I once knew a twenty-something guy who purchased a 1964 CJ-6 and was unhappy with his Jeep because it didn’t start, run, drive or perform like a modern SUV. The Jeep was hard to start when cold because the young man was from a generation that had grown up with electronically fuel-injected gasoline engines in cars, light trucks and SUVs, so he didn’t understand how a carburetor worked or why it had to be choked.
He also found that the Jeep was “hard to steer” because it didn’t have power steering. It was “hard to stop” because it didn’t have power brakes, and “underpowered and slow” because its four-cylinder engine had only been born with 72 GHP.
In addition to these faults, he thought the transmission/transfer case was worn out “because it made a whiny sound,” and the gears always ground when trying to shift. Plus it leaked oil. And the (vacuum) windshield wipers didn’t work right when the Jeep was accelerating or climbing a hill.
Had he kept the Jeep, instead of selling it to me for less than he’d paid, he would have probably found many other things “wrong” with it and/or to be frustrated about. If he took to a “quick-lube,” he might have been billed for extra grease and gear oil because it had so many lube fittings and gearboxes. This is assuming that the quick-lube people were knowledgeable enough to check not only the transmission, transfer case, and front and rear differentials, but also the front axle steering joints. There may have also been a problem when it came to finding a replacement element for the bypass oil filter, not to mention servicing the oil bath air cleaner.
There probably would have been more frustration if the Jeep had needed a new or rebuilt generator (not an alternator), a voltage regulator, a starter, a water or a fuel pump, because most of these items wouldn’t be found on the shelves of typical auto-mart stores. There may have been additional problems locating basic tune-up items such as a distributor rotor, distributor cap, a condenser and breaker points.
In this case the Jeep was a civilian model. As most experienced military vehicle hobbyists know, most of the above-mentioned items would be twice as hard to find, and probably at least twice as expensive, for the military M170 version of the same Jeep. But, this gentleman hadn’t been looking for a classic vehicle, so one probably shouldn’t blame him for unrealistic expectations or not doing his homework before buying the Jeep.
On the other hand, if somebody is looking for a vintage vehicle, then it is certainly up to him or her to educate themselves well in advance of making a purchase. Aside from scanning the Internet, buying service and operator’s manuals for the vehicle or vehicles you are interested in would be a wise move, and far less expensive than ending up with a vehicle that you don’t want or can’t use.
For those who are new to the hobby
If you are a newcomer to the vintage vehicle hobby, or want to be, you should know that about the only commonly collected vehicles that even come close to performing like modern SUVs are pickups or Chevy Blazer-type vehicles. However, these trucks often lack the rugged military look and battlefield mystique of fully tactical (or “combat”) military vehicles, which this article focuses on. However, the workings of a breaker-point system are similar to those of passenger cars of the same era.
Because everyone is an individual, the military vehicle experience means different things to different people. One can certainly appreciate the time and effort required to fully restore a classic military vehicle to its original factory specifications. But to many folks, the real pleasure of owning an MV comes from getting behind the steering wheel and driving it.
Tune-up before venturing too far
I began my association with military vehicles when I was 16. I bought a Korean War-era M38 Jeep at a city auction. This was back in the day when four-wheeling was virtually unknown to the American public, and Jeeps were so rare — at least in my area — that their drivers usually waved to each other out on the road. This was also a time when most gasoline-powered vehicles had battery ignition systems with distributors that used mechanical breaker points, as opposed to most of today’s cars and trucks that have “breakerless” — and often computer-controlled — electronic ignition systems. In other words, the distributors of most modern vehicles, including most present-day MVs, do not have breaker points. Tuning up such vehicles is a much different process than doing a tune-up on an older vehicle or a vintage MV.
Most WWII U.S. military vehicles had six- or 12-volt ignition systems. Distributors weren’t much different from their civilian counterparts.
However, most common post-WWII (or M-series) U.S. military vehicles have 24-volt waterproof ignition systems. As you may have heard, most of these vehicles, from M38 and M38A1 Jeeps, M151 MUTTs (Military Utility Tactical Trucks), Dodge 3/4-ton M37s, Kaiser M715 1-1⁄4-ton trucks, M211 and M35 2-1⁄2-ton trucks, along with most other tactical U.S. M-series vehicles, will run underwater if fitted with the appropriate accessory equipment. Even without fording kits, the waterproof ignition systems of these vehicles — which basically consist of sealed distributors, waterproof spark plugs and spark plug wires — allow them to be driven through streams or landed through surf on beaches without stalling out, because of water splash. (There are many other features and components that make most M-series vehicles waterproof, such as sealed generators, alternators and starters, as well as sealed fuel systems, waterproof switches, dashboard instruments and wiring; but this article will focus on ignition systems, specifically distributors with mechanical breaker points.)
Thanks to growing up around engines, vehicles and equipment in my dad’s scrap yard, I had a good working knowledge of such distributors. However, the M38 was the first vehicle I had ever seen with a waterproof distributor. It looked a bit daunting — like something not to be messed with. Some people even thought my Jeep had a diesel engine, because waterproof spark wires and spark plugs look a lot like fuel lines and injectors.
Since the Jeep was running well, I left well-enough alone and didn’t tinker with or even investigate the ignition system. I had to learn the hard way why you should be familiar with a vehicle — especially a military vehicle — before taking it on a road trip or out into the bush.
My two best friends and I decided to explore Death Valley in my rugged old “army Jeep.” Again, these were the days when recreational four-wheeling was almost unknown, and most Jeeps were owned by hunters, farmers, miners or ranchers who used their vehicles for work, not play. There weren’t even many MV hobbyists back then!
I’ve written several articles about what to check and how to prepare MVs for long trips based years of sometimes painful experience. But, except for filling the Jeep’s jerry can, and taking five gallons of water and a handful of tools, for my trip I did none of the things I now advise people to do. Nevertheless, and no doubt due to proper previous maintenance at the Oakland Street Department, the Jeep ran fine all day at 45 mph. However, at about 1 o’clock in the morning, climbing into the mountains out of Bakersfield on a winding, two-lane and deserted road, the engine just quit. One moment we were cruising sleepily along, planning to be in Death Valley by dawn and have exciting adventures, and then next we were coasting to a stop in the dark in the middle of nowhere.
Being in such a situation — without proper tools and with only a cigarette lighter for light — is not the time to learn about waterproof distributors! It’s certainly not the time to realize that virtually nothing inside that distributor — the ignition coil, the condenser, resistors, the inner cap, the rotor and the breaker points — are likely to be found at the next gas station, or even the next town!
Figure 1. This is a six-volt non-waterproof system, typical as used on most WWII-vintage military vehicles. A 24-volt, M-series waterproof system differs mainly in the style of components and the ignition coil is usually located within the sealed distributor rather than mounted somewhere else on the engine. Both types of systems, with the exception of late-model M-series vehicles, use mechanical breaker points.
Needless to say, the whole trip could have been ruined because I hadn’t properly prepared for it. Fortunately, and once I managed to get the waterproof outer cap off the distributor, I discovered that the inner components weren’t much different from a civilian model. The breaker points had simply slipped out of adjustment. Using a paper matchbook cover (which is approximately .020 inches thick — a setting at which most breaker point-equipped engines will run), I reset the points and we were on our way again. We did have a cool adventure and returned home without any more problems.
Breaker points: the basics
So, what are breaker points, what do they do, and why do they need to be set, reset and replaced as part of a tune-up, along with other distributor components such as rotors, caps and condensers, and sometimes the ignition coil? Simply said, breaker points make the spark plugs spark by loading and firing the ignition coil, while the distributor, well, distributes, the high-voltage current from the coil (which can be as high as 20,000 volts) to the right spark plugs and at the right time. In essence, breaker points are nothing more than a switch. The only maintenance required is to keep this switch adjusted (how far it opens), keep the contacts clean and replace it when it wears out. However, as with many simple things, breaker points have to be properly maintained.
Figure 2. Except for the additional resistor and coil capacitor, as well as the coil itself being located inside the unit, the setting, maintenance, and replacement of components such as the breaker points, condenser, rotor and inner cap are essentially the same as with a non-waterproof or civilian type distributor.
Figure 3. Two components vital to the operation of a mechanical breaker point distributor are the points themselves and the condenser (also sometimes called a capacitor). The points must set and checked occasionally as to how far they open when the cam lobes come up on the rubbing block. The point contacts must be checked for erosion or burning, and the rubbing block must be checked for wear. Rapid burning or erosion of the point contacts is open caused by a failed condenser or the wrong type of condenser.
A basic mechanical breaker point ignition system is shown in Figure 1. Although it’s a non-waterproof type, as would be found on most WWII-vintage MVs, it’s essentially the same system as used on most common collector M-series military vehicles. However, most M-series waterproof systems have the ignition coil inside the distributor instead of located elsewhere on the engine. An M-series waterproof distributor with its top removed is shown in Figure 2. A close-up view of breaker points, along with a condenser, is shown in Figure 3, while a typical ignition coil is shown in Figure 4.
What makes the spark plugs spark, which ignites the fuel and air mix delivered by the carburetor to the cylinders, which makes the engine run? Most of the magic happens inside the distributor. The distributor has several functions. First, it opens and closes those all-important breaker points that load and fire the ignition coil. Secondly, it does this at the right time so that each high voltage impulse from the coil happens when it should. Third, it distributes these high- voltage impulses to each of the spark plugs through the spark plug wires via the rotor and cap.
Figure 4. An ignition coil transforms a vehicle’s 6-, 12- or 24-volts, into 15- 20,000-volt impulses that fire the spark plugs. A coil operates by creating an electro-magnetic field, and the high voltage impulse is created when this field collapses. “Loading and firing” the coil is performed by the breaker points.
How and why does an ignition coil load and fire? How does it conjure up 20,000 volts when a vehicle only has a six-, 12- or 24-volt electrical system? Should you be worried about messing around with 20,000 volts?
To answer the second question first, while the voltage is high, the amperage is low, and the surge or spark only lasts for a moment. It isn’t like 20,000 volts flowing out of a downed power line. Getting bitten by this spark will make you jump and probably say a four-letter word, but it won’t make you toast. It can make you bang your head against the hood, or fall off a stool if you’re standing on one.
As to the first question, and without going into a lot of detail, an ignition coil is able to produce 20,000 volts from six, 12, or 24 volts by creating a charge with an electromagnetic field between the primary and secondary windings. This charge is built up when the breaker points are closed. When the distributor cam opens the points — when the cam comes around with one of its four, six or eight, lobes (depending upon how many cylinders the engine has), the electromagnetic field within the coil collapses, creating the high-voltage impulse. Again, the breaker points are nothing more than a switch that loads and fires the coil. However, it is an important switch that must be properly set, maintained and replaced when it begins to fail.
Why do the points need to be set? The electromagnetic field within the coil is built up, or loaded, when the points are closed. When the points open, or “break,” the field collapses and the coil is fired. As you may imagine, this process happens very fast when a vehicle is roaring down the highway. If the points are not set correctly and open the correct distance when a distributor cam lobe comes around, the coil may not have enough time to build up a full charge. This results in a weaker spark or no spark at all, and the engine will lose power or misfire.
Breaker points that slip out of adjustment because their mounting screws become loose — as happened on my M38 — may not close, and the coil can’t build up a charge. On the other hand, if the points don’t open, the charge can’t be fired.
Breaker points are opened by the distributor cam lobes pushing against a rubbing block. Naturally, this rubbing block gradually wears away, which means that the breaker point contacts don’t open as far as they did when the block was new. This is why the points need to be checked and/or reset at regular tune-up intervals, which are found in most vehicle manuals.
In addition to the rubbing block wearing away, the breaker point contacts are gradually eroded and/or become burned by the electric current flowing through them. You may have heard someone talking about “dirty points” as being the reason their car or truck wouldn’t start or run right. Breaker point contacts can also become corroded, especially on vehicles like hobbyist MVs that are driven infrequently. Breaker points may also become dirty because there is oil in the distributor, someone put too much lubricant on the cam or used the wrong type of lubricant.
Figure 5. Setting mechanical breaker points is a process that looks and sounds simple. However, the process is often complicated and difficult because distributors may not be easy to reach in many vehicles. Sometimes it may be easier to remove a distributor from a vehicle when installing new points or to reset old ones.
The condenser — sometimes called a capacitor — is another simple, but very important, component in a mechanical breaker point distributor. Basically, it acts as a shock-absorber for the points by preventing the point contacts from arcing as they open. If the contacts arc, they will erode and become burned. For this reason, it’s common practice to replace the condenser whenever the points are replaced. Condensers are inexpensive, and while they can be checked with the appropriate test equipment, it is usually safest to replace them. However, if you have replaced the breaker points due to normal wear or as part of a tune-up routine, and the point contacts weren’t badly burned or eroded, you may assume the condenser was okay and should keep it aboard their vehicle as a spare. Likewise, old breaker points having only normal wear may be cleaned and kept for emergency situations. Keeping old, but useable, parts is a good habit to get into if you own a vintage MV.
Setting breaker points is one of those jobs that sounds simple in a manual. Figure 5 offers a good illustration of setting the points on a WWII GMC CCKW. The process is simple: one turns the engine — preferably by hand — until a distributor cam lobe comes around and opens the breaker point contacts. After making sure that the contacts are fully open — the breaker point rubbing block is on the highest point of the cam lobe — loosen the breaker mounting screws, insert the correct size feeler gauge between the point contacts, and adjust the points so that a slight drag is felt when the feeler gauge is moved between the contacts. Then the mounting screw is retightened.
How slight is “slight is something that can only be learned from experience. A good rule of thumb is that when the point contacts are properly set, there should be only a bit of resistance when slipping the correct size feeler gauge back between the contacts. If the feeler has to be levered between the contacts, or obviously forces them open wider, then the points were set too close. If the correct size feeler gauge slips between the contacts with no resistance at all, the points have been set too wide. Of course, new points must always be set when installed.
While, again, the process is simple to describe, it is often difficult because many distributors, especially waterproof types on military vehicles, are not located in easy-to-reach places. Sometimes it’s easier to remove the distributor from the engine to install new parts or reset the points.
The rubbing block rubs against the distributor cam and thus wears away, but this wear can be lessened by keeping the cam clean and smooth. If the cam isn’t rusty or corroded, just wipe it clean all around with a rag, and then apply a bit of distributor cam grease, which may be found at most auto supply stores. A little goes a long way, so just apply a light coating all around the cam. Too much lube or any oil inside the distributor will be thrown off as the cam spins at high RPM and may collect on the point contacts and burn. It’s important to use distributor cam lubricant rather than any old grease, because ordinary grease may produce a vapor when the distributor heats up, and this vapor may collect on the point contacts and burn.
On older vehicles that sit a lot or have been in storage, the cam may be rusty. If so, it will wear the rubbing block very quickly. A rusty cam should be polished with fine crocus cloth. Be sure to get all the dust and grit out of the distributor after the cam has been cleaned.
Old points that aren’t badly eroded or burned can usually be cleaned with a special ignition points file or crocus cloth and either reset for additional use or kept aboard the vehicle. Be sure to examine the rubbing block. Even if the contacts are good, the block may be too badly worn for the point contacts to be properly set, in which case the points should be discarded. Spare points should be sprayed with something like WD-40 and wrapped in a paper towel or bit of cotton rag, also sprayed with WD-40. Small cookie tins or metal candy boxes make good storage containers for such parts. Again, if the old points weren’t badly eroded or burned, you can assume that the condenser was okay and it can be kept as a spare.
The rotor and cap are two other components of mechanical breaker point distributors that are usually replaced, or at least checked and cleaned during tune-ups,. Most M-series waterproof distributors have an inner cap inside the metal cover, which is replaced like the cap of a civilian-type distributor. Both the rotor and the contacts within the distributor cap gradually erode and burn. Like the points, if not severely worn, they can be cleaned and reinstalled, or kept as spares. If you plan to drive and use your MV, it is very important to keep any usable parts aboard. The same applies to spark plugs, whether conventional civilian types as used on most WWII MVs, or the waterproof types of M-series vehicles. They can be checked, cleaned and re-gapped with a feeler gauge rather than simply replaced, and/or kept as spares. Keep in mind that spark plug wires, even those formidable-looking waterproof types, don’t last forever and will eventually need replacement.
The coil question
What about the ignition coil? While there are rare instances of a coil becoming weak or failing to fire if it gets hot, one may usually think of a coil as being like a light bulb... it either works or it doesn’t. If it works it’s okay, if it doesn’t it can’t be fixed.
While coils, like condensers, can be tested with the appropriate equipment, they are inexpensive items so it’s usually less bother to replace them. Like a light bulb, if a coil doesn’t work, throw it away.
Compared to today’s cars and trucks, most common hobbyist military vehicles require a lot of adjustments and tinkering with. But that, too, is part of the MV experience.