3.
i
SPeciFication
Model no: ......................................................................tL93
Measures .....................................................................range
Advance: ..............................................................0-60
0
BtDc
tach: .................................................................200-9990rpm
Dwell Accuracy: .........................................................0-99.9%
Voltage: .................................................................. 0-16V Dc
4. what iS timing?
imPoRtant:
Always switch off the ignition before doing the following:
- connecting motor testing instruments
- replacing ignition systems components
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 the explosion must be timed so that maximum force is delivered to the engine’s piston. this is
“timing”. Each engine manufacturer tells its factory the exact timing necessary for various engines so that every possible amount of
power is obtained from each litre of fuel. As normal engine and ignition systems wear, the timing can change, thereby reducing both
power and mileage. With the tL84 or tL85 timing Light, you can reset the timing to the manufacturer’s standard, regain lost power and
increase mileage.
timing is given in Degrees Before top Dead centre (BtDc) or After top Dead centre (AtDc). in order to completely burn the air/fuel
mixture in the car’s cylinders, most timing is such that the spark occurs at a point several degrees BtDc (for example 4
°
BtDc). this
ensures that the full power of the is explosions obtained (see fig 1).two additional terms used when describing timing are ‘Advanced’ and
‘retarded’.
As shown in figure 1, when the timing is advanced the spark will occur BtDc. on some late model cars equipped with various emission
control devices, the timing is retarded so that the spark occurs AtDc. timing is changed by adjustment of the ignition distributor.
in order to allow setting and adjustment of the engine timing, timing marks are provided on each engine during assembly. in most cases,
these marks appear on the engine vibration damper or fan pulley at the lower front of the engine (figure 1). on some early engines, this
mark was shown at the rear of the engine on the flywheel.
4.1.
when to checK timing
the instant of the spark plug firing is determined by the closing of the distributor ignition breaker points and will change any time the
points gap or dwell angle is changed. in addition, normal wear on the breaker point rubbing block will change the dwell and affect the
timing. cars equipped with the new “breakerless electronic ignition system” will not normally change timing since there are no breaker
points. for these vehicles, 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.
4.2.
timing SPeciFicationS
As noted earlier, timing requirements vary from engine to engine. the engine manufacturer’s specifications should always be referred to
before making any adjustment. these specifications can be found in the cars owner manual, on the under bonnet decal required on all
cars manufactured since 1968 and in various automotive publications.
5. oPeRation
5.1.
Bring the engine to operating temperature. Make sure that the contact breaker points of the dwell angle are correctly adjusted.
5.2.
use your owner’s manual to determine the pertinent technical data of your vehicle (e.g. rpm, dwell angle).
5.3.
Locate engine timing mark (see fig.1) and use 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 visible.
5.4.
two marks are needed for adjusting the timing:
1.
A fixed mark on the engine housing, usually a pin, arrow or graduated scale.
2.
A rotating mark on the flywheel or on the crankshaft pulley, mostly in the form of a notch, a steel ball or a graduated scale.
imPoRtant:
the above marks are usually in the vicinity of hot and rotating parts. Be careful of the exhaust manifolds, fan blades,
Original Language Version
© Jack sealey Limited
Fig.1
tL93.V2 issue 2 (H, f) 16/02/18
