... 4 Magnetic Rotor Poles ........... Future Developments ........... 4 Carbon-Bn~shDistribution ......... Jump-Spark Distribution .......... SECTION TWO-MAGNETISM & ELECTRICITY . 6 Sealed and Ventilated Units ......... Aa~licationof F~lndamentalTheory ...... 5 Coil Clil)~ant1 I.t.atl l{otlr; ......... 31; netivn . ......... 5 Rotntion of Magneto ........... &lofecular Theory of hiabetism ....... 5 Magneto Elountings ........... Types of hlagnets ... ....... 5 rot.^ Drive Arranpnlents ......... Physical Shapes of permanent Gagnets ..... 6 Flywheel Alngnetos ........... Demagnetization . ......... 6 Oscillator Alngnetos ........... permanent k~agnedbfate~als ........ 6 hlanual Spark 8dvance .......... Stability of Alnico h'lagnets . ....... 6 Automatic 8 ~arl;Advance ......... hiagnetic Characteristics of teei is ....... 7 Contr0l1ing~~nifionSpark:idvi~nce ...... Development of theHysteresis1,aop ...... 7 Ignition System Wiring .......... Significance of the Hysteresis Loop ....7 Primary Ground Swif.chcs ........ hlagnetic Attraction 6: Repulsion ....... 8 RadioShielded Ignition Systeli~ ....... Magnetic Field . .......... 8 Two-Spark Xlngnef-os ........... Magnetic Field ~tren~t'h.......... 8 Dual Ignition . ........ Magnetic Circuits ............ 9 Eight & Twelve ~ilinierunits ........ F:lectrjcity . ............10 Use of hlagnefos ............ Electrlc current; ..........11 Electric Potential (voltage) .........11 11 SECTION SEVEN-IMPULSE COUPLINGS ... Resistance .............. General Purpose ... , ....... Ohm's Law ..............11 Types of Impulse douplings ......... Resistances in Series ...........11 Description of Operation .......... Resistances in Parallel ..........11 Single Pawl Couplings .......... The \?heatstone Bridge ..........12 Twin Pawl Cou lings ........... Electric Circuits ...........12 Coupling Pawl gperation ........ Klectro-blagnetic F'ield ..........13 Spring-Loaded Couplin hwis ........ Field Surrounding a Helix .........13 Conlbined Drive Gear Bf Couplin ....... Inductance ..............13 Aflanually-Engaged Impulse ~ou$ings ...... 14 Transforn~ers . .......... Impulse Coupling Drive Springs . , ..... Spark or 1nduc~on'~o~l.......... 14 Impulse Coupling Spark Retard ........ Electro-Magnetic Induction ......... 15 Location.of Co~lplingShell Drive Lugs ...... Eddy Currents . ...........16 Relnovnl of Im tilse Coupling ........ Laminated ~ssembjies ..........16 Reassembly of fmpolse Coupling ....... Capacitance .........16 Inductive and R'on:Inductive Condensers .....17 Leakage Current .........17 SECTION EIQ3T-MAGNETO SERVICE PRACTICES Measurement of ~i'~hvoltage ........ 17 Magneto Service ............ Magneto Field Service ......... SECTION THREE-IGNITION REQUIREMENTS . 19 Testing the Ignition S ark ......... Internal Combustion Engines ........19 Testing the Magneto &ark ......... Compission-Ignition Engines ........ 19 Carbon Brushes . ........ Spark-Ignition Engines ..........19 Field Service of Breaker ~oin&........ Two Cycle Engines ........... 19 Field Lubrication . ........ Four Cycle Engines ...........20 SubstitutionT~tsfor~oii&~ondenser..... Importance of Ignition ......20 Impulse Coupllng ............ Ignition Spark ~imin~-&gihe speed ......21 Shop Service ......... Spark Plugs ...........21 Essential Shop kqu0ipn;ent ......... Spark Plug ~lecirodes............ 21 Preliminary Cleaning ........... Hot-Normal-Cold Plugs .........22 Preliminary Tests . .......... Engine Speed & Compression ........22 Cleaning l3reaker ~oin'ts.......... Breaker Point Assembly Wear ........ SECTION FOUR-EARLY IGNITION SYSTEMS . 23 Edge Gap Adjustment .......... Engine Ignition Requirements ........23 Ma net0 Bearings ............ Low Tension Ignition Systems ...23 ~alf eari in ........... Low Tension Magneto Ignition .......23 Cleaning B% ~karings .......... Relubricating Ball Bearin9 ......... SECTION FIPE-MAGNETO DESIGN & CONSTRUC- Replacement of Bdl Bearings ........ TION . ............24 Sleeve Bearings . .......... General ~lassification. ......24 Replacement of ~1eeve'~earin~s........ Shuttlewound Aimature~a'~ne'tos ...24 Needle Bearings ....... Rotatin Primary Coil Variation ...25 Servicing ~istributbr~otors & ~iscs ...... Rotary fnductor l\Iagneta .........25 Timing Gears . .......... Reci rocating Inductor Magnetos .....26 Removal of Rotor pinion .......... he kotating Magnet ~Iagneto\. ........ 26 Leakage Paths . ......... Description of Operation ..........26 Corrosion Caused by oxidation ........ Oscillograph Analysis ...........27 Overhaul of Oxidized Units ......... The Magneto Housing .........28 Testing Magneto Coils .......... The Breaker Point ~ssembl~........ 28 Condenser Testing ............ Contact Point blabrial ..........29 Magnet Charging .... ..... The Magnetic Rotor ..........30 The Synchroscope ............ The High Tension ~oii.......... 31 Spark Gap Assemblies .......... Condensers ....... ...... 31 Replacement Parts ........... Engine Accessories Operation Page 3 SECTION ONE INTRODUCTION DEFINITION OF MAGNETO primary winding and the interlocking magnetic field. A dynamo is any machine which transforms mechanical energy into electrical energy. Under this definition there (b) Voltage transformation, which takes place in the are several distinct classifications, a magneto being the interlocking primary and secondary windings of particular type of dynamo which uses permanent magnets the coil, the high voltage surge being caused by LO establish its magnetic field. breaking the primary circuit at the point the pri- mary current reaches its maximum value. Strictly used, the term magneto applies only to the current-generating portion of the ignition unit and does (c) Spark distribution, which consists in conducting not include the transformation of the low voltage primary the high voltage secondary surge to the desired current to the high voltage secondary ignition spark ignition circuit at the correct intervals. In stand- discharges, nor to the distribution of these spark dis- ard units for single cylinder engine applications, charges. As examples of this interpretation, the current- this function is unnecessary. producing unit of the old style crank telephone or of the electric t~ghometeris also known as a magneto. In the ignition field the technical definition is not commonly observed and it will be assumed throughout the following discussion that the magneto is the entire self-contained unit as it functions to supply the ignition spark discharges. GENERAL PURPOSE OF MAGNETOS Modern magnetos are compact, self-contained units designed and constructed specifically for the production of controlled electric spark discharges of adequate strength to meet the ignition requirements of internal combustion engines or of similar applications. Entirely independent of any exterior source of electrical or chemical power, a magneto ignition unit depends solely Figure 1-Funct~ons of a Magneto upon mechanical energy, which can be supplied, for example, by hand cranking. This characteristic is of vital importance in remotely located or infrequently MAGNETO ENGINEERING operated installations, and of considerable convenience The design of magnetos is influenced by a number of in many others. important factors, among which are the requirements of Another advantage based directly upon the fact that the 'application, the performance of the magneto, the magnetos operate as a
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