Spark Ignition tor fails, the engine will often continue to The main use of the continuity light is to Troubleshooting run, with the spark jumping two gaps, one see if the points are working and the timing at the resistor break, and another at the is correct. With the off, clip by Bob Angel plug gap. The engine may run, but it's one lead of the light to the insulated point Let's assume you have an likely to be intermittent, causing severe and the other to engine ground. You can erratic engine run. If you usually get a close idea of the 's top have a mechanically radio interference. An intermittent connection anywhere center position by pulling the prop up on solid spark ignition compression. Note the position of t e prop, engine there are usually can cause radio glitching to the point of h then move the blade backwards and stop just two causes of ragged control loss. Luckily the cutoff switch will usually function well enough to shut down when the light comes on. running-fuel or spark. A trained ear can You've just found where the points will usually identify the stuttering miss of an the engine. break, and you can estimate the prop's intermittent spark. The engine runs almost An ohmmeter is useful in detecting the resistor failure. Make an end to end check angle between points breaking and top dead at full speed with an occasional complete center. Some basic information: the plug cutout. Expect anything from a plug of the high tension wire, while you pull fires when the points break (open), not change to complete dissection of the and wiggle the connections. If you can't when they close. The prop should show a ignition system to find the cause. get access at the coil end, push a pin into the wire and connect to that. If your difference of 20 to 45 degrees (spark A weak spark will often imitate a fuel advance) for the engine to be expected to problem by responding temporarily to ohmmeter blew out and your eyeballs lit start. If you're hand starting as you should needle valve tweaking but won't hold a up, you should have turned the system off. with most sparkers, you'll want to retard the steady setting, and it can be hard to tell the Serious contest fliers carry a spare high spark below 45°. difference. So we'll keep an open mind tension lead. Using the test light, I've quickly found when the symptoms appear to be fuel Resistors can also fail internally. It would be rare, but the resistor could drive washer installed in the wrong related. possibly show both continuity and proper position. A Brown Jr. can be The biggest single source of problems is installed in 4 positions, 3 of which are failed solder joints. I've had very few resistance when cold, and open wrong. failures of coils, transistors, or even A Super Cyke, being a more advanced condensers. I recently had my first failure engine can have it's cam installed in only of a microswitch. And NiCd batteries go one wrong position of two possible. You out, but usually just by dying slowly. We'll can also estimate degrees of dwell by make up a first law of ignition systems rotating the prop and noting positions as right here: "A wire never breaks in the the light flashes on and off. middle." And if you're setting the advance on Wiring failures occur at unsupported stiff an engine such as a McCoy, where the sections around solder joints. Vibration is points will be locked down and a the main culprit. If you solder good joints used, the continuity light becomes even and support each one, it will be much Robert Shoebridge, New Zealand. Sch- more essential when you're watching a stronger. That 10K ohm resistor in the high maedig Stick is one of the author's favorites degree wheel while at the same time setting tension line to prevent radio interference because it makes good test bed for different a precise advance to let's say 44°. has been the most consistent failure, so I've engines. Photo by the author at Eldorado Here is a simple test to see if the worked on improving it. Dry Lake, 1997 SAM Champs. airplane's ignition system is the problem. I've gone from or watt resistors to 1 1/4 1/2 Just install a glow plug and see if the or 2 watt because they have larger wires. 1 during a run. Substitution would be about engine runs. If it runs on a glow plug, you install the resistors with at least a 1" the only way to find this problem. The just might be onto something. It may not section of flexible wire between them and higher wattage resistors mentioned above run as fast on glow as ignition, because you the clip. I splint the resistor would be less subject to internal failure. can't control the timing as precisely. with a length of toothpick extending past Continuity light. Here's the first handy We'll describe a clip-on ignition set in a both solder joints, potted and encased in tool for the troubleshooting kit: later installment. It can be used for engine clear shrink tubing. Make up a simple continuity light break-in or for field testing to see if the on- consisting of a C or D cell with a 1.5v Spark plugs suffer from vibration, and board ignition system is at fault. you need to protect them and the resistor. flashlight bulb wired in series and taped to We welcome reader contributions of any Those old Champion plugs will shake their the cell. Solder it all together with a pair of peculiar experiences or tips you'd like to center electrode loose if you use a heavy 10" lead wires with alligator clips. Touch share. RLA alligator clip on them, so use a lightweight the clips to a pair of wire ends and if there's wire clip. continuity, the bulb lights. You could use When the high tension in-line resis- an ohm meter for this, but in field conditions the light is much handier. Spark Ignition Troubleshooting, Part II see if the spark is jumping. suspect point float just pull the moving by Bob Angel If you get a good continuous spark point open and compare its spring pressure e now have fewer when you scratch the file, it shows the to a couple of other engines. Most engines W spark plug prob- rest of the system is probably working have more than enough spring pressure to lems than we did in the and you may have a point problem. prevent float, and excess spring pressure old days, and by using Maybe, but if you can't get a good series just creates drag on the engine. I've put a NiCd cells and transis- of sparks, you now have a stronger clue small prop on a McCoy 60 and run it tor ignition systems, plug life has also that the problem lies outside the points. beyond 15,000 with no float. If your been improved. But plug problems still Jim Adams had an erratic running engine has been running fine and suddenly occur, and one of the easiest things to Brown Jr. which had the modern develops a miss, I'd look elsewhere before check when the engine goes sour is to Hurleman type timer. It turned out that worrying about point float. swap a known good plug into the system. the riveted-on moving point had loosened Batteries have always been a problem. Not necessarily a new plug, but one ever so slightly and was only making NiCds are preferred because ounce for you've previously tested. Even new plugs intermittent contact. Jim soldered the ounce they deliver more amps under load, can have a hidden flaw. point to its spring and then he soldered even though dry cells may show higher Timers (breaker points) have several the other end of the point spring also, no-load voltage. And since dry cells must possible failure modes, some of which because it's just crimped to the timer be replaced often, they are more likely to can be tough to identify. If a timer frame. After Jim's experience, I did the be used in a spring loaded battery box, problem is suspected, first hook up your same thing to my Brown Jr., just for instead of being soldered together. Battery trusty continuity light. insurance. A problem like this might boxes are notorious for failures. Think One clip goes to ground and the other to escape detection with the test light. about how often a flashlight fails for no the insulated point. The lead from the Henry Smith of SAM 21 used a strip of other reason than poor battery airplane's ignition system to the point can copier paper to clean his points. Henry connections. be left attached but keep the system had stuttering problems until he found We've found that 3 cells greatly improve switched off. Turn the prop through and that the copy paper had put a coating on reliability over 2 cells. If you need to save watch for the light to indicate points the points. John Richmond of SAM 26 weight, go to 3 smaller capacity cells. For closing and opening. The bulb should stored his engine with a piece of our use, 270 mAh cells are quite adequate, light during the piston down absorbent paper closed in the points to and can be used in a transistor system indicating point closure and the start of soak out oil. But John missed a flyoff without boosters. If you go any smaller, it dwell, and should go off about 45' or less when a small speck of the paper stuck would be a good idea to use a booster for before top dead center. If the light stays between the points during removal. starting. I once stripped down a 9V on continuously, remove the on-board I was getting ragged runs on a McCoy rechargeable battery, hooked up 3 of its system's wire to the point and try again. 60 and found that the fiber cam follower tiny cells to an ignition system and ran an If the light still stays lit continuously, it had been slightly overlapping the cam drive O&R 23 for about 9 minutes before it indicates a short in the points or points area on the , and was began to miss. not opening. If the light never lights, there running partially on the solid crank edge. Ignition service is more severe on is an open circuit caused by points not Filing a few thousandths from the edge of batteries than radio use, so expect to closing, poor timer to engine ground, etc. the follower fixed it. You often need a replace the cells more often. A year or two A second test is simulating point magnifier and very careful inspection for is about the expected life of a 270 mAh operation to tell you if the rest of your this sort of thing. battery, and smaller ones will go much ignition system is operating. Take a "Point float" has always been a source sooner. You should get over 4 volts with a coarse file and two test leads with of worry, but its actual occurrence is light load on a freshly charged 3 cell NiCd alligator clips on each end. Attach one fairly rare. Point float can occur when the pack, and around 3.6 V or less, you may lead between the file and engine ground. moving point spring is too weak, the begin to get missfire. Be sure the points are open. Attach the RPM is high, and possibly the dwell You can buy neat little 270 mAh, 3 cell second lead to the insulated point, and (closure time) ground into the cam is packs made for telephones. Buy only ones clip some sharp edged metal object such short. The idea is that the cam grind drops with cylindrical cells. I tested the disc as a short piece of piano wire to the lead's away from the cam follower faster than shaped button cells and got very short life. other end. the moving point can follow, so the points Besides, the button cells are unvented and We're going to switch the ignition close late, giving short dwell and weak could crack or even explode if fast system on and rake the piano wire across spark. charged. SR Batteries can make up 3 the file to simulate point operation. But Point float would be a possible cause of packs in almost any capacity, even down first the high tension lead needs to be a rough running engine. If you to 150 mAh. RLA removed from the plug and positioned near engine ground to

Spark Ignition Troubleshooting Part III by Bob Angel tery condition by current flow with points closed (usually 2 to 4 A real help in isolating amps), and what normal readings should be when the engine is ignition problems is a clip-on running (usually 1 amp or less) . ignition system. You can use it Spark plug: Substitution of a known good plug is easy and for bench running or hook it up about the only way to find a bad plug. to an airplane quickly to see if Points: A continuity light or ohmmeter clipped to the points can the on-board ignition system is tell you if points are shorted, open, or operating normally. You can faulty. also estimate dwell, find a cam positioned wrong or estimate The clip-on can be a simple, degrees of advance. Add a degree wheel to the prop shaft, and you wired-together set of coil, bat- can find exact dwell or advance. You can do similar things with the teries, etc.; with three connectors clip-on ignition set by watching the ammeter, but it's not a good for ground, points and spark plug. idea to leave the points closed too long with the spark system hot. Or it can be a more elaborate enclosed unit incorporating an On board ignition system: If the engine runs OK on a glow plug, ammeter. it indicates an ignition system problem, not a fuel feed problem. If In the August 1985 issue of Model Aviation, Bill Schmidt, as a it runs OK on a clip-on ignition set, you know points and plug are guest in D.B. Mathews' column, published a clip-on ignition set OK, and the problem is in wiring or ignition components. If you housed in a Tupperware container. The article has some lack a clip-on set, the coarse file mentioned in Part II (SAM Speaks worthwhile text, photos, and a schematic. It's available through the #144) can be used for breaker point simulation, which can tell you SAM library. The schematic, as published, had one small if the on-board components are producing a reasonable spark. omission, that of the ammeter. The 0-5 amp ammeter is placed in Coil: Make an ohmmeter check through all three coil ter- series in a battery lead. Be sure to ob minals and compare with a serve proper polarity. known, good similar coil. I had built my own version of This should reveal an open in- such a set shortly before Bill's ternal circuit, or shorted windings. was published; Poor timing. Too Melted wax from inside the coil is late to "scoop" Bill and too early a sign that it has been overheated, to take advantage of his advice. but I've seen coils with this But the designs are essentially the symptom which still operated well. A common failure mode is same, other than a few small \ details. Bill used a push-on, push- an intermittent internal connec- off switch which he felt he could tion. slap off faster for emergency shut Condenser: Most transistorized circuits (recommended) no longer down. I prefer my toggle switch to see at a glance whether the use a condenser (capacitor). A few electronic guys have switch is on or off. Bob's clip-on ignition system for troubleshooting on-board components capacitor checkers, but Bill put the battery inside the and wiring. Switch off the internal system first. If the motor runs substitution is about as easy and box, but I left mine outside and properly with the clip-on attached, it's a pretty good sign there s capacitors are cheap. use Sermos connectors, so I can something wrong with the internal system. In the text, Bob explains how Transistor: As with capaci- use different batteries. to diagnose the situation using this device. Bill prefers the switch in the tors, some folks have transistor checkers, but substitution can be points-lead where the current is less. I don't trust a transistor not made and a spare is not expensive. to leak, so I switch mine off at the battery. Microswitch: These can show normal operation using a On the pictured box you'll notice three pairs of Sermos continuity light or meter, but still be erratic from vibration with connectors at the right. The top pair is battery input and the bottom engine running. You can put a jumper across the Microswitch pair goes to points and ground. An auxiliary battery is usually used connections, start the engine, and see if the missing goes away to power the clip-on set, but I can also plug in the plane's ignition Electronic switches such as the "E" switch or "Hot Spot" can battery to power it. That can give you a clue about condition of the have their own peculiar problems which we've dealt with in earlier on-board battery. The static, points-closed ammeter reading will columns. Due to the complexities involved in troubleshooting and drop as battery current drops. frequent returns of good units, Bob Holman (for one) has stopped The middle pair of Sermos connectors are "amps out" leads supplying these. which go through the ammeter (un-switched) so the meter can The hard cases may take lots of wire tugging, close inspection of be used separately from the ignition system. points with a magnifier, or part-by-part substitution. If all else fails, you can always build a twin pusher. Robert L. Angel, 1001 When using the clip-on set, the ammeter needle pops up when the points close, letting you know how they're operating. As you Patterson Rd., Santa Maria CA 93455. gain experience, you'll learn to recognize bat-