The crank-trigger system is...
The crank-trigger system is deceptively simple-just a timing wheel with four magnets epoxied into place, a sensor, and a mounting bracket.
Imagine for a minute that, as a dirt racer, you have the ability to dial down your engine's power output as the track loses traction. Sounds a lot like traction control, right? Well, sort of. You can do this by running a dual ignition system on your engine, but that's not the only advantage.
There's a reason most modern engines use a crank-trigger ignition. Timing the spark off the crankshaft location is one of the most precise methods available. The more traditional method of timing the spark off of the camshaft adds many more opportunities for timing errors. Consider the mechanical steps required before a spark can fire the incoming air/fuel charge: The crankshaft is used to turn the camshaft via means of a timing chain, which can stretch over time. The cam, which is spun by the timing chain on one end and spins the timing gear on the other, is subject to deflection when used in high-rpm applications in conjunction with strong valve springs. That scenario is more common in stock car racing than anywhere else. Timing can also be adversely affected if the camshaft isn't degreed properly. The cam spins the distributor shaft through a set of meshing gears, which wear over time. Finally, the rotor inside the distributor is subject to spark scatter at higher rpm levels.
The conventional distributor...
The conventional distributor is still necessary because it routes the spark from the coil to the correct cylinder.
Steady Spark Timing the ignition spark with a crank trigger is relatively easy. Several racing companies make kits, and the systems are typically legal in dirt Late Model and other types of racing. Clements Racing Engines pays the electricity bill by building all types of racing engines, but it does its best work in the no-holds-barred world of dirt Late Model racing. (The Clements organization was named the 2003 Engine Builder of the Year in the Southern All-Starts racing series.) For the past few seasons, Clements Racing Engines has been using crank-triggered ignition timing on its all-aluminum 800hp Late Model monster engines, and the devices have been so helpful that Clements now incorporates them in any engine package where the rules allow.
"There are several reasons why a crank trigger for the spark timing is an advantage," says Glenn Clements, one of the three brothers who run the company. "But the most important for us is how it calms the timing down. It just gets rid of all that monkey motion involved with running your timing off your distributor. It's not a big deal at lower rpm, but when you get into the rpm ranges that we are racing at, you can see the timing jump around by as much as 5 degrees.
Here's an early sign of damage:...
Here's an early sign of damage: The wiring between the ignition box, and either the distributor or ignition sensor, are backwards. As you can see, the material between the top of the piston and the first ring land is cracked and raised up.
"Before we started running the crank triggers, when we walked through the pits before a race, the question we were most often asked was, 'Can you come check my timing?' It wasn't that they didn't know how to use a timing light; they just weren't sure where to set the timing because it moved around. But now, with the crank trigger, the timing marks under a timing light look rock solid. That tells you a lot about how much more stable the spark is with a system that fires off the crank."
The triggering system itself is actually quite simple. Clements prefers a unit sold by Moroso. Others may differ slightly, but most work on the same premise. A timing wheel containing four evenly spaced magnets bolts to the front of the harmonic balancer. Then, a sensor is mounted on a bracket facing the outside edge of the wheel. Every time one of the four magnets passes the sensor, the sensor sends a signal to the ignition box to send out the spark. After amplification in the coil, the spark is sent to the distributor where it is routed to the correct plug. Because the crankshaft spins two full revolutions before all eight cylinders are fired, only four magnets are necessary in the wheel.
This, obviously, means that the distributor is still a necessity. It is no longer used to fire the spark, but it is necessary to route the energy to the correct cylinder to fire the compressed air/fuel charge. Clements says that when using the distributor for spark routing, perfect phasing isn't necessary.
Within three to five laps...
Within three to five laps at racing speed, this is what happens. As you can imagine, the chunks of metal blasted off this piston have done plenty of damage throughout the engine.
Setting the timing with a crank trigger is much the same as before. You use a timing light to check the timing, but instead of turning the distributor to adjust the timing, you move the sensor in relation to the wheel. Because the crank is spinning clockwise, moving the sensor higher toward the 12 o'clock position (assuming the sensor is mounted on the left side of the timing wheel) will retard the timing. Conversely, moving the sensor closer to six o'clock will advance the timing.
Managing Wheel Spin Just because a crank trigger assembly is mounted to the front of the engine doesn't mean the distributor can't also be used. Smart racers can actually use the cam-driven distributor as a backup timing device and switch between the two as a kind of poor man's traction control. For this setup, Clements recommends setting up the crank trigger at the optimum timing and retarding the distributor timing approximately 4 degrees from that mark.
The sensor is mounted approximately...
The sensor is mounted approximately 11/48 inch from the outside of the timing wheel. It picks up the magnetic field from the four magnets as they swing by and sends a signal to the ignition box to fire the spark. Because the crank spins at twice the speed of the crank, only four magnets are necessary.
Wire the ignition systems to a switch within the driver's reach, and then to the ignition box. If you are using a backup ignition box, use two switches-one to select the timing system, followed by a second to determine which ignition box will be hot. After the ignition box, the rest is typical: A coil boosts the power, and the rotor routes the spark to the correct plug.
The result is that the crank trigger is the primary timing mechanism set for peak power. If racing on a dirt track, the driver has the option of switching over to the distributor timing, if the surface loses traction and wheelspin becomes a problem. Retarding the timing 4 degrees typically cuts the engine's power approximately 5 percent. It's not too much to make the car uncompetitive, but enough to help the driver control wheelspin when exiting the turns. Plus, because the distributor timing is used when peak power isn't the goal, a little timing flutter isn't a big deal.
Wire It Right
Although the crank trigger timing system is dead simple, Glenn Clements cautions that one of the most common-and most costly-errors he sees is bad wiring on the electrical system. This is true no matter which ignition system is used. Many racers cut off the stock connectors on their MSD systems and install weatherpack connectors in order to prevent water intrusion when washing the race car. The only problem with this is MSD wiring can be a little confusing. When using the original equipment connectors, it's impossible to plug in the wires backwards, but when the wires are cut and respliced into the weatherpacks, it's very easy to get things confused. In MSD systems, the violet-and-black wire connects to the green wire-not the violet wire, as you might expect.
As with conventional systems,...
As with conventional systems, timing is read with a timing light shining on the marks on the harmonic damper.
Adding the extra component of the crank-trigger ignition only adds more wires to the equation. If the wires are reversed, the ignition can fire as much as 60 degrees before top dead center (BTDC), which means severe detonation. Clements says they can even adjust the timing so that everything looks right according to the timing light, but the spark will still be dangerously advanced. Once the car is on the track, it can take as little as three hot laps to turn the thing into scrap metal. Almost every time, the first area damaged is the side of the top of the piston where the intake valve pocket is closest to the ring land (because the spark is firing while the valve is still open). After this area cracks and breaks, things quickly go downhill, and the parts bill starts adding up fast.
Fortunately, it's a simple matter to make sure this doesn't happen to you. When using a dual timing setup, Clements has an easy procedure list to make sure everything is in working order. First, double-check the wiring. On MSD systems, the violet wire coming out of the ignition box connects to the orange wire. Connect the green wire coming out of the ignition box to the black wire coming out of the trigger sensor.
Timing is adjusted by moving...
Timing is adjusted by moving the bracket holding the sensor up or down. Moving the sensor closer to the 12 o'clock position on the timing wheel retards timing. Moving it closer to 6 o'clock advances it.
Next, crank the engine and check the ignition timing. Start by setting the distributor timing. This is important so that you will already have the advance set before setting the crank trigger. If you plan to run the distributor timing retarded as a means of cutting engine power, set it at that mark. Now switch to the crank trigger and set it.
Also, when cranking the engine, it can be easier to get it running with less timing, so it's a good idea to crank it with the ignition trigger. Once the engine is warmed up, switch to the crank trigger and get ready to race.
Because the timing wheel moves the crank pulley out, it is necessary to use spacers between the engine and the water pump in order to move that pulley out, also.
When the track gets slick and wheelspin becomes a problem, a secondary timing system that is retarded approximately 4 degrees can make the car easier to keep hooked up.
As you can see on this Limited Late Model motor, even with the crank trigger and distributor in place, the entire package isn't any larger or heavier than a standard ignition timing system.
Here's the rest of the electrical setup tucked away in front of the dash on a Late Model Dirt car. The driver has switches in the cockpit to choose between the crank trigger and the distributor as a timing device, and between main and backup ignition boxes and coils.