Ken Cates' Hudson Stepdown Restoration Resources

RESTORATION AIDS

Ignition System

Tune Up Part Numbers

NAPA numbers

  • CAP - AL106
  • Points - CS719A
  • Condenser -  AL869
  • Rotor- AL112

NGK Plugs - B7HS

Champion H11 one step cooler plug CH10

Mallory Dual Point Distributor Hudson 232/262/308 engines

Brass Oil Pump Gear

Drives the distributor shaft - interfaces to Camshaft

Pertronix Electronic Ignition Module Installed in Hudson Distributor

Pertronix Electronic Ignition Kit for Hudson

Internal Distributor distribution wires.

Change these to prevent shorts and ignition failures

Stock Hudson Distributor

Hudson Distributor Aftermarket Dual Point installation kit

Hudson distributor

Distributor: Point Gap

Cam Angle (Dwell) Spring Tension Vacuum Advance:

MODEL 4B

.020"

38°

17-20 oz.

5° at 12" Hq 10o at 1200 RPM

5B,6B,7B

.020"

38°

17-20 oz.

4° at 8" Hq

9° at 2000 RPM

8B

017"

27°

17-20 oz 4°at16"Hq 17.5° at 1700 RPM

If you have any questions or comments e-mail me at mrriggs@gofastforless.com.

Set point ignitions

The earliest timed spark ignitions used a spring loaded mechanical switch actuated by a cam. The cam forces the switch open and the spring closes it again. The switch connects the negative lead of the ignition coil primary to ground. When the switch is closed, current flows through the primary. When the points of the switch separate, they break the circuit [I’m guessing that is why they are called breaker points, or points]. An engine will typically have one set of points but there may be multiple points hooked to multiple coils or even two sets of points hooked to one coil. When you have two sets of points on one coil it is called a dual point system. If there is only one set of points per coil then it is a single point system. Even if there are multiple coils, each with one set of points, then it is still single point.

Points are the simplest ignition system since the points are both the sensor and actuator. All you need to make a spark is a battery, a coil, and the points. Oh, and a condenser but we’ll talk more about that later. There are two types of points ignitions, battery powered and magneto. They function exactly the same; close points so current flows through primary then open points to fire coil. A battery powered ignition connects the coil primary to the battery for current. A magneto runs a magnet past the primary to generate a current inside the coil. On this page I’ll be talking about battery powered ignitions but the concepts are the same for magnetos.

Setup

Before we get in depth on the workings of a points system, you first need to know how to set one up. For points to work properly the mechanical assembly has to be in good shape. Lube everything up and check for wear. If anything is sloppy or binding then you won't get a stable dwell. A little slop is not OK. Everything must be like new for the assembly to work properly. If any of your shafts, bushings, or plates show any wear then stop reading now and find replacement parts before continuing. All shafts, bushings, and pivots need to be lubed with light oil. Don’t just squirt it with WD40 or any other “oil” that will quickly evaporate. I use spindle oil but motor oil will work. The breaker cam must be lubed with grease that won’t fly off when it’s spinning. Don’t even think about using motor oil on the cam. You can buy grease specially made for breaker cams but it’s getting harder to find. Camshaft assembly lube works well also. To make the points last longer between adjustments you should polish the breaker cam. The cam surface needs to be smooth. Any rust or gunk built up on the cam will grind away the rubbing block on the points. A fine emery cloth or Scotch Brite pad works well for getting the cam surface back to shiny metal. One thing most people don't consider when installing new points is the contact area. The two contacts should hit dead center, see picture. To align the contacts, bend the stationary breaker point bracket. Do NOT bend the breaker arm. You should also check the breaker arm spring tension, a 2 or 3 pound pocket fishing scale works well for this. Spring tension is usually 16-32 ounces depending on the application. A low rpm motor can get by with 16-20 ounces where a high rpm motor may need as much as 32 ounces to keep the points from bouncing. Higher spring tension increases the rpm range but also wears down the breaker arm rubbing block faster. If you don't rev your motor very high then lower the spring tension and your points will last a lot longer. Next you should set the gap with a feeler gauge to get it running. Turn the motor over until the points rubbing block is on the highest point of the breaker cam. At this point you will have the widest gap between the points. Check the specs for your system to find out what the gap should be. If you don’t know what the spec is, then set them at .015” which is close enough for most systems. You need to develop a feel for adjusting the gap. It’s easy to jam a thick feeler gauge into a narrow gap because the points are spring loaded. You want to adjust it so there is an ever so slight drag. This is even more difficult with a blade type gauge which if turned or tilted even slightly will make it feel like the gap is too small. A wire type gauge makes adjustment easier. The point gap effects the dwell (the amount of time current is running through the coil). The feeler gauge setting is only to get it close enough to run. When the motor is running, you can fine tune it with a dwell meter. The dwell spec is usually given as an angle. What that represents is the degrees the point cam rotates between when the points close and when they open again. A dwell meter will have a different scale for the different engine configurations. The 8 cylinder scale reads 0-45°, the 6 cylinder scale reads 0-60°, and the 4 cylinder scale reads 0-90°. An automotive dwell meter can be used on a motorcycle too if you know what the meter is actually reading. The meter is only measuring duty cycle, the percentage of time that the points are closed. A 27° dwell on an 8 cylinder is a duty cycle of 60% (27/45). If your bike has only one lump on the cam then it fires once every 360°. If the dwell spec is 90° then the duty cycle is 25% (90/360). So using the 6 cylinder scale you would set it to 15° (0.25*60). Once it is all set up, break-in the new points for a couple days, then recheck everything and make any necessary adjustments.

Pros

The biggest advantage point systems have is their simplicity. There are very few components and it’s mostly mechanical so you can see how everything works. It’s easy to wire up and the engine looks clean without extra wires and boxes. Rarely will a points ignition leave you stranded looking for parts. It most cases you can scratch the points clean with a pocket knife and gap them with a matchbook and be on your way. Since there are no electronics, a points system is not affected by electrical interference. You can run solid core plug wires and the engine won’t miss a beat.

Cons

The mechanical design of points also works to its disadvantage. When the breaker cam opens the points at high rpm, the inertia in the breaker arm will keep the points opening after reaching the high spot on the cam. Rather than riding down the back side of the cam and closing smoothly they will slam shut and even bounce. This is called point float or point bounce. Point bounce will wear out a set of points quickly and can cause the ignition to misfire. There has to be adequate spring tension to prevent the points from floating. It is this spring tension that wears out the rubbing block and causes the point gap to close up with use. Points need to be adjusted periodically to account for this wear. That is the single biggest reason for people to be either a point lover or a point hater. Some people despise having to “always be working on it” while others enjoy the ritual as part of the pleasure of keeping an old machine on the road.

The cam needs to open the points gradually to prevent float. This causes a big problem when it comes to breaking the primary circuit. Think of the points as a little 4 amp arc welder. When arc welding, you touch the electrode to your work piece, to start current flowing, and lift it up to get an arc gap. The constant current power source of the arc welder will increase the voltage to the electrode to maintain the current flow across the arc. If you keep lifting the electrode you will reach a point where the welder can not supply enough voltage to maintain the arc and current flow will stop. Points will do the exact same thing. Current flows through them when they close. When they open the inductance of the ignition coil tries to maintain that current so an arc will be struck between them until the points open up enough to break the circuit. The more current you run through the points, the harder it is for them to break the current. That is why point systems have a condenser (called a capacitor in any other electrical system). The condenser slows down the reaction time of the coil to allow the points time to open and break the circuit. Without a condenser you will likely never break the primary current and get no spark from the secondary. Having a condenser that is too large will completely prevent arcing across the points but will also slow the coil so much that it is unable to strike an arc on the secondary. The trick is to find a condenser that gives a happy medium between the arc at the points and the arc at the spark plug. A smaller condenser means more power from the coil but shorter point life due to pitting. A larger condenser will give you longer point life but sacrifice coil output. One trick to make a high performance points system is to wire two condensers together in series. This effectively gives you one condenser with half the value. Most guys when changing points will replace the condenser if it needs it or not. This is not always a good idea. A condenser is a simple component and they rarely go bad. The only bad condenser I've seen was brand new, the wire had broken off inside. If you are changing your points and the motor was running fine then do not replace your condenser. You may do more harm than good.

Another disadvantage to points is the dwell strategy. The dwell of a points system is a fixed duty cycle. On a V8 the points open every 45°. With the dwell set to 30° the duty cycle is 66.67%. That means that regardless of engine speed, there will be current flowing through the primary of the coil two thirds of the time. This chart illustrates why this is not a desirable dwell strategy. In this example it takes the coil 2.5 milliseconds to charge. The charge time of the coil is constant. Whether the engine is spinning fast or slow, it will take 2.5 milliseconds to charge the coil. At 1000 rpm the points are closed for 10 milliseconds. After 2.5 millisecond the coil is fully charged (illustrated by the dark blue line), but energy is put through the primary for an additional 7.5 milliseconds (light blue line). That energy is wasted heating up the coil. Points systems use a ballast resistor and/or high resistance coil to limit the peak current so the coil won’t burn up. That high resistance slows down the charge rate of the coil and limits the energy it can store. The pink line shows the energy put into and stored in the coil at 5000 rpm. Because the duty cycle is fixed, and because of the high primary resistance, the dwell is not long enough to fully charge the coil. If you were setting up the ignition on a generator or lawn mower where the engine ran at a constant speed then you could set the dwell to charge the coil completely without wasting energy. However, the engine in a car does not run at a constant speed so the dwell of points is almost never correct. The coil is either burning up because it was charged too long or crapping out because it wasn’t charged long enough.

Dual Points

Dual point distributors were used on high performance engines back in the day before electronic ignitions. A dual point system has two sets of points, slightly offset, driving one coil. The purpose of the dual points is to increase the dwell and allow wider point gaps. A standard Ford single point distributor has about 28° dwell with a .014" point gap. A Ford dual point has 33° with a .019" gap. The longer dwell allowed the ignition to operate at higher rpm because it gave the coil more time to charge. The wider point gap allowed it to more easily break the primary current. Since a dual point has larger point gaps it also needs higher breaker spring tension. The factory spec for a Ford dual point is 27-30 ounces.

Adjusting a dual point is a little different than single points. You need to isolate one set of points at a time to make sure they are both set to the same dwell. You also need to make sure the combined dwell is within spec. My uncle showed me a great way to adjust a dual point distributor. Hook a remote start switch to the starter solenoid and a dwell meter to the distributor. Pull the coil lead off the distributor cap and ground it to the motor. Pull off the distributor cap and rotor so you can get to the points. Place a thin piece of cardboard or plastic between one set of points so they don't make contact. Turn the motor over with the remote start switch (make sure the car is out of gear first) and read the dwell. Then move the cardboard to the other points and measure the dwell again. Adjust the points as needed until both are the same when isolated and give you the proper total dwell when combined. I adjust mine to 26° each which gave me a total of 33°.

Dual points were a good idea back when there was no better alternative. They provide slightly better performance than a single point system but suffer from all the same shortcomings. These days, electronic ignitions are cheaper and simpler than dual points and will perform much better. Single points can still be desirable in a non-performance application because they are simple and dependable, but dual points is system whose time has come and gone.

For those of you who are anti-point and feel I'm wasting web space for even mentioning them, please send hate mail to mrriggs@gofastforless.com. The rest of you, who still know a good thing when you see it, write me at mrriggs@gofastforless.com and let me know what you think.

Distributor advance

It doesn't matter what kind of ignition you have, if the advance curve is not set properly it won't make any power. The ignition is advanced so you reach peak cylinder pressure right after TDC (top dead center). If the spark comes too soon the burning fuel will try to push the piston back down the cylinder before it reaches TDC, resulting in a loss of power and possible engine damage. If the spark is too late you will not reach full power and get poor gas mileage. There are two major factors that effect how much advance is required, engine speed and load. You increase advance with rpm and decrease advance with engine load. You don't need a distributor test stand to curve a distributor. All you need are some basic hand tools, a timing light, and a tach.

The first thing you should do is find a shop manual for your particular car. Read about the advance mechanism and make yourself familiar with the different components. Before doing too much you should check the condition of your advance mechanism. If your vacuum diaphragm is bad replace it. Lube all the components and make sure they are moving freely.

You probably won't have enough timing marks to test total advance. You can buy stickers for the harmonic balancer or you can make one. I made some on my computer. If you are really cheap you could just draw lines on a piece of tape. Trace them from the timing marks you already have to get the right spacing. The easiest way is to buy a timing light with an advance dial. They are kind of spendy, about $60, but a big time saver.

The mechanical, or centrifugal, advance adjusts the timing based on engine speed. The faster the motor spins the more it will advance the timing. The factory advance curve is very conservative. By using a more aggressive advance curve you can greatly improve your engines performance. To setup your mechanical advance you first need to disconnect your vacuum advance line. Next you should hook up a tach and timing light and see what your timing is set at. Simply watch the timing marks with the light. The reading at idle is your initial advance. Rev the motor up until the distributor stops advancing and note what speed it maxes out. This is your total advance.

Total advance is the most critical setting. Short of a dyno the best way to find what total advance you need is some track tuning. The MPH reading at the end of the track is your best indicator of engine output. Make a run or two to get a baseline then increase your total advance and make another run. If the MPH increases advance it some more and run again. Continue advancing the ignition until the MPH starts falling off then pull it back to the point where you had the highest trap speed. It may take quite a few passes until you find the optimal setting. Total advance is initial advance plus mechanical advance. There are two ways to change the total, adjust the initial advance by turning the distributor or adjust the mechanical advance mechanism. The easiest, and cheapest way is to just turn the distributor until you get the total you want then just leave the initial wherever it ends up. If you want more control over the initial then you need to adjust the advance mechanism. If you have a total of 36° and want to run 12° initial then you need 24° mechanical advance. Aftermarket distributors will have replaceable bushings to adjust mechanical advance. Stock Ford distributors have two slots. There is a pin that sits in one of the slots to limit travel. To change slots you simply remove the armature assembly turn it 180 degrees and reinstall it so the pin is in the other slot. The slots are numbered as to how many distributor degrees it will pull in, double it to find the amount of crank degrees. So if you want 24° mechanical advance you need to find an armature assembly with a slot marked 12L. My distributor is setup with the stop in the slot marked 13L, this means 26° mechanical advance. The other slot is marked 18L which is 36°. I wanted less than 20° so I made the big advance spring a stop. I wrapped the coils with copper wire then soldered it so it was solid. Now I can adjust the total advance by bending the adjustment tab through the hole in the breaker plate. This makes it easier to adjust than the factory setup, and most aftermarket distributors for that matter.

Initial advance isn't very critical. Usually you just set the total where it needs to be and leave the initial wherever it ends up. Once you found the best total advance setting you can play with the initial. Basically you want to run as much as you can before the motor cranks over hard. With the motor warm pull the timing way up and try to start the motor. If it cranks real slow then pull it back until it spins normally. Lets say that is 20° and you ran best with a total of 36°, that means you need 16° mechanical advance. Any time you adjust the initial you need to adjust the mechanical advance so the total stays the same, this is easy to do with my distributor mod above. Now if you're running tall gears and/or a heavy car you will probably encounter some sort of pinging if you stand on it with that much advance. If it happens at real low engine speeds then you need to pull the initial timing back. If it happens at moderate RPM levels then you can probably fix it with the advance springs.

The springs adjust the advance rate. Where the distributor is bolted down determines the initial advance, the amount of travel in the mechanical advance determines the total advance, and the springs determine what RPM total advanced is reached. Lighter springs allow the mechanical advance to move more easily so you will reach total advance at a lower RPM. Stiffer spring will delay the total advance. Most distributors use two springs, a small one and big one. The big one will usually have a bit of lash so the small one does all the work at low speeds. This allows the advance to come up quickly off idle. Once the lash on the big spring is used up the weights will be trying to pull both springs so the advance rate will slow down. The chart below shows a typical stock advance "curve". It is the dual springs that give it the curve. If there were only one spring the chart would just be a straight line.

In this example it idles around 500 rpm and has 6°initial advance. At this point only the small spring is holding back the timing. It is a light weight spring so the advance rises fairly quickly until it hits 18° at 1800 rpm. Once you hit 18° the lash on the big spring is taken up so the advance rate levels off a bit. If you increased the lash on the big spring the advance will go further than 18° degrees before hitting the big spring, less lash will hit the big spring sooner. To adjust what rpm you hit the big spring you would change the small spring. A lighter small spring will cause you to hit the big spring before 1800 rpm and a heavier small spring will delay it until after 1800 rpm. In this example you hit total advance (28°) at 4000 rpm. As mentioned above the total is limited by the mechanical advance mechanism. The rpm total advance is reached is determined by the big spring. A heavier big spring will delay total until after 4000 rpm and a lighter big spring will allow total to come in before 4000 rpm.

If you experience pinging just off idle you should lower your initial advance. If your motor pings around the point you reach total advance you have two options; lower the total advance or put in a heavier big spring to delay the total. If its pinging well above this point you will need to pull back the total. If your motor is fine at low and high speed but pings in the mid range then you need to either reduce the lash in the big spring to lower the mid advance point or install a heavier small spring to delay the mid advance point. Making these fine adjustments can be a pain in the neck because adjusting one element often changes the others. If you want to bypass this whole mess you could use my programmable digital ignition. It allows you to adjust any of these points independent of the others and from the comfort of the drivers seat.

The mechanical advance is adjusted for high load WOT conditions. Under light load, part throttle conditions the manifold pressure is lower so volumetric efficiency is lower so the cylinder pressure is lower so the fuel mixture burns more slowly. This means you need to light the mixture sooner so you reach peak cylinder pressure at the ideal time. This is the purpose of the vacuum advance. The lower the load is the more it will advance the timing. Vacuum advance will improve gas mileage and drivability of a street driven car. A lot of guys think a vacuum advance hurts performance, this is not true. The vacuum advance is entirely independent of the mechanical advance. They are two separate systems that perform two separate functions. The mechanical adjust timing based on RPM where the vacuum adjusts timing based on load. Under high load, WOT, performance conditions there is almost no manifold vacuum so the vacuum advance does nothing. The only time the vacuum advance adds timing is at part throttle, low load conditions when there is manifold vacuum. So unless you race at half throttle a vacuum advance will have no effect on performance. It will however improve part throttle drivability so unless your car is a 100% race car I would recommend running a vacuum advance.

You're probably thinking, "Sure there is no manifold vacuum at WOT but aren't I supposed to use ported vacuum for the vacuum advance." Hold onto your hat, THEY ARE THE SAME THING! Except ported is shut off at idle. There are a lot of misconceptions when it comes to the ported vacuum source. After hearing 20 different theories I decided to hook up two vacuum gauges, one to manifold and one to ported, then drive my car and watch it. I found out they are the same, except the ported is shut off when the throttle is closed. Even then I had a hard time convincing guys so I hooked up a couple MAP sensors and a throttle position sensor to a data logger and recorded them while driving then dumped it into a spreadsheet and made a chart. As you can see, there is a direct relationship between throttle position and vacuum. When the throttle is closed vacuum is high, when the throttle is open vacuum is low, and ported vacuum is the same as manifold except when the throttle is closed. So which one do you want to hook it to? I prefer manifold vacuum. This pulls in more timing at idle which is good since there is virtually no load. Your motor will idle smoother and cooler with the extra timing. One night I was at the drags and my car was running hot in the staging lanes, I swapped the vacuum advance from ported to manifold then it would idle all night at 175°. Believe it or not the purpose of ported vacuum is to raise the temperature at idle, to lower NOx emissions. If you're like most hot rodders that is of no concern to you. If you have a big cam with a choppy idle then a vacuum advance hooked to manifold vacuum can really help. It will idle smoother and requires less throttle to maintain speed. Often a big cam requires you to open the throttle so far that the curb idle adjustment needles won't work. Hooking the vacuum advance to manifold vacuum will allow you to close the throttle some which may be enough for the idle mixture screws to work. Someone told me he noticed less dynamic braking with the vacuum advance hooked to manifold. I didn't notice it on my car but it makes sense. If the motor is running more efficiently with the added advance it will make a less effective brake. So which should you use? Try both and see which you like best.

Once you have the mechanical advance setup to give you the most power, and no pinging, at WOT then you should setup the vacuum advance. A stock vacuum advance will pull in 20° or more. If your car is pinging or running rough after hooking up your vacuum advance then you need to turn it down. Most vacuum canisters are adjusted by sticking an allen wrench in the vacuum tube. Turning the wrench counterclockwise will reduce the timing. Just turn it down a bit at a time until the problem goes away. I had to turn my vacuum advance down until it only pulled in 5°. 

If you have any questions or comments e-mail me at mrriggs@gofastforless.com.

Hudson Oil Pump with timing gear

Note slot in end, this is the distributor shaft interface point

Ultimate Hudson Distributor testing machine

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This page was updated January 2018

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