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Fit high-energy ignition to your car Is your car still limping along with outdated Kettering ignition? What? You are still cleaning points, adjusting the dwell, checking timing and all that automotive drudgery? Now you can fit this High Energy Ignition System and forget those tuneup hassles. By LEO SIMPSON & JOHN CLARKE These days the vast majority of new cars are fitted with breakerless ignition as standard equipment and they perform much better for it. In fact it is safe to say that with the lean fuel/air mixtures now used in modern vehicles, they probably wouldn't run at all if they did not have a high energy ignition with long spark duration. But what about all those tens of 32 SILICON CHIP thousands of older vehicles which still rely on the old Kettering ignitions? They can benefit greatly by being fitted with electronic ignition, whether the points are retained or the system is converted to breakerless operation. What are the benefits? If you have an older vehicle without electronic ignition, you can obtain several benefits by making the changeover. You can get a little more power, slightly better fuel economy and smoother engine performance, particularly at idle and with four cylinder engines. But the main benefit is the greatly increased times between tune-ups. Once tuned up, the car will stay that way much longer than when Kettering ignition is fitted. With the Kettering system (ie, conventional ignition with the points switching the current through the coil), the ignition "tune" starts to deteriorate almost from day one. When you consider the much longer period between tune-ups and the fact that the engine stays "on song" for much longer, the overall benefit of better performance and ~ Ideally, the high energy ignition module should be installed in the coolest available spot underneath the bonnet. This location in a Mazda 323 is suitable. Use 12mm x No.10 selftapping screws to secure the module to the fender. better fuel economy is very considerable. Add in the benefit of better starting on cold days or when the ignition system has been drenched and you're way ahead. If your car has been modified to increase its engine power, you should have a "high energy electronic ignition" system, as presented here. It will give equal or better performance than a so-called "sports" coil and will also solve the problem of points which burn out in no time at all. The high energy electronic ignition system we present here can be used with the existing points in your car's distributor or you can go the whole hog and replace the points with an electronic breaker system. Why "high energy"? Modern cars need a high energy ignition system. Because they use relatively lean fuel/air mixtures to meet pollution standards, they need a longer spark duration to make sure the leaner fuel/air mixture actually burns completely. The way to ensure long spark duration is to make sure that the ignition coil stores a lot of energy; ie, to make sure that the current through the coil is high. That way, when a spark is initiated across a spark plug, it takes some considerable time to discharge the energy stored in the coil. Actually, the story is a good deal more complicated than that, as will be apparent as you read on. Another reason why modern cars need higher energy from their ignition systems is that, in general, modern engines deliver their maxim um torque and power at significantly higher revolutions than older engines. So while the Kettering ignition system may have been reasonably adequate for older engines the higher spark rate needed for modern engines means that considerably less energy is available, just when it is needed. Even for older engines, electronic PARTS LIST 1 PCB, code SC5-1-588, 1 02 x 59mm 1 diecast box, 11 0 x 30 x 63mm 4 6mm standoffs 3 solder lugs 1 grommet 1 T0-3 mica washer and insulating bushes 1 T0-3 transistor cover 1 eyelet/lug assembly (see text) Semiconductors 1 MJ10012 NPN power Darlington (Motorola) 1 BC337 NPN transistor 4 1N4761 75V 1W zener diodes ignition can deliver significant benefits because considerably more spark energy is available, at virtually all engine speeds above idle. For those readers who would like to know a little more about the workings of standard Kettering ignition, we suggest that you read the accompanying panel which explains what you need to know for the purpose of this article. Over the past twenty years or so, the staff at SILICON CHIP have had considerable experience with the design of electronic ignition systems for cars. In setting out to design a new circuit we knew we 1 1 N4002 1 A diode 1 MC3334P ignition IC (Motorola) Capacitors 2 0.1 µF 1 OOV metallised polyester 2 O. O1 µF metallised polyester Resistors (0 .25W, 5%) 1 x 4 70kQ, 1 x 56kQ , 1 x 22k!J, 1 X 1 OkQ, 1 X 2.2k!J, 1 x 3300, 1 x100Q5W, 1 x47!J5W Miscellaneous Automotive wire, screws, nuts, shake proof washers, solder, heatsink compound , etc . had to come up with something which offered significant advantages over previous designs. Ultimately, a microprocessorcontrolled engine management system is the real answer. It is specially programmed to control the timing of the ignition and the fuel injection and to do it in such a way that engine performance is greatly enhanced under all conditions. Short of going out and buying a new car though, you can't have it. As far as we know, there is no after-market "add-on" engine management system available for any car, anywhere in the world. In any event, we weren't going This is what the ignition module looks like when all the components have been installed on the printed board and then fitted into the diecast case. The diecast case serves as a heatsink for the switching transistor. MA Y 1988 33 1 ------- I I I r - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + 1 2 V VIA IGNITION SWITCH I I I I I I f I I I 41n I 5W 100!1 5W 2.2k 470k I I c, I I I ---HTTO DISTRIBUTOR I I ___lL I 330\l I 1N4002 05 I .01 22k 5 1--'......_.'IH,----, IN 02 BC337 IC1 ----=-H.... 7 OUTt-- MC3334PREF 3 4x1N4761 (75V 1W) POINTS POINTS CAPACITOR 0.1 56k - - - - : - -- - - - - - - - - - - ,- - . . - - - - - - - - + - - - - + - - - - - - + - - - - - - . . . _ _ _ . C H A S S I S 1 I.__ _ _ INPUT _CIRCUITRY _ _ _ _ JI .,. CASE HIGH ENERGY IGNITION SYSTEM SC5-1-588 0 ;-c 0 B VIEWED FROM BELOW Fig.1: the key components are the Motorola MC3334P high energy ignition integrated circuit and the MJ10012 high-power Darlington transistor. The Darlington transistor switches the heavy currents through the coil. The string of four zener diodes protects the Darlington against excessive coil volts if a spark plug lead becomes detached. for the ultimate. What we were after was a circuit that gave improvements over existing designs, whether it was in the performance delivered, reduced circuit complexity and cost, improved reliability or better compatibility with the various types of distributor now available. We believe we have achieved all of the aims just mentioned. The new circuit is less complicated, is easier to build and dissipates a lot less power so it should also be a lot more reliable than existing designs. Key parts from Motorola The new circuit is based on two key components specifically designed for automotive ignition by Motorola. They are the MC3334P high energy ignition integrated circuit and the MJ10012 power Darlington transistor. Elsewhere in this issue we give a run-down on the specs and application of the MC3334P but let us just touch on the main points now. First, the MC3334P is designed specifically to drive the MJ10012 power transistor (such long type numbers these beasties have). The MJ10012 takes the place of the ignition points and switches the heavy coil current. 34 SILICON CHIP Second, the ignition IC is designed to run at extreme temperatures, from - 40° right up to 125° Celsius (that's hot!). By contrast, most ICs for consumer applications are only rated for operation at up to 85° Celsius. Third, the IC is designed to operate over a wide range of voltages and incorporates transient protection on its inputs and outputs. That is very desirable for any electronic device working in the onerous environment of a car, especially under the bonnet. Fourth, the IC provides dwell extension so that a long spark duration is assured. We'll talk about dwell and dwell extension later. Well with all that magic built in, what did we at SILICON CHIP do in producing this design? Merely reproduce the Motorola circuit? Now how could you think that! Anyhow, it wasn't that simple. There is always a catch and in this case there were several. The first catch is that the MC3334P is specifically designed for distributors which have reluctor type pickups, as used in many standard electronic ignition systems fitted to new cars. So we had to adapt the circuit for use in distributors which have conven- tional points. That proved to be a tricky piece of design but we also went one step further and made sure that the circuit could be used with distributors having Hall Effect pickups. For this month though, we are only presenting the circuit for conventional points operation. Circuit description Now have a look at the circuit diagram for the ignition system. Besides the MC3334P and MJ10012 devices just mentioned, the circuit includes one small transistor, one diode, a string of zener diodes, four capacitors and eight resistors. Ql is the MJ10012 power Darlington transistor. It is the workhorse of the circuit, switching the heavy currents through the coil. Since it is a Darlington transistor (essentially two transistors connected in cascade) it has high current gain and so requires only a small base current to switch the heavy current in the ignition coil. Ql also has a high voltage rating sufficient to allow it to withstand the high voltages developed across the primary winding of the ignition coil. To be specific, the MJ10012 has a collector current rating of 15 amps How Kettering Ignition Works +12V FROM IGNITION SWITCH The conventional ignition system fitted to all cars is based on a system developed by Charles Kettering in about 1910. It is only in the last decade or so that significant refinements have been made to Kettering's circuit to improve its reliability and performance. The standard Kettering circuit is shown in Fig.2. This shows a battery connected to the primary winding of the ignition coil and with the current interrupted by the distributor points. The distributor points are opened and closed by a cam on the shaft of the distributor. The distributor cam is arranged so that the points are opened at the start of the firing stroke for each cylinder. When the distributor points close, current builds up in the primary of the ignition coil and produces a magnetic field in the iron core. This magnetic flux is the energy stored in the coil. When the points open, the coil current is suddenly stopped and the magnetic field collapses. This produces a sharp voltage spike across the coil primary winding. Now, let's imagine that the points capacitor has not been included in the circuit. As with any inductance, the voltage produced across the coil primary is such that it attempts to maintain the current through the points. If you consider that one side of the coil is tied to the + 1 2V terminal of the battery, the other side of the coil swings negative by hundreds of volts. The natural consequence of this large voltage at the points terminal of the coil is that an arc develops across the points as they open . The arc tends to maintain the coil current at its previous value until the points have opened too wide for the arc to continue . Having an arc across the points each time they open is bad news because it means that the point contacts get seriously burnt and pitted. The cure for this is the capacitor connected across the points. At the instant the points open, the capacitor appears as a short circuit (because there is no voltage across it) and so the voltage across it now begins to rise at a rate determined by the inductance and resistance of the coil. And, the lack of any voltage across the points as they open means that no arc occurs. Meanwhile, the ignition coil is also a transformer, so the large voltage spike which appears across the coil primary is stepped to appear across the secondary. The secondary coil voltage is then fed via the rotating contact in the distributor and via the high tension leads to the appropriate spark plug. It is the voltage required to fire the spark plug which ultimately determines how much voltage appears across the coil. This can range from under 5000 volts to over 15,000 volts, depending on the conditions within the cylinder. In the lc1te 1 950s a change was made to the Kettering ignition system with the addition of the ballast resistor. This resistor was placed in series with the coil primary so that, effectively, the peak and a collector voltage rating Vceo (the rating with the base open circuit) of 400 volts. Its current gain at a collector current of 6 amps is typically 350 but can range as high as 2000. In fact though, the current gain of the transistor is not really all that important in this circuit since we drive the transistor's base pretty hard to make sure it is well and truly saturated (ie, turned hard on). IGNITION COIL PRIMARY 10 I 10 ~ TO CENTRE POST OF DISTRIBUTOR SECONDARY ...J FIG.2 voltage applied to the coil was never more than about seven volts. When the engine was cranked over, and battery voltage would normally be low, the ballast was switched out to apply the full battery voltage to the coil. This gave a hotter spark for starting but meant the points were more liable to be severely burnt because of the heavier coil current. Pros and cons of Kettering ignition The advantages of the Kettering system are that it is simple, gives plenty of spark energy at low engine speeds, and is easily adjusted and maintained by the average motorist or mechanic. The disadvantages are that spark energy is greatly reduced as engine revs rise and that the points quickly burn out and need frequent cleaning, adjustment and replacement. This means that the engine is rarely in peak tune. The above explanation of the Kettering system should be regarded as a brief summary of its operation because the more you look into its operation, the more complex it becomes. For example, the ignition coil is connected as an autotransformer and the two windings are connected so that the spark plug voltage is negative with respect to the chassis. If the connections to the coil are reversed, the spark plug voltage is reversed in polarity and this makes the spark plug much harder to fire. The required voltage to fire the plug can be 20% to 40% higher than for the correct connection. The reason for this is that the centre electrode of the spark plug is hot and is therefore an electron emitter. This makes it much easier to fire with a negative potential applied. When Ql is turned on (to feed current through the primary of the ignition coil), its base current is supplied via a 1000 5 watt wirewound resistor. Ql is turned off when ICl pulls its output pin 7 to MAY 1988 35 COIL CURRENT (a) I~ ►/]~► M /1_______...,____/1--t--------TIME n M(ms) 5 10 15 20 25 30 COIL CURRENT (ms) (b) TIME 0 10 15 20 25 30 Fig.3: this diagram shows the primary coil current with and without dwell extension. In (b), the spark duration is fixed at one millisecond and so coil energy is not wasted in useless primary resonance. This allows the the coil current to start from a high value for each cycle rather than from zero. ground, which effectively shunts the base current for Ql to the zero volt rail. Ql has an adequate collector voltage rating to cope with the high voltages developed across the primary winding of the ignition for all normal spark plug conditions. But if a spark plug lead becomes detached, the coil primary voltages can go to extreme levels and thus cause "punch through" of the Darlington transistor. Protection against that circumstance is provided by the string of four 75V 1W zener diodes. These limit the maximum voltage at the collector of Q4 to 300 volts. Wetting current Shown on the lefthand side of the circuit are the points in the distributor, together with the points capacitor which is left in place. When the points close, current passes through them via the 470 5W resistor. Depending on the battery voltage [between 12 and 14.4 volts under normal conditions), the points current is around 250 to 300 milliamps. This relatively high current is necessary to keep the points clean and stop them becoming fouled in the fume-laden atmosphere inside the distributor cap. When the points open, Q2 is turned on by base current supplied via The high-power Darlington transistor is installed on the outside of the diecast case and fitted with a plastic cover to prevent shorts or "tingles" from inadvertent contact. 36 SILICON CHIP the 470 resistor and diode D2. Capacitor C2 is there to filter out hash and to provide a degree of "de-bouncing" for the points. When Q2 turns on, its collector is pulled low and the resulting negative-going signal is fed to a differentiating network consisting of capacitor Cl and the 470k0 resistor. The O.lµF capacitor at pin 3 of ICl· filters the internal reference supply for the comparator input at pin 5. Pin 5 is normally held high via the 22k0 resistor and 470k0 resistor to pin 6. The 22k0 resistor provides current protection for the zener clamped input. The pin 5 input is used to provide the timing signal for switching Ql. As soon as Q2 switches on (taking its collector low) pin 5 of ICl is pulled low via capacitor Cl. ICl then pulls its output at pin 7 low and this turns off transistor Q2. The interruption of the coil current then causes a high voltage to be developed to fire the relevant spark plug. Capacitor Cl now begins to charge via the 470k0 resistor and after about one millisecond, the voltage at pin 5 reaches the threshold of a comparator inside ICl. This causes the output at pin 7 to go high so that Ql turns on again. Thus the spark duration is limited to one millisecond. When the points finally close again, Q2 switches off and a positive signal is applied to pin 5 due to the charged Cl. This has no affect on the operation of ICl and the voltage is clamped with a zener diode at pin 5. Cl discharges via the 2.2k0 and 470k0 resistors. Because the spark duration is limited by ICl, the total energy stored in the coil is not fully dissipated each time a spark plug fires. Paradoxically, this means that the spark energy is actually higher. This apparent contradiction is explained by Fig.3. Fig.3(a) shows a plot of ignition coil current when the time between sparks is 10 milliseconds. This corresponds to a spark rate of 100 sparks/second or 3000 RPM in a 4-cylinder motor. Note that no current flows for about 50% of the time, because this is the time the points are open. plugs themsevles. So there is more likelihood of a high tension failure. Second, if the system fails (unlikely but possible) you will need to change all the plugs back to their normal settings in order for the car to start and run easily. Third, if you open up the spark plug gaps, the resulting spark may have a longer path, but because it requires a lot more energy to maintain that spark, it will extinguish earlier. So you will not get the full advantage of the dwell extension. Construction Fig.4: the wiring diagram. All wiring from the board should be run in 4mm auto cable which has a generous current rating. This means that for about 50% of the time the ignition coil is doing nothing at all, even though the actual spark lasts for less than a millisecoqd. And after this millisecond, any coil energy which was not dissipated in the spark is then wasted in a useless ringing of the primary coil winding (it resonates with the points capacitor). Now have a look at the waveform of Fig.3(b). This is with dwell extension, where the Darlington transistor Q1, handling the coil current, is switched on one millisecond after having been switched off. Now, instead of the coil current starting from zero amps after each spark, it starts at a level of several amps and gets close to the saturation current before the next spark is required. So each time the Darlington transistor is turned off, the coil is able to deliver much higher energy to the spark discharge. Effectively, the dwell extension circuit means that the current through the coil is much higher at all times. More current means a lot more spark energy. And more spark energy means a longer spark duration. That results in better fuel combustion. There is one drawback to putting more current through the coil the coil gets somewhat hotter. But in practice this has not been found to be a problem. Spark plug gaps In the past it has been common practice by car enthusiasts, when they have fitted electronic ignition, to increase the spark plug gaps. This was done to take advantage of the higher spark voltage and thereby obtain a longer spark "path". We don't recommend this practice, for a number of reasons. First, it places much greater voltage stress on the car's high tension components; the coil, distributor, spark plug leads and the spark 0 0 CASE ~-INSULATING BUSH ~-soLOER LUG <at>-WASHER ®----SPRING WASHER <at>----NUT Fig,5: the Darlington power transistor is mounted using insulating bushes and a mica washer. Don't forget to use heatsink compound. The circuitry for our high energy ignition system is housed in a small diecast box. It may not look "high energy" but it is. The box measures 110 x 30 x 63mm and provides what little heatsinking the main Darlington transistor needs. Under normal operation, the transistor and the case become warm but not hot; or no hotter than the surrounding metalwork underneath the bonnet. All the circuit components, with the exception of the MJ10012 transistor, are mounted on a printed circuit board measuring 102 x 59mm (code SC5-1-588). Note that the diecast box is the only type that we recommend. This is because it is splashproof, rugged and provides the heatsinking for transistor Q1. We don't recommend folded metal cases because they are not splashproof. Begin construction by mounting components onto the PCB by following the overlay diagram. Note that because the PCB is designed to be compatible with Hall Effect distributors, some component holes are shown vacant. These holes should be ignored. Mount the two 5W resistors so that they are raised about 1mm from the PCB surface to allow cooling. The five diodes should be mounted with a loop in one of the leads to provide stress relief. For the remaining components it is important to insert them into the PCB without stressing their leads. The component leads should move freely in the PCB holes before they are soldered. Once assembly of the PCB is complete, work can begin on the diecast box. Drill holes for the corner mounting positions of the PCB, a MAY 1988 37 Background to Electronic Ignition Conventional ignition systems suffer from two basic drawbacks. First, the points deteriorate quickly and have to be frequently cleaned, re-gapped and the timing adjusted in order to keep the engine in reasonable "tune" . And once they have been freshly set they immediately start to deteriorate again. So much so that most car manufacturers recommend cleaning and adjustment of the points at least every 15,000km or so. Ideally though, points need to be adjusted much more frequently, at intervals of 8000km or less. Second, the spark energy available from conventional ignition systems falls off with increasing engine speed; ie, the more sparks required, the less energy per spark. This is because it takes an appreciable time for the coil primary current to build up to its full value. As engine revs go up, there is less time available for the current to build. With a typical ignition the time taken for the coil current to reach its maximum value (and thus give maximum spark energy) is around 15 milliseconds or so. And with a typical engine, the points give a duty cycle of about 50%. This means that if the sparks are required less than 30 milliseconds apart, spark energy will be reduced from the maximum level. Just to put that in perspective, if the sparks are only 30 milliseconds apart, that corresponds to a spark rate of only 33 cord entry in the side of the box large enough for the grommet, and finally holes for the earth terminal, transistor mountings and the base and emitter leads. The transistor is mounted on one side of the case with the emitter lead located near the relevant connection on the PCB. The transistor is mounted using a mica washer and insulating bushes to electrically isolate it from the diecast case. The method of assembly is shown in Fig.5. You can mark the holes for mounting the transistor using the T0-3 mica washer as a template. After 38 SILICON CHIP sparks/second which is equivalent to only 990 RPM for a 4-cylinder engine, or not much more than typical idle speed. Incidentally, if you talk about "duty cycle" of points to automotive electricians they are likely to look at you as though you come from another planet. Car manufacturers specify duty cycle in terms of "dwell angle". For example, for a 4•cylinder motor, the distributor cam has four lobes and therefore, for a duty cycle of 50% (ie, points closed for 50% of the time), the dwell is 45 ° or a little more. Typically, for a 6-cylinder motor, the dwell angle is 30 to 35°. Early transistor ignition To overcome the problem of the long times required for coil current to build up to maximum, early transistor ignition systems used special low resistance coils which pulled a much higher current, sometimes up to ten amps or more . This wasted a lot of electrical power and put a big load on the car's electrical system. (In essence, this idea is back in vogue with the "high energy" ignition systems used in cars such as the Holden Commodore.) In the seventies, enthusiasts fitted capacitor discharge systems which gave very high spark energies but were plagued with two problems: unreliability of the electronics and "cross-fire". Cross-fire was due to the high 7 5mm DIA. _J I LtJ 19mm LtJ I ~32mm~ Fig.6: this eyelet lug assembly fits over the points terminal on the coil (see text for connections). energy and very fast risetime of the voltage applied to the spark plug. Not only was the wanted spark plug fired but there was enough energy left over to give weak sparks in other cylinders. This gave symptoms similar to 'pinging' and, in severe cases, could lead to breakdown of piston crowns. These days, the_use of capacitor discharge systems is confined to motorbikes, outboard motors and motor mowers. With the introduction of the Chrysler "lean burn" engine in the late seventies, another variation on transistor ignition was introduced: dwell extension . This makes use of the fact that in a transistor system, there is no reason why the switching transistor should not turn on again once the spark has been extinquished . In a conventional system, once the spark is extinquished, the remainder of the enrgy stored in the coil is dissipated in useless "ringing" in the primary winding. By turning on the switching transistor before the spark actually extinquished, primary coil resonance never occurred and so the average energy stored in the coil was much higher. Thus the energy per spark was maintained to much higher engine revs. This may seem like a paradox but is demonstrated in the waveforms shown in Fig .3. The ignition system featured in this article relies on dwell extension to give high spark energy. drilling, remove any burrs using a larger diameter drill. With the heatsink area (ie, where the transistor mounts onto the case) free of any metal swarf or grit, smear a thin layer of heatsink compound onto the transistor mounting base and the mating area on the case, before placing the mica washer in position. When the transistor is screwed down, check that it is completely isolated from the case by using a multimeter (switched to a high "Ohms" range) or a continuity checker. The PCB is mounted on 6mm stan- ble at the + 12V side of the coil ballast resistor. However, some vehicles have the ballast resistor as part of the wiring lead to the coil and this means that the + 12V connection must be made at the fuse box. Fig.7: the full size artwork for the printed circuit board. BALLAST RESISTOR HT +12VTO IGNITION CIRCUIT TO COLLECTOR OF 01 Fig.8: if making a direct connection to the ignition switch is too difficult (in cars with the ballast resistance in the harness), you can use this relay hook-up to make a more convenient connection to + 12V. doffs within the case. We recommend using shakeproof washers on all screws to ensure that they don't become loose. The wires to the power transistor and to the various external connections should be via 4mm auto cable. This won't fit into normal PCB holes so we suggest you use PC stakes. Use one-metre or longer lengths of wire to provide the chassis, points, coil and battery connections to the circuit. Installation Choose a convenient and well ventilated spot in the engine bay, away from the heat of the exhaust manifold and clear of any possible splashing from water. If you can, choose a position reasonably close to the coil so that long wires can be avoided. For our prototype, we were able to mount it simply with two large self-tapping screws in one side of the case and into a bulkhead near the wheel well. It was just a matter of having suitable holes drilled in the case and bulkhead. Then insert the two screws and then screw on the lid of the case. A plastic case fitted over the power transistor is a good idea because it prevents any possibility of shorts from stray tools. It can also avoid the possibility of a "tingle" to any unsuspecting mechanic working on the car while the engine is running - and that could include you! After mounting, the electrical connections can be made. We recommend an eyelet/solder lug assembly for the points connection, as shown in Fig.6. This connects to the standard points side of the coil and the collector of Ql connects to this at the solder lug point. The second (isolated) eyelet connection goes to the points and the solder lug to the points input to the transistor ignition. This method allows a quick conversion back to standard ignition should the transistor ignition fail. The final connection for the transistor ignition is to the + 12V supply which comes via the ignition switch. In some cars this is accessi- Once the ignition system is installed, the vehicle can be tested. The ignition timing can be checked using a timing light in the normal way. Note that if you use a dwell meter, it will give misleading results due to the extended dwell feature of the ignition. The points gap should be set exactly according to the manufacturer's spec. If you haven't replaced the points for a fair while, it is a good idea to install a new set. And while you won't have to replace them for a long time, if ever, it is a good idea to check and adjust the points gap (and re-do the timing) every 20,000km or so, to compensate for wear in the rubbing block. Next month, we will publish details of how to mate versions of this high energy ignition system to Hall Effect distributor heads. tc ....... •,..•❖•·•·· ■ ■ ■ ■ ■ ELECTRONIC SYSTEMS ■ ■ ■ EQUIPMENT RACKS ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ AuS~flAL AN MADE EX STOCK KITS, SUB RACKS, RACK ACCESSORIES, INSTRUMENT CASES, OEM RACK SPECIALS DESIGNED & MADE BY A AUSTRAL A "' PTY. LTD. /03) 729 7255 ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ FTY 2, 7 MICHELLAN CRT., ■ ■ ■ ■ BAYSWATER VIC. 3153 MAY 1988 ■ 39