The ignition timing is a specification that is used to describe when a spark plug receives a high-energy voltage relative to the position of the piston. A piston that is at the top of its stroke is referred to as being at Top Dead Center (TDC). The piston in an internal combustion engine simply moves up and down in the cylinder bore of the engine block, and is attached to the crankshaft via the connecting rod. If the crankshaft is rotated one complete revolution, the piston will move two strokes, one downward stroke and one upward stroke. During the upward stroke of the piston, its position, relative to the top of its stroke is referred to as being Before Top Dead Center (BTDC). One complete revolution of the crankshaft is the equivalent to 360° of rotation. When a piston is at TDC, this position is referred to as the 0° position. If the crankshaft is rotated 1 / 2 a revolution, it has been rotated 180° and the piston would be at the bottom of its stroke.
Because the piston moves up or down as the crankshaft is rotated, the piston's location relative to TDC can be measured using the number of degrees of crankshaft rotation before the piston reaches TDC. The upward movement of the piston as it approaches TDC is referred to as Before Top Dead Center (BTDC). The ignition timing specifications provided by the manufacturer and used in this guide are provided in degrees Before Top Dead Center (BTDC).
When the spark plug receives the high-energy voltage, the intensity of this voltage is enough that the voltage jumps the gap of the spark plug creating a spark. This spark is used to ignite the fuel air-mixture in the combustion chamber. As the fuel burns, it expands, creating energy and pressurizes the combustion chamber. This pressure presses on the top of the piston, pressing it downward on a power stroke, which transmits the energy through the connecting rod to the crankshaft.
For an engine to run properly and efficiently, the correct ignition timing is essential. If the ignition spark occurs too late during the piston's upward stroke, the ignition timing is referred to as being retarded. If the ignition spark occurs too early in the piston's upward stroke, the ignition timing is referred to as being advanced.
The engine's timing requirements change as the engine speed increases and as throttle position varies. The Honda products covered in this guide use an electronic ignition system, which monitors the engine's operating conditions, and changes the ignition timing accordingly. These engines use a distributor to provide the high-energy ignition voltage to the spark plugs. On these models, the ignition timing advance is controlled by the engine control units, however the idle speed ignition timing (base ignition timing) can be adjusted by placing the engine control unit in an adjust mode moving the distributor.
If the ignition timing is set too far advanced (BTDC), the ignition and expansion of the fuel in the cylinder will occur too soon and tend to force the piston down while it is still traveling up. This condition may causes engine detonation or ping. If the ignition timing is too far retarded After Top Dead Center, (ATDC), the piston will have already passed TDC and started on its way down when the fuel is ignited. This will cause the piston to be forced down for only a portion of its travel. This will result in poor engine performance and lack of power.
On vehicles with distributors, the ignition timing should be checked during a tune-up. Usually, once the timing is set it is not likely to change. On vehicles with distributorless ignition systems, the ignition timing can only be checked using expensive, specialized diagnostic equipment. Due to its cost and complexity, the use of such equipment is beyond the scope of this guide. The ignition timing on the distributorless ignition system cannot be adjusted and the system requires no maintenance aside from replacing spark plugs. The ignition timing will remain correct as long as the sensors and control unit function properly.
The ignition timing marks are small notches located on the perimeter of the drive belt pulleys mounted on the engine's crankshaft. The engine cover above the pulleys has a pointer that is used to align with the timing notches. Two of the notches in the crankshaft pulley are painted. The notch that is painted white is TDC, (0° mark). The notch that is painted red is the idle speed ignition timing mark. On models where the crankshaft rotates in a counterclockwise direction, while facing the drive pulleys, the red idle speed ignition timing mark is located to the left of the white TDC mark. The painted red ignition timing notch also has notches on either side of it. These notches, on either side of the red notch, represent 2° increments. As long as the idle speed ignition timing occurs somewhere between these two notches, the ignition timing is within specification. For example, the idle speed ignition timing for the 1.6L is 16° BTDC plus or minus 2° . The notches on either side of the red notch on the crankshaft pulley would indicate the following information. The notch to the right of the red notch would be 16° minus 2° , or 14° . The notch to the left of the red notch would be 16° plus 2° , or 18° . As long as the idle speed ignition timing for this example, occurs between these two marks (14° -18° ), the idle speed ignition timing is considered to be within the recommended specification.
There are three basic types of timing lights available. The first is a simple neon bulb with two wire connections. One wire connects to the spark plug terminal and the other plugs into the end of the spark plug wire for the No. 1 cylinder, thus connecting the light in series with the spark plug. This type of light is dim and must be held very closely to the timing marks to be seen. Sometimes a dark corner has to be sought out to see the flash at all. This type of light is very inexpensive. The second type is powered by the vehicle's battery, by correctly connecting two alligator clips to the battery terminals. These timing lights are available with or without an inductive pickup. If the timing light does not have an inductive pickup, a wire must make physical contact with the ignition wire for the No. 1 spark plug. Using this type of arrangement usually requires the use of an adapter either at the spark plug or distributor cap connection. This tends to render this type of arrangement to be awkward, less convenient and time consuming to use.
A timing light with an inductive pickup is much easier to use. Simply connect the lead properly at the vehicle's battery and then clamp the inductive pickup around the ignition wire for the No. 1 spark plug. This type is a bit more expensive, but it provides a nice bright flash that can be easily seen, even in bright sunlight. It is easy to use, and the type most often seen in professional shops. The third type replaces the battery power source with 115-volt current. They work well, but are much less portable and convenient to use.
Some timing lights may have other features built into them, such as ignition advance checking devices, dwell meters, or tachometers. These are convenient, in that they reduce the tangle of wires under the hood, but may duplicate the functions of other tools and the features add to the expense of the tool. A timing light with an inductive pickup should always be used on Honda ignition systems when checking/adjusting ignition timing.
- If equipped with an automatic transaxle, place the shifter in Park or Neutral. If equipped with a manual transaxle place the shifter in Neutral. Make sure to apply the parking brake and block the drive wheels.
- With the heater off and in the full cold position, start the engine and hold the engine speed at 3000 rpm, until the radiator fan comes on at least one time. To check the ignition timing, the engine must be at idle speed and at normal operating temperature. Make sure all electrical consumers (defroster, radio, air conditioning, lights, etc.,) are turned OFF.
- Locate the blue plastic Service Check (SCS) Connector:
- Connect the SCS service connector tool number 07PAZ-0010100 or equivalent to the service connector.
A paper clip can be substituted for the tool by forming a "U" shaped bend in the paper clip and carefully inserting it into the back side of the SCS service connector terminals. The purpose of the tool is simply to connect the two wires together temporarily.
- Connect a timing light to No. 1 ignition wire and point the light toward the pointer on the timing belt cover.
- Check the idle speed and adjust if necessary.
- The red mark on the crankshaft pulley should be aligned with the pointer on the timing belt cover.
The white mark on the crank pulley is Top Dead Center (TDC).
- Adjust the ignition timing by loosening the distributor mounting bolts and rotating the distributor housing to adjust the timing. Set as follows:
- The timing should be set at 12° BTDC plus or minus 2° (10° -14° ) at 650-750 rpm
- Tighten the distributor bolts to 13 ft. lbs. (18 Nm) and recheck the timing.
- Remove the SCS service connector or the substituted paper clip from the SCS service plug.