Is your ignition working? - Old Bike Australasia

On The Dyno: Presented by OEM.DIGITAL Pty Ltd

Mike Garrard is an automotive engine management semiconductor engineer with over 20 automotive engine patents, 12 of which relate to motorcycle ignitions. Mike is the co-founder of OEM.Digital who make the Hand Held Dyno® Ignition. Here Mike explains what everyone needs to understand about motorcycle ignition systems.

First, a quick history of contact points. First designed in 1911 by Cadillac to automate the ignition advance lever mounted on the steering column of a car, the venerable contact points found their way onto just about every engine made up until the early 1980s when they were superseded by more accurate maintenance-free better performing solutions.

Their construction is one fixed side and the other on a leaf-spring that tracks a cam lobes via a nylon follower. They require maintenance because springs weaken over temperature and time and the leaf-spring gets to the point where it can’t follow the cam to the closed position. Instead, the contacts make them bounce off each other. The result is that they are not closed for long enough to allow the coil to build up enough energy for a full-energy spark. Thus the weaker spark is not able to cause a complete combustion and power is lost.

This fact was demonstrated on a back-to-back ignition shootout between a stock ignition and the Australian-made and developed Hand Held Dyno® Ignition. The dyno test was independently performed by Dudley’s Performance in Wyong, NSW. The bike, a stock Z1 Kawasaki, (a model that normally produces more than 60hp), was ridden to the shop with no apparent issues by its owner. But issues it did have! As the dyno run displays, the bike was down a massive 20hp. The cause of this deficit is described in the Dyno charts which I will explain to you.

A word on reading dyno plots. There are two traces: one is torque in ft-lbs on the right vertical axis, and the second is horsepower in hp on the left axis. People will tell you that torque is acceleration and power is top speed, but that’s not actually true, because torque x rpm = power. So, you might correctly claim that low-down torque gives you acceleration out of a corner, but it would be equally correct to say that low-down power (torque x rpm) produced that. The reason both are plotted is that low-rpm differences show up in torque and high-rpm differences show up in power.

What we see in the chart below is the stock ignition’s very unstable baseline run (black line) in torque. The dyno operator Dudley Lister reasonably speculated this was the result of a worn drive chain. Then there’s also a power collapse above 140km/h, another anomaly. As this was a back-to-back shootout nothing was changed on the engine except to swap the stock ignition for the Hand Held Dyno® kit.

On the Hand Held Dyno® plot (Red)we see the previously unstable torque become steady, (ruling out the drive chain) and the power collapse also disappears, informing us that the stock ignition had manifest issues that cost the engine 20hp. The problem with this stock ignition is two fold. The first is what is known as “contact bounce”.

The second problem with contacts is the advance mechanism: two centrifugal weights on a platform with the cam, and two different springs pinning the fixed engine plate to the sliding contact plate. The pegs are spaced the same but the springs are different lengths and expansion forces: this gave the 1960s engine designer two advance curve breakpoints. The first was always idle and pickup because idle is ~ 5°BTDC. The second breakpoint was typically below midrange, 3-4,000 rpm, up to maximum advance ~ 25-35°BTDC depending upon engine achieved by a stop-foot on the cam plate.

If you examine your springs on your classic, you will usually see that the pillars have grooves worn by the springs. Because the radius is so small, just 0.5mm could put your spark curve out by 15°. This isn’t the end of the issues: contacts and cam rotate relative to the distributor shaft fixed to the engine cam, and it wears. Slack between the two causes the cam to shift relative to the engine as it rotates, causing ‘spark scatter’.

In our shootout the Hand Held Dyno® Ignition solved “contact bounce” and “spark scatter” problems because it has an ignition trigger keyed directly into the engine crankshaft making the crank and the ignition as one. There are no wear and tear parts, no springs, worn bearings or pillars, or contact bounce. The cam that triggers contact points and other ignitions is typically just 2cm in diameter; this costs accuracy in ignition timing, and poor accuracy costs performance. By comparison the Hand Held Dyno® trigger is 8cm. This large trigger ring radius provides about 5x the timing accuracy of the contacts cam. This increased accuracy combined with a powerful 32bit processor schedules trigger edges and coil dwell to microsecond (millionth of a second) precision. And recall that in Part 1, OBA 115, the Hand Held Dyno®Automatic Static Timing System needs no timing adjustments, no degree wheel and no timing light. That’s because the datum triggers are in known locations and the ICU calculates when to turn the coil on and when to turn it off to deliver the prescribed advance curve. The stock ignition on the other hand wavers in its timing thanks to the practical variation of cams, contacts and springs: or, for that matter, any advance curve relying on analogue electronics such as most CDI, and many aftermarket contact replacement units.

Solving these issues provided the spectacular benefit measured on the Z1’s engine. But to return to the original question, is your ignition really working well enough? Above is a Ducati 860 baseline dyno run provided by Hand Held Dyno® customer Fred Cousins in Chicago after he did back-to-back tests.

The torque has been scaled to overlay the power: which is not how I do it but illustrates how they are related. The two deep dips (left chart) are the torque curves, and the related smaller dips are flat-spots in the power curves. This is common for a carb bike: I have one on my 1996 Fireblade at 6,000 rpm. Most riders will ride around the flat spot by changing gear. What’s happening is that the resonance of the intake and exhaust system just as the bike comes on cam cause pressure pulses back and forth through the carbs and this upsets the mixture. What’s key here is that the air and fuel vapour in the spark gap when the spark occurs is combustible: between about 10:1 and 22:1 AFR. How does an ignition fix this? Well, the Hand Held Dyno® Long Duration Spark technology keeps the spark plugs lit for longer. This increases the likelihood that a combustible mixture is in the spark gap, and the results can be seen in the ‘after’ dyno plot (above right).

You don’t need a problem like this to get the benefit. During a cold start, the volatile components of petrol evaporate less, and a higher power spark helps. If you’re riding when it’s 10-15°C and you snap the throttle, that gulp of cold air has the same effect: the higher power spark stops the misfire. You decelerate into a corner on closed throttle then want to get back on the power: in-between, your carbs are likely to run lean. Again, the higher power spark will smooth out the response.

As well as much-increased efficiency, it adds up to a more pleasant riding experience. And that’s what motorcycling is all about.