Certain 1975-77 and virtually all 1978 and later Datsuns are equipped with electronic, breakerless ignition systems. See the following section for maintenance procedures.
The points function as a circuit breaker for the primary circuit of the ignition system. The ignition coil must boost the 12 volts of electrical pressure supplied by the battery to as much as 25,000 volts in order to fire the plugs. To do this, the coil depends on the points and the condenser to make a clean break in the primary circuit.
The coil has both primary and secondary circuits. When the ignition is turned on, the battery supplies voltage through the coil and onto the points. The points are connected to ground, completing the primary circuit. As the current passes through the coil, a magnetic field is created in the iron center core of the coil. When the cam in the distributor turns, the points open, breaking the primary circuit. The magnetic field in the primary circuit of the coil then collapses and cuts through the secondary circuit windings around the iron core. Because of the physical principle called electromagnetic induction, the battery voltage is increased to a level sufficient to fire the spark plugs.
When the points open, the electrical charge in the primary circuit tries to jump the gap created between the two open contacts of the points. If this electrical charge were not transferred elsewhere, the metal contacts of the points would start to change rapidly.
The function of the condenser is to absorb excessive voltage from the points when they open and thus prevent the points from becoming pitted or burned.
If you have ever wondered why it is necessary to tune-up your engine occasionally, consider the fact that the ignition system must complete the above cycle each time a spark plug fires. On a 4-cylinder, 4-cycle engine, two of the four plugs must fire once for every engine revolution. If the idle speed of your engine is 800 revolutions per minutes (800 rpm), the breaker points open and close two times for each revolution. For every minute your engine idles, your points open and close 1,600 times (2X800=1,600). And that is just at idle. What about at 60 mph-
There are two ways to check breaker point gap: with a feeler gauge or with a dwell meter. Either way you set the points, you are adjusting the amount of time (in degrees of distributor rotation) that the points will remain open. If you adjust the points with a feeler gauge, you are setting the maximum amount the points will open when the rubbing block on the points is on a high point of the distributor cam. When you adjust the points with a dwell meter, you are measuring the number of degrees (of distributor cam rotation) that the points will remain closed before they start to open as a high point of the distributor cam approaches the rubbing block of the points.
If you still do not understand how the points function, take a friend, go outside, and remove the distributor cap from your engine. Have your friend operate the starter (make sure that the transmission is not in gear) as you look at the exposed parts of the distributor.
There are two rules that should always be followed when adjusting or replacing points. The points and condenser are a matched set. Never replace one without replacing the other. If you change the point gap or dwell of the engine, you also change the ignition timing. Therefore, if you adjust the points, you must also adjust the timing.INSPECTION
A dual breaker point distributor was used on the 610 in 1973 as part of the emissions control system. The point sets are wired parallel in the primary ignition circuit. The two sets have a phase difference of 7°, making one a retard set and the other an advance. Ignition timing is advanced or retarded depending on which set is switching. Which set the engine operates on is controlled by a relay which in turn is connected to throttle position, temperature, and transmission switches. The dual points are adjusted with a feeler gauge in the same manner as the single point distributor.
- Mark and disconnect the high tension wire from the top of the distributor and the coil.
- Remove the distributor cap by prying off the spring clips on the sides of the cap.
- Remove the rotor from the distributor shaft by pulling it straight up. Examine the condition of the rotor. If it is cracked or the metal tip is excessively worn or burned, it should be replaced. Clean the tip with fine emery paper, or equivalent.
It is a good idea at this time, to check the distributor cap for small cracks as this will affect the performance of the engine.
- Pry open the contacts of the points with a screwdriver and check the condition of the contacts. If they are excessively worn, burned or pitted, they should be replaced.
- If the points are in good condition, adjust them and replace the rotor and the distributor cap. If the points need to be replaced, follow the replacement procedure given below.
- Mark or tag then remove the coil high tension wire from the top of the distributor cap. Remove the distributor cap and place it out of the way. Remove the rotor from the distributor shaft by pulling up.
- On single point distributors, remove the condenser from the distributor body. On early dual point distributors, you will find that one condenser is virtually impossible to reach without removing the distributor from the engine. To do this, first note and mark the position of the distributor on the small timing scale on the front of the distributor. Then mark the position of the rotor in relation to the distributor body. Do this by simply replacing the rotor on the distributor shaft and marking the spot on the distributor body where the rotor is pointing. Be careful not to turn the engine over while performing this operation.
- Remove the distributor on dual point models by removing the small bolt at the rear of the distributor. Lift the distributor out of the block. It is now possible to remove the rear condenser. Do not crank the engine with the distributor removed.
- On single point distributors, remove the points assembly attaching screws and then remove the points. A magnetic screwdriver or one with a holding mechanism will come in handy here, so that you don't drop a screw into the distributor and have to remove the entire distributor to retrieve it. After the points are removed, wipe off the cam and apply new cam lubricant. If you don't, the points will wear out in a few thousand miles.
- On dual point distributors, you will probably find it easier to simply remove the points assemblies while the distributor is out of the engine. Install the new points and condensers. You can either set the point gap now or later after you have reinstalled the distributor.
- On dual point models, install the distributor, making sure the marks made earlier are lined up. Note that the slot for the oil pump drive is tapered and will only fit one way.
- On single point distributors, slip the new set of points onto the locating dowel and install the screws that hold the assembly onto the plate. Don't tighten them all the way yet, since you'll only have to loosen them to set the point gap.
- Install the new condenser on single point models and attach the condenser lead to the points.
- Set the point gap and dwell (see the following information).
Single Point Distributor
- If the contact points of the assembly are not parallel, bend the stationary contact so that they make contact across the entire surface of the contacts. Bend only the stationary bracket part of the point assembly; not the movable contact.
- Turn the engine until the rubbing block of the points is on one of the high points of the distributor cam. You can do this by either turning the ignition switch to the start position and releasing it quickly (bumping the engine) or by using a wrench on the bolt which holds the crankshaft pulley to the crankshaft.
- Place the correct size feeler gauge between the contacts (see the Tune-Up chart). Make sure that it is parallel with the contact surfaces.
- With your free hand, insert a screwdriver into the eccentric adjusting screw, then twist the screwdriver to either increase or decrease the gap to the proper setting.
- Tighten the adjustment lockscrew and recheck the contact gap to make sure that didn't change when the lockscrew was tightened.
- Replace the rotor and distributor cap, and the high tension wire which connects the top of the distributor and the oil. Make sure that the rotor is firmly seated all the way onto the distributor shaft and that the tab of the rotor is aligned with notch in the shaft. Align the tab in the base of the distributor cap with the notch in the distributor body. Make sure that the cap is firmly seated on the distributor and that the retainer clips are in place. Make sure that the end of the high tension wire is firmly placed in the top of the distributor and the coil.
The two sets of breaker points are adjusted with a feeler gauge in the same manner as those in a single point distributor, except that you do the actual adjusting by twisting a screwdriver in the point set notch. Check the Tune-up Specifications chart for the correct setting. Both are set to the same opening.DWELL ADJUSTMENT
The dwell angle or cam angle is the number of degrees that the distributor cam rotates while the points are closed. There is an inverse relationship between dwell angle and point gap. Increasing the point gap will decrease the dwell angle and vice versa. Checking the dwell angle with a meter is a far more accurate method of measuring point opening than the feeler gauge method.
After setting the point gap to specification with a feeler gauge as previously described, check the dwell angle with a meter. Attach the dwell meter according to the manufacturer's instruction sheet. The negative lead is grounded and the positive lead is connected to the primary wire terminal which runs from the coil to the distributor. Start the engine, let it idle and reach operating temperature, and observe the dwell on the meter. The reading should fall within the allowable range. If it does not, the gap will have to be reset or the breaker points will have to be replaced.
Dwell can be checked with the engine running or cranking. Decrease dwell by increasing the point gap; increase by decreasing the gap. Dwell angle is simply the number of degrees of distributor shaft rotation during which the points stay closed. Theoretically, if the point gap is correct, the dwell should also be correct or nearly so. Adjustment with a dwell meter produces more exact, consistent results since it is a dynamic adjustment. If dwell varies more than 3° from idle speed to 1,750 engine rpm, the distributor is worn.Single Point Distributor
- Adjust the points with a feeler gauge as previously described.
- Connect the dwell meter to the ignition circuit as according to the manufacturer's instructions. One lead of the meter is connected to a ground and the other lead is connected to the distributor post on the coil. An adapter is usually provided for this purpose.
- If the dwell meter has a set line on it, adjust the meter to zero the indicator.
- Start the engine.
Be careful when working on any vehicle while the engine is running. Make sure that the transmission is in Neutral and that the parking brake is applied. Keep hands, clothing, tools and the wires of the test instruments clear of the rotating fan blades.
- Observe the reading on the dwell meter. If the reading is within the specified range, turn off the engine and remove the dwell meter.
If the meter does not have a scale for 4-cylinder engines, multiply the 8-cylinder reading by two.
- If the reading is above the specified range, the breaker point gap is too small. If the reading is below the specified range, the gap is too large. In either case, the engine must be stopped and the gap adjusted in the manner previously covered. After making the adjustment, start the engine and check the reading on the dwell meter. When the correct reading is obtained, disconnect the dwell meter.
- Check the adjustment of the ignition timing.
Adjust the point gap of a dual point distributor with a dwell meter as follows:
- Mark and disconnect the wiring harness of the distributor from the engine wiring harness.
- Using a jumper wire, connect the black wire of the engine side of the harness to the black wire of the distributor side of the harness (advance points).
- Start the engine and observe the reading on the dwell meter. Shut the engine off and adjust the points accordingly as previously outlined for single point distributors.
- Disconnect the jumper wire from the black wire of the distributor side of the wiring harness and connect it to the yellow wire (retard points).
- Adjust the point gap as necessary.
- After the dwell of both sets of points is correct, remove the jumper wire and connect the engine-to-distributor wiring harness securely.