WSM.124
Section B (Engine)
STROBOSCOPIC TIMING LIGHT-Uses
The stroboscopic timing light provides a rapid and
convenient means of setting the ignition timing
and checking the action of the centrifugal and
vacuum advance action of the distributor, provided
its use is understood.
Correctly connected and with the engine running
the timing light gives a high intensity flash every
time No. I cylinder fires. When this light is
directed on to the crankshaft pulley rim, the rim
will appear to be stationary. It is this feature that
makes it such a useful piece of equipment.
Its advantages are:-
1. It Is simple to use and portable.
2. The Ignition timing can be quickly checked
while the engine is running, provided the
engine speed can be set with a tachometer.
3. It enables a quick check to be made of the
distributor centrifugal and vacuum advance
mechanism, with the distributor in position,
while the engine is running.
4. It is possible to set or check ignition timing
regardless of any backlash that may exist in the
distributor drive gears or camshaft driving
chain.
Checking Ignition Timing-with stroboscopic
timing light
THIS CANNOT BE DONE WITH THE ENGINE
IDLING because at the correct idling speeds given
in section C, pages 25 and 51, under slow running
adjustment, the distributor centrifugal advance
may have begun to operate.
It is therefore necessary to check the ignition
timing at an engine speed of 1,000 r.p.m. using a
reliable tachometer with the stroboscopic
timing light, as explained in the following proce
dure.
I. Obtain the static ignition setting from the Data
section, under ignition, noting that this is
given in crankshaft degrees.
2. Add the crankshaft centrifugal advance for a
crankshaft speed of 1,000 r.p.m. to the static
ignition setting. The centrifugal advance angle
I
st re-issue
Page 13
for this engine speed on Alpine and Rapier
engines is 3 crankshaft degrees BTDC.
Example-in crankshaft degrees
3
°
centrifugal advance BTDC
+
8
°
static advance
BTDC
=
11
°
ignition advance BTDC at 1,000 r.p.m.
3. Multiply the total number of degrees found in
paragraph 2 by 1 ·28. This gives 14 mm. which
is the number of millimetres before TDC for
11
°
BTDC on the crankshaft pulley damper
rim. Set a pair of dividers to this calculated
dimension and mark this distance before TDC
on the damper rim. Paint this position with a
narrow white line. Also paint the tip of the
fixed TDC pointer. Quick drying white paint
should be used.
Note: If the damper rim has a number of 5
°
1
spaced timing marks as shown in the inset of \
Fig. 13 it will not be necessary to mark off the i
metric measurement equivalent for 11
°
because
this angle can be read off directly on the damper
rim using the timing marks. The marks are
spaced at 5
°
intervals.
4. Connect a tachometer and stroboscopic timing
light to the engine and run it at 1,000 r.p.m.
WITH THE VACUUM ADVANCE PIPE DIS
CONNECTED FROM THE DISTRIBUTOR to
prevent any possible vacuum advance action.
5. Project the beam of the stroboscopic timing
light on to the TDC pointer on the timing case.
The white lirie on the crankshaft damper rim
should appear opposite to the TDC pointer
while the engine Is running at 1,000 r.p.m. If
necessary adjust the distributor to obtain this
condition.
Checking the centrifugal advance action-at
2,500 engine r.p.m.
First check that the static ignition timing is cor
rectly set to its average figure of 8
°
BTDC. Then
remove any line painted on the pulley rim to
correspond with this position and disconnect the
vacuum advance pipe.
On Alpine and Rapier engines the ignition centri
fugal advance angle at 2,500 r.p.i:n. is 24
°
BTDC.
Summary of Contents for ALPINE I SERIES: APLINE II SERIES
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