When setting up your distributor...
When setting up your distributor before firing the engine the first time, you have to make sure the cylinder you are timing off of is on its compression stroke. It can be easy to confuse it for the induction stroke, but that mistake throws the timing way off. One way to check is to pull the valvecover and check that there is lash on both the intake and exhaust valves. If you are on the induction stroke the intake will either be open or not have any lash.
Ignition problems can be infuriating. They always seem to pop up at the worst time and because they are hard to visually spot they can be difficult to find the source and correct. Adding to the problem is the fact that high compression, high revving racing engines require a strong, hot spark to reliably combust the air/fuel charge and any weaknesses in your ignition system can easily result in a misfire.
There is more to a properly set up ignition system than dropping in the distributor and snapping on the plug wires. This month we'll take a look at special precautions and steps you can take to ensure your distributor and ignition system are performing at peak efficiency.
The first step is to get the distributor properly installed, but first make sure you have the correct distributor gear to go with the camshaft you are using. If you're using a cast camshaft, a cast-iron distributor gear will work well. A brass gear will also do fine. But a cast distributor gear with a steel camshaft—like you will often use in aggressive roller cam applications—will lead to excessive wear. Any time you are running a steel camshaft, it's always a good idea to make sure the distributor is equipped with either a brass gear or the less common composite gear.
Many high end distributors,...
Many high end distributors, such as this unit from MSD, feature a moveable collar which helps you dial in the correct engagement between the distributor gear and the drive gear on the camshaft. This is an extreme example, but a good one nevertheless. Notice how worn the brass distributor gear is on this unit. Although it’s way past time that this gear should be swapped out, it still did its job. The brass gear is designed to sacrifice itself instead of wearing the drive gear on the camshaft. This brass gear can be swapped out quickly and without much cost, meanwhile the drive gear on the much more expensive steel camshaft is still in good shape.
In a properly built race engine, a brass distributor gear should last at least a full season of racing. It may last even longer; just make sure to check it whenever you are rebuilding or refreshing the engine. Although it may not be obvious at first, in a wet sump engine a thicker oil will often cause the gear to wear more quickly than a thinner motor oil. This isn't because of the oil's ability to lubricate the gear as the teeth mesh with the cam gear, but because the thicker oil causes more resistance for the oil pump. Because the end of the distributor shaft engages with the oil pump to power it, this extra resistance can cause extra wear on the gear teeth.
When installing the distributor in the engine, you should also make sure the gear properly engages with the cam gear. There must be a small amount of play between the distributor and cam gears. To test this, once the distributor is in place, with the cap removed, place your hand on the rotor and see if you can move the entire distributor shaft up and down just a bit. If it doesn't move, that means the distributor shaft is likely bottomed out on either the cam gear or the oil pump driveshaft. You can adjust this by using spacers between the distributor collar and the mounting flange on the engine. Some distributors can also be ordered with a moveable collar that's adjustable for height.
Right Way Wiring
MSD ignition systems have been one of the most popular in racing for years because they work well and provide multiple sparks each firing cycle to make sure the air/fuel charge ignites. MSD's ubiquitous 6AL ignition box is practically an icon among circle track racers, but there is a common problem among racers that attempt to modify the system.
With a stock MSD ignition system using a 6AL box, the plugs connecting the distributor to the ignition box can't be plugged in backwards. Many racers, however, replace the standard plug between the distributor and the 6AL box with a waterproof Weather Pack-style plug which is more protective from both water and track dirt. Unfortunately, the wiring is easily confused and it's actually quite easy to get them reversed when re-wiring to the Weather Pack connectors.