Changing Ignition Points, Setting Dwell, Setting Timing: 1974 and Earlier
| 01 May 2002
Getting Started
For those of you still using ignition points in Gen-1 and early Gen-2 cars, this pony trick will describe how to change points, set their dwell (gap), adjust ignition timing, and optimize the settings. It’s a relatively easy procedure. All you’ll need in addition to a set of points are a flat blade screwdriver; a small adjustable wrench or a set of ignition wrenches; a distributor wrench; and a match book, business card or feeler gauge. A dwell meter will also be required if you chose to optimize dwell (point gap).
To start the job, make sure the ignition switch is turned off and then identify which spark plug wire in the distributor cap goes to no. 1 cylinder. No. 1 on the V-6s and V-8s is at the right (passenger’s side) front corner of the engine while on the inline 4s and 6s it’s closest to the radiator. Plug wires correctly placed in the distributor cap will have no.1 immediately to the driver’s side of the rear cap-clip on the V-8s, half-way between the two clips and toward the passenger’s side on the V-6s, half-way between the two clips and toward the driver’s side on the inline 6s, and approximately half-way between the two screws and toward the driver’s side on the inline 4s. It’s possible for the wires to be installed differently so verify the position on your car. Don’t change anything, just verify.
Next remove the distributor cap by releasing the clips (or screws). Move the cap and the spark plug wires aside to give you clear access inside the distributor. Leave the rotor button in place for now. With the transmission in park or neutral (MAKE SURE IT’S OUT OF GEAR), bump the starter (small bumps are good) until the rotor button points toward the no. 1 cylinder position you identified. The rotor turns clockwise in the 4s and 6s and counter-clockwise in the 8s. As the rotor approaches no.1 position, look for the timing mark(s) on the harmonic balancer or crankshaft pulley and continue to bump the starter until the timing pointer and the timing mark line up at the correct position. The location and appearance of the pointer and marks will depend on which engine you have. The correct position is the timing specification for your engine. For your specific car, you'll need to know what that is but for our purposes here, we'll assume that it’s 6-degrees BTDC (before top dead center). So what we’re trying to do in this example is align the pointer and the mark at 6 degrees BTDC. If you miss the alignment, continue bumping the starter until the rotor makes two more revolutions and try again. You can bump the starter with a remote starter button connected at the starter solenoid between the hot lead from the battery and the terminal where the small red wire plugs onto the engine-bay side of the solenoid or you can have a helper bump the starter from the ignition switch while you watch the rotor and timing marks.
It’s not unusual to miss the timing mark several times before the engine stops in the right position. If you have easy access to your fan belt near the crankshaft pulley, there’s a trick you can use to ease the frustration. Stop bumping the starter when you see the rotor button approaching no. 1 and the timing marks nearly aligned. If a helper was bumping the starter for you, have them turn the ignition off and get out of the car. Grasp the fan belt near the crankshaft pulley and rotate the engine the last little bit by pulling on the belt until the marks are aligned. If you do this, it’s important to rotate the engine in the same direction that it runs: clockwise as you’re standing in front of it. If you go beyond the mark when you pull on the belt, back the engine up by pulling the belt in the other direction. Be sure to back it up an inch or two beyond the mark so you can pull it forward again ( in the running direction) for the final alignment.
When the timing marks are aligned, remove the rotor, remove the point-set and disconnect the wires from the points, install the wires on the replacement point-set, and install the point-set into the distributor. Tighten the point-set retaining screws to a light pressure but not so tight that the set can’t be moved. Adjustments are next.
Setting Dwell and Timing
Later in this article we’ll adjust dwell and timing with a dwell meter and a timing light. But first, we’ll adjust point gap and set the timing without using the meter or the light. This method results in acceptable settings for day-to-day street driving. We’ll do point gap first. Gap (or dwell) is always adjusted before setting the timing because a change in gap causes a change in timing.
Mark the distributor location by scribing a line on its flange and the adjacent engine area using a screwdriver or a sharp instrument. Using a distributor wrench, loosen the distributor holddown clamp just enough so the distributor can be rotated and then turn the distributor a few degrees so that the point-set rubbing block is on the peak of a cam lobe. With the block resting on the lobe, adjust the points to a gap that equals two thicknesses of a matchbook cover or two thicknesses of a business card (about 0.022 inches) and then use the screwdriver to tighten the point-set to the breaker plate. The point gap specification would typically be in the range 0.025 to 0.027 inches for the 4-cylinder and 6-cylinder engines and 0.017 to 0.021 inches for the 8-cylinder engines but 0.022 works well enough if you don’t have access to a feeler gauge. If you have a feeler gauge, than set the gap according to the specification for your engine. Finally, turn the distributor body back to its starting position so that the scribe marks are aligned. Next we’ll set the timing.
Rotate the distributor in the direction the rotor turns when the engine is running (clockwise for 4s and 6s and counterclockwise for 8s); move it only far enough so that the point-set-rubbing-block is located about half way between cam lobes. Turn the ignition switch to the “on” position being careful that you don’t engage the starter. Now slowly rotate the distributor body in the direction opposite to its running rotation. As the rubbing block approaches the cam lobe, watch for (and listen for) a slight spark at the ignition-point contacts. In bright sunlight, shade the contacts for better visibility. When the spark occurs, the points have started to open and you’ve found the timing position. You may want to repeat the procedure two or three times to get as close as possible to the position where the points just begin to open. When you’re satisfied that you’ve done your best, hold the distributor in place and tighten the holddown clamp.
You can also use a multimeter to read voltage or a 12v test-lamp to detect when the points begin to open. Connect the meter or the lamp between engine-ground and the wire-terminal on the point-set. As you approach the cam lobe while rotating the distributor opposite to running direction, the test lamp will glow or the multimeter will indicate voltage when the points start to open. This is the same position where the spark occurs in the preceding paragraph. It’s just an alternate and somewhat easier way to find the timing position.
New points usually come with a small capsule of lubricant. Apply it to the cam lobes with your finger tip so the rubbing block can pick it up as the cam rotates. To enhance the electrical connection between the point-set contacts, you may want to burnish them by inserting cardboard from a matchbook cover between them and sliding it up and down a few times. With all adjustments made, all fasteners tightened, lubricant applied, and the points burnished, install the rotor and distributor cap to complete the job. If you used a remote starter button, be sure to remove it from the starter solenoid and connect the small red wire to the solenoid, if it was disconnected. Now you’re ready for a test drive.
The tricks explained in part-1 and part-2 of this 3-part series have probably resulted in settings that are “close enough” for many applications. Even so, optimization should be considered. Timing optimization, in particular, can benefit most cars. Part-3 will cover optimization of gap and timing.
Optimizing Dwell and Timing
The static (engine not running) settings described above can be optimized using a dwell meter and a timing light. This is a dynamic procedure where adjustments are made with the engine running. The dwell meter is required for point-gap optimization and the timing light is typically used to set the timing. However, in this procedure we’re going to use the dwell meter but not the timing light. A vacuum gauge or a tachometer would come in handy but neither one is required. We’ll begin by adjusting point dwell because as you’ll recall, a change in dwell (gap) alters the timing. So timing must be set last.
Point gap is a passive way of arriving at dwell. But we want an active way to measure dwell, dwell or dwell angle being the number of degrees of distributor shaft rotation during which the points remain closed between encounters with adjacent distributor cam lobes. When dwell is set to specification, it provides optimum time for the coil primary-circuit to saturate prior to a spark event. You’ll need to look-up the correct dwell angle for your engine before starting this procedure.
To measure dwell, connect the dwell meter per the manufacturer’s instructions and start the engine. If the dwell angle is greater than the specification for your engine, stop the engine, remove the distributor cap, loosen the point-set, and increase the gap; if dwell is less than spec, decrease the gap. Tighten the points, install the distributor cap, and start the engine again to check the “new” dwell angle. Continue making adjustments until the dwell angle is correct. You’ll notice that small adjustments change the dwell a noticeable amount so move the points in very small increments as you search for the correct setting. You’ll also find that it’s easier to control your adjustments if the point-set rubbing block is between cam lobes; i.e., it’s not resting on a lobe. If the dwell specification for your engine is expressed as a range, try to set it at the lower end of the range to allow for rubbing-block wear. When the angle is correct, move on to timing optimization. Skip this dwell angle procedure if you don’t have a dwell meter but perform the timing optimization anyway.
As already noted, when the timing was previously set to a static position because the engine wasn’t running. Usually, a slightly more accurate setting can be achieved using a timing light with the engine running at specified idle speed and all vacuum signals disconnected (and plugged) from the distributor but static and timing-light procedures both assume that timing marks and timing pointers are accurate. That may not be true on older engines, especially when timing marks are on the harmonic balancer. The marks may be close enough for day-to-day use or they may be so far off that poor power delivery or pinging is evident even when timing is carefully set according to spec. That’s because the outer ring of the harmonic balancer is mounted to rubber and it can move. Timing optimization will compensate for timing mark inaccuracies.
Make sure the gasoline in the tank has the octane rating that you plan to use. If you have a vacuum gauge, connect it to a port on the intake manifold or you can use a tachometer connected to the distributor side of the coil primary-circuit. Loosen the distributor holddown clamp so the distributor can be rotated with a slight effort. Start the engine and then slowly rotate the distributor in the direction the rotor turns (clockwise for 4s and 6s and counterclockwise for 8s). That will retard the timing and cause the engine to slow down. Vacuum should also drop off. When the engine starts to slow, begin to advance the timing by slowly turning the distributor in the opposite direction; i.e., counter to its running direction. Engine speed and the vacuum signal should both increase to a maximum and then begin to fall off again. Also the engine will begin to lope or run rough. Timing is too far advanced when this occurs so reverse direction again. Slowly rotate the distributor back to a smooth idle at the maximum readings you saw. If you’re working without either a vacuum gauge or a tach, rotate it back to where the engine smooths-out and sounds like its at the highest speed you heard. Rotate the distributor back and forth two or three times to satisfy yourself that you’ve found the point of highest engine speed and smooth idle. Now tighten the distributor holddown clamp and take the car for a test drive. Take your distributor wrench with you for final adjustments on the road.
What you’re looking for is very slight pinging (audible detonation) when the engine is working under moderate to heavy load in high gear so it will be helpful if you can find a hill or incline that you can climb at moderate highway speed. If you have an automatic transmission make sure you stay in high gear (no passing gear). Accelerate to place the engine under load and listen for pinging. If you hear pinging, stop and retard the timing a small amount; continue testing and adjusting until the pinging just goes away. If there is no pinging, stop and advance the timing in small increments until pinging begins. Reverse the process as explained above until the pinging just goes away. Timing is optimized when it is as far advanced as the engine will tolerate without pinging. If at the optimized setting kickback is experienced when starting the engine, subsequent incremental distributor rotation to slightly retard the timing may be required.
That’s it. The procedure is complete. After you’ve done it a couple of times it should be quite easy and not very time consuming.