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Remembering Ignition Distributors

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My favorite billboard sign of all time was one that once stood over Woodward Avenue during the Woodward Dream Cruise. It had a picture of a 1970 Chevelle and a caption that said, “The only carbs we cared about were under the hood.”

It harkened to a different time – a time of automotive passion that saw high horsepower out of low technology. It was the time of high compression and high octane. It also was the time of the distributor. Maybe that’s why I love them. They were simple, basic, maybe even crude by today’s standards – but they worked. And the ability to tune a car – to really make it run well – was left only to those who took the time to understand them.

It’s been many years since distributors have been used on new vehicles, but that doesn’t mean there aren’t hundreds of thousands still on the road – and there are. Selling distributor components, from small parts to complete units, can mean big profit, and the key to it is understanding the distributor or, more importantly, helping your customer understand them.

As a counter professional, your job – like that of a technician – often comes down to education. You are the teacher, and that’s what your customers expect. It’s very likely, at some point, that a customer will ask you if a distributor is better than modern ignition systems or even try to argue that they were.

The answer, of course, is no. (I said I love them, not that they were better.) If you have to explain it, in a nutshell, there are too many wearing parts; too many opportunities for higher-than-normal resistance; continuous maintenance; and lack of precision spark control. Many people consider old technology better due to its simplicity, and it would be fair to agree on that point, but functionally it doesn’t hold a candle to anything new.

The Basics

So, let’s take a brief look at distributor technology. The first point-style ignition distributor was developed around 1910 to improve on the difficulties experienced with magneto-type ignition systems for automotive use. This point-style ignition was such a success that it was ultimately used in production cars until the mid-1970s.

The primary service components were the points, condenser, cap and rotor, and the ignition coil was separate from the distributor. The distributor was driven by a gear on the camshaft or, in some cases, an intermediate shaft. When rotating, the ignition points opened and closed off a cam located on the distributor shaft.

How did it all work together? It starts with understanding how an ignition coil works. The ignition coil has primary and secondary windings. When current flows through the primary winding, a magnetic field is created that surrounds the secondary windings. When the current flow is interrupted, the magnetic field collapses and induces high voltage in the secondary windings. The voltage and current from the secondary windings are directed to the spark plugs through the plug wires, distributor cap and rotor.

Inside the distributor, the points are the switch that controls the flow of current through the primary windings of the coil. When the points are closed, the current flows and the coil becomes saturated. When they open, current flow ceases, the magnetic field collapses and high voltage travels to ground through the spark plugs. The reason that the secondary voltage is boosted to such a high level is that the primary winding of a coil contains approximately 200 turns of wire. The secondary windings may contain 20,000 or 30,000. This is why 12 volts supplied to a coil can be transformed into voltages of 20,000, to as high as 50,000.

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By understanding these fundamentals and the fact that ignition coils can differ in the number of windings and ultimately their output, you can see how the amount of and how long the current that flows through the primary side of the coil will affect coil output. Since the amount of time that the points are closed controls how long the current flows through the coil, the critical nature of point adjustment (dwell) becomes apparent.

Now that we know where the spark comes from and how it gets to the plugs, there’s one component left to explain: the condenser. As the points open, current will attempt to continue to flow across them by arcing. The condenser quickly absorbs and dissipates this electrical energy and does the following two things: It eliminates arcing between the points, which would burn them up quickly; and it also puts an abrupt stop to the current flow through the coil, making the magnetic field collapse quickly for more accurate spark control.

Electronic Ignition

So, what is electronic ignition? After all, the points and condenser work off basic electronic principles, right? When electronic ignition first came out in the early 1970s, it (sometimes called transistorized ignition) was still a distributor with a cap, rotor and plug wires and, in many cases, a separate coil. It actually didn’t look different at all until GM released its High Energy Ignition (HEI) distributor, which housed the coil in the distributor cap and was visually much different.

What was different was the points and condenser were gone! No more regular adjustments or regular maintenance; the points were replaced by electronic pickups made with solid-state components. The most common was a Hall-effect unit, which passed a rotating magnetic field in front of a Hall-effect pickup that would detect the magnetic field. Solid state meant the electronic components themselves had no moving parts; their operation is based on fundamental electronic theory.

Electronic-ignition distributors were much superior to their point-and-condenser counterparts. One of the biggest drawbacks to points was that the rubbing block that contacted the cam on the distributor shaft wears constantly during use. Even though a set of points may ultimately last 10,000 miles, for example, since the rubbing block continuously wears, the dwell continuously changes, which causes the timing to change and the output of the coil as well.

It’s easy to think, “If the rubbing block wears, the points will be closed longer. Won’t this allow more time for the coil to saturate, resulting in a higher voltage output?” This is not the case. The correct dwell setting ensures that the coil will be completely saturated. It’s true if the points aren’t closed long enough the coil won’t have enough time to saturate. But if they’re closed too long, that also means they’re not open long enough. If they are not open long enough, the field in the coil will not have sufficient time to collapse and produce the necessary voltage for proper spark before current begins to flow back into the primary side of the coil again.

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So, electronic ignition eliminated the wear and maintenance problems associated with points and condenser, but all electronic ignition distributors were not created equal. Enter GM’s HEI. Another drawback to points was they don’t last long under a constant 12 volts, so voltage through the coil and to the points was limited by either a ballast resistor or a resistance wire, depending on vehicle make. During cranking, the resistance was bypassed so full battery voltage would be supplied to the coil for starting, but then when the key was released to the “Run” position, voltage was limited.

The lower voltage limited coil output and even after switching over to electronic ignition, some systems retained use of the ballast resistor, limiting ignition-coil output. GM’s HEI utilized full battery voltage all the time, and the result was an ignition system with a much higher output.

Another aspect of ignition is that the higher the rpm, the greater the spark requirement. As engine rpm increases on a point-style ignition – even with the dwell set properly – the amount of actual time the points remain closed is less, resulting in a less time for the coil to saturate and less spark when the engine needs it the most.

GM’s HEI was designed so that the dwell increases as engine rpm increases, providing high rpm performance as well as high output and dependability – whereas some systems retained fixed dwell. If you’ve been around old cars, you’re probably familiar with all of the different variations and names of electronic ignition systems throughout the ‘70s and ‘80s. The only one that stayed the same was GM’s HEI. Everyone else followed their lead.

Timing Advance

Before we get into selling components, which will be a walk in the park for you now, we’ll touch quickly on distributor advance. Two types of timing advance can be found in distributors: vacuum and mechanical. Sometimes they have only one type, sometimes both. Timing advance is required because once ignited, the air/fuel mixture in a cylinder does not burn instantly. It takes a certain amount of time to burn. The higher the engine rpm, the earlier the mixture must be ignited to reach the full burn, or maximum pressure at the precise time to force the piston down.

This gets deep into engine theory and design, but the fact is that having the correct amount of advance at precisely the correct time has a monumental effect on engine performance. Mechanical advance uses weights that move outward from centrifugal force. As they move outward, they rotate the base plate of the distributor that supports either the points or electronic trigger mechanism. The higher the rpm, the more mechanical advance is applied until its mechanical limit is reached. Mechanical advance can be “tuned” using different weights or springs.

Vacuum advance also rotates the same base plate of a distributor, but in response to engine-ported vacuum. The more vacuum applied, the greater the advance. This is utilized for low-rpm advance before the mechanical advance spins fast enough to come into play.

Selling Distributor Components

What can you capitalize on when selling distributor components? Cap, rotor, plugs and plug wires might be the easier topics, and they’re what a lot of people just ask for. The cap, rotor and wire condition generally can be determined through visual inspection, but if it’s time for a tuneup, a vehicle has a misfire or the customer can’t remember when they were done last, the door is open and it’s a perfect time to sell.

Never guarantee that a cap, rotor and wires will solve a misfire or running problem. But, they can degrade from use and age, and they’re true maintenance items, so don’t forget to point that out.

Spark plugs are a maintenance item that you almost can’t do too often. Some late-model vehicles that still have distributors have efficient fuel-injection systems and engine controls, and the plugs will last for a long time. It doesn’t make sense to unnecessarily replace a good expensive set of plugs on a fuel-injected vehicle, but I shy away from the really high replacement intervals like 100,000 miles. If someone hits 90,000 and says, “It doesn’t call for them until 100,000,” it’s time for plugs in my opinion (they’re getting worn regardless).

For older vehicles with less efficient fuel and ignition systems, the plugs need to be replaced more often. OE-style plugs are the best to recommend with any system, and if it’s a classic that isn’t driven as much, don’t be afraid to recommend a fresh set.

Most vehicle owners will know if they have points and condenser. When old cars were driven daily, points and condenser were replaced at least once a year, just because of mileage. It’s not necessary to do this now, since most cars with these systems don’t see a whole lot of miles. But, like before, if someone opens the door and can’t remember when they were done last, sell them the parts.

It’s always a good idea to clean up the points and adjust dwell, however. If you stock any basic tools, a nice upsell is a point file, a dwell meter, a spark plug gauge and a timing light. This will cover the standard maintenance requirements of a point-type ignition and if they have electronic ignition, just the spark plug gauge and timing light will do.

When someone is doing an ignition tuneup, be sure to ask them about the condition of their distributor-advance components. Vacuum-advance diaphragms go bad from time to time, so they should be checked and replaced, if necessary. Mechanical weights should be taken off and their pivot points cleaned and lubricated. In many cases, the mechanical-advance weights pivot on bushings that commonly wear out, and the weights themselves can have grooves worn in them if they haven’t been lubricated on a regular basis. It’s all a great opportunity for an upsell.

Additional distributor components include seals and bushings and also the electrical connectors that plug into them (pigtails). If someone is removing their distributor for service, a new seal makes sense, but bushings are a harder sell since most people will generally buy a new distributor if the bushings are worn. But, the sale could be yours if you’re the one who helps them understand their distributor. Worn bushings are common on higher-mileage distributors and easy to spot on an oscilloscope, but since nobody really has one of those sitting around in their garage, they’re easy to check by grabbing the distributor shaft and attempting to rock it back and forth.

Any noticeable play means the bushings are worn. Since the trigger wheel or points are driven directly off of the distributor shaft, just imagine what will happen to dwell and timing if this shaft is rocking back and forth in worn bushings.

Dielectric Grease

Dielectric grease is another great upsell. Forget about the silly little packets that give you just enough to get your finger or an application brush greasy – sell them a tube. No, you don’t need to, nor should you use an excessive amount of it, but it’s frustrating to deal with such a small amount. Plus, you can remind your customer of all the additional electronic uses for dielectric grease (don’t let the name throw you off).

Dielectric grease does not conduct electricity at all. What it does do is seal electric components from moisture, which is why you can find it in a lot of electrical connectors and in bulb sockets. This was the original intention of it: to prevent moisture and corrosion from occurring. An added benefit is that when used on plug-wire boots, it keeps moisture out but also keeps the boot from sticking onto a spark plug or distributor cap, making removal much easier.

An oddball – but one you will run across – is heat-transfer compound. You also may hear this referred to as thermal grease, thermal compound or even heat-sink compound. Have you ever removed an ignition module or other electronic module from either inside a distributor or another location and found that it had grease underneath? This is a compound that is specially formulated so that it transfers heat from the module to the mounting location. It is a true heat sink and very important. Modules that originally were installed with this will overheat if the proper compound is not reused.

A Few More Add-Ons

Just a few final things can finish off the perfect ignition-tuneup shopping cart. When someone is working on a vehicle that is from the early ‘70s, don’t forget to see if their car has a ballast resistor. (You’ll get used to these applications pretty quickly.) They commonly go bad and cause a no-start. It’s never bad to have an extra one in your glovebox.

For the old point-style distributors, there is a specific grease for the distributor cam to lubricate the ignition-point rubbing block. Some points may come with a small packet. If not, be sure to recommend it. Anti-seize also is a good upsell, but it’s not necessary all the time. Make sure you recommend the proper use.

If the plugs are located in a deep well – like a lot of double overhead-cam engines – advise your customer to check for the presence of oil. They may need a valve-cover gasket. And, last but not least, a light lubricating or penetrating oil is nice to have on hand. Many distributors have metal clips that hold the cap in place. These clips commonly get rusty where they attach to the distributor, and it’s nice to work some lubricant in and free them up. It makes it much easier to reinstall the cap.

This might be a lot, but when you have the knowledge, your customer will keep coming back.

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