Chevrolet 10 Series 1970 Service Manual page 418

ENGINE-ELECTRICAL 6Y-26
Setting D w ell A ngle
Four and Six Cylinder Engine Distributor
The point opening of new points can be checked with a
fe e le r gauge, but the use o f a fe e le r gauge on rough or
uncleaned used points is not recom m ended since accurate
m echanical gauging cannot be done on such points (fig. 6i)
Contacts points must be set to the p rop er opening.
P oin ts set too close may tend to burn and pit rapidly.
P oin ts with e x ces sive separation tend to cause a weak
spark at high speed. P r o p e r point setting fo r all m odels
are:
.019" fo r new points
.016" fo r used points
New points must be set to the la r g e r opening as the
rubbing block w ill w ear down sligh tly while seating to the
cam. Contact points should be cleaned b efore adjusting if
they have been in s e r v ic e .
T o adjust the contact point opening:
1. If n ecessary, align points (fig . 7i) by bending the
fixed contact support. Do not bend the b reak er le v e r.
F ig . 8 i —S e ttin g P oint O p e n in g
Do not attempt to align used points;
w here seriou s m isalignm ent is observed.
aligning tool if available.
2. Turn or crank the distribu tor shaft until the breaker
arm rubbing block is on the high point o f the cam
lobe. This w ill p rovide maximum point opening,
3. Loosen the contact support lock screw .
4. Use a screw d riv e r (fig. 8i) to move the point sup­
port to obtain a .019" opening fo r new points and a
.016" opening fo r used points.
5. Tighten the contact support lock screw and recheck
the point opening.
6. A fte r checking and adjusting the contact point opening
to specifications, the cam angle or dwell should be
checked with a dw ell angle m eter if such equipment
is available (see Specifications fo r p rop er dwell
angle). If the cam angle is le s s than the sp ecified
minimum, check fo r d efective or m isaligned contact
points o r worn distribu tor cam lobes. The variation
in cam angle readings between idle speed and 1750
engine rpm should not exceed 3°. E xcessive variation
in this speed range indicates w ear in the distribu tor.
NOTE: Cam angle
above 1750 engine rpm may prove unreliable
on some cam angle m eters.
Eight Cylinder Engine Distributor
On
the Vehicle
With the engine running at idle and operating tem p era ­
tu res norm alized, the dw ell is adjusted by fir s t raisin g
the window provided in the cap and insertin g a " H e x ''
type wrench into the adjusting screw head (fig. 9i).
1. P r e fe r r e d Method - Turn the adjusting screw until
the specified dw ell angle is obtained as m easured in
degrees (28° to 32°, 30° p r e fe r r e d ) by a dwell angle
m eter.
2. A ltern a te Method - Turn adjusting screw in (clo ck ­
w ise) until the engine begins to m is fir e , then turn
screw 1/2 turn in the opposite d irection (counter­
clock w ise). This w ill give the approxim ate dwell
angle required. (Use
a vaila b le.)
O f f the Vehicle
1. D istribu tor T est Method:
F ig . 9 i — A d ju s tin g D w e ll A n g le
replace them
Use an
readings taken at speeds
only when m eter is
SCREW
CHEVROLET TRUCK SERVICE MANUAL
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