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1.
Locate engine‐timing mark, see figure 1. Us a rag to clean all grease and dirt from the mark and
the pointer. It may help to use chalk or white paint on the marks to make them more easily seen.
2. Check manufacturer’s specifications for correct timing for engine being serviced.
3. Start and run engine until normal operating temperature is reached. Approximately 15 minutes.
Stop engine.
4.
If specifications require, locate the vacuum line going to the ignition distributor vacuum
advance and disconnect and plug the line. A golf tee or small pencil may be used to seal the line.
5. Connect the timing light as shown in figure 2.
6. Start engine and operate at normal idle speed. Aim the timing light at the timing mark, be
cautious of moving parts.
7. Trigger the timing light and observe the reading from timing mark.
CAUTION: Use care when working around moving engine. The stroboscopic action will make
moving parts appear to be in slow motion. Keep hands, tools and timing light clear of moving
fan, belts or other moving parts.
GENERAL OPERATING PROCEDURES CONT.
WHAT IS TIMING?
In order for an automobile engine to function, three things are necessary: air, fuel, and a spark to
ignite the air/fuel mixture and create an explosion. The precise instant of that explosion must be
such that the maximum power is delivered to the engine piston. This is “Timing.” Each engine
manufacturer determines at the factory the exact timing necessary for various engines so that each
ounce of power is obtained from every gallon of fuel. Due to normal engine and ignition system wear,
the timing can change and will reduce both power and mileage. With the Xenon timing light, the car
owner can reset the timing to the new car standards and regain lost power and increase mileage.
Timing is given in degrees Before Top Dead Center (BTDC) or After Top Dead Center (ATDC) in the
manufacturer’s specications. In order to completely burn the air/fuel mixture in the car’s engine cyl-
inders, most timing is such that the spark occurs at a point several degrees before top dead center
(for example, 4 BTDC) to assure that full power of the explosion is obtained. Two additional terms
that manufacturers use when describing timing are; “Advanced” and “Retarded.” When the timing is
advanced, the spark will occur before the piston reaches the top of the engine cylinder (BTDC). On
some late model cars equipped with various emission control devices, the timing is retarded so that
the spark occurs after the piston has started down in the cylinder (ATDC). Engine timing is changed
by adjustment of the ignition distributor.
In order to allow setting and adjustment of the engine timing, special “Timing Marks” are provided on
each engine during assembly. In most cases, these marks appear on the engine harmonic balancer
attached to the crank pulley at the lower front of the engine.
WHEN TO CHECK TIMING
The instant of spark plug ring is determined by the opening of the distributor ignition breaker points
and will change any time the point gap or dwell angle is changed. In addition, normal wear on the
breaker point‐rubbing block will have the same aect on the point gap or dwell angle. While cars
equipped with the new “breaker less Electronic ignition Systems” will not normally change timing
since there are no breaker points, the timing light can still be used to note changes in timing caused
by troubles in the ignition system as well as for resetting timing when components are changed or
the vehicle is tuned.
8. Compare reading obtained in step 7 with manufacturers specifications. If timing is not as
specified readjust as described in the following procedure
9. Stop engine.
TIMING SPECIFICATIONS
As noted in earlier paragraphs, timing requirements vary from engine to engine and for this reason
the engine manufacturer’s specification‐should always be referred to before making and adjustment.
These specifications are contained in the car owner’s manual, and typically on the under hood decal
specifications.
GENERAL OPERATING PROCEDURES
INSTRUCTIONS
Adjusting Timing to Specification
1. Loosen distributor hold down locking bolt located at base of distributor enough so that
distributor may be rotated back and forth, Do not over loosen or remove bolt but leave tight
enough to prevent distributor from turning by itself.
2. Start and warm engine to normal operating temperature
3. Direct timing light flash at timing marks and slowly rotate distributor right and left until timing
marks re aligned with pointer to factory spec., see figure 1 above.
4. Stop engine.
5. Tighten distributor hold down bolt‐using care not.
6. Start engine and recheck timing.
To use an advance timing light for checking the “Idle Timing”
Adjust the advance to 0 (zero) on the timing light with the + an – buttons located on the back of the
timing light, see figure 3.
Follows the “Operating Procedures In General” from above.
1. Pull the trigger on the timing light, point the light at the timing mark on the vehicle.
2. Use the + or – buttons on the timing light see fig. 3, to move the mark to the 0 (zero) line on the
harmonic balancer in fig. 4
3. Look at the figure on the back of the timing light, this is your Idle Timing.
Checking the Centrifugal Advance and Vacuum Advance
1. Follows the “Operating Procedures In General” from above, except increase the engine speed
to 2000 rpm. Refer to factory owner’s manual for the recommended rpm.
2. Trigger the timing light and use the + an – buttons located on the back of the timing light. Stop
when the timing mark moves to TDC or O position.
3. Look at the figure on the back of the timing light, add this to your idle timing figure. This is
your Total Timing.
4. Compare the reading with manufacturer’s specification.
Fig. 1
Fig. 2
Fig. 3
Fig. 4
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