Chevrolet 70 Series 1970, Service Manual

Page: 560 / 841

ENGINE ELECTRICAL 6Y-19
gask et on block, and lu b rica te d is trib u to r drive
g e a r with engine oil.
3. T urn ro to r so segm ent points to the m ark
m ade a fte r disengaging g e a rs . As d is trib u to r is
in s e rte d into place, s p ira l g ea r w ill cause ro to r
to tu rn counterclockw ise. It may be n e c e ssa ry to
in s e rt the assem bly s e v e ra l tim e s to find the c o r­
re c t position to bring ro to r segm ent to No. 1 firin g
p o sitio n . P e rfo rm Steps 3, 4, and 5 under "If
Engine Has B een C ranked" following:
IF ENGINE HAS BEEN CRANKED
1. Rem ove left-h an d valve ro c k e r a rm cover.
T urn engine o ver by in term itte n tly operating s t a r t ­
e r and observe m ovem ent of No. 1 intake valve
(second valve fro m fro nt). When intake valve s ta r ts
to c lo se (ra is e up), continue to tu rn engine slowly
until p o in ter on tim ing g ear cover is at p ro p e r
tim ing m ark on cran k sh aft pulley (fig. 2). E n­
gine is then in No. 1 firin g position.
2. In stall d istrib u to r a s d esc rib ed in Step 1
prev io u sly . It may be n e c e ss a ry to tu rn the oil
pump drive shaft to p e rm it engagem ent of drive
shaft with d istrib u to r d rive g ea r.
3. In sta ll d is trib u to r hold-down clam p and cap
sc re w .
4. In stall d istrib u to r cap. In stall sp a rk plug
w ire s in cap "in c o rre c t firin g sequence — 1 -6 -5 -
4 -3 -2 on V6 engines - - sta rtin g with No. 1 w ire
in socket adjacent to No. 1 firin g position m ark
on d is trib u to r housing, then proceeding clockw ise
around the cap.
In sta ll secondary w ire from
ignition co il in ce n te r socket in d is trib u to r cap.
Connect d istrib u to r p rim a ry w ire to negative (-)
te rm in a l on ignition coil.
5. Check and ad ju st ignition tim ing a s p re v i­
ously d ire c te d under "Ignition Tim ing."
DISTRIBUTOR CONDENSER
C ondenser, m ounted on b re a k e r p la te and con­
n ected a c ro s s the points, red u ces point a r c by its
ability to s to re up e le c tric a l energy.
REMOVAL AND INSTALLATION
1. R elea se d istrib u to r cap hold-down sc re w s,
rem ove cap, and p lace it out of the w ork a re a .
2. Remove ro to r.
3. D isconnect condenser lead w ire fro m con­
ta c t point quick-disconnect term in al.
4. Rem ove condenser attaching screw , lift
SPARK
GENERAL INFORMATION
S park plug life is governed to a la rg e extent
by op erating conditions, and plug life v a rie s a c -
condenser from b re a k e r p la te , and wipe b re a k e r
p la te clean.
5. In sta ll new condenser, using re v e rs e of the
p ro c ed u re outlined above.
TEST
Four fa c to rs affect condenser operation, and
each m ust be co n sid ered in making te s ts :
Breakdown. Breakdown is a fa ilu re of in su lat­
ing m a te ria l, causing d irec t sh o rt betw een m etallic
elem en ts of co nd en ser. T his condition p re v en ts
any condenser action.
Low Insulation R esistan ce . T his condition
p e rm its leakage which p re v en ts condenser fro m
holding its ch a rg e. A condenser with low insulation
re s is ta n c e is sa id to be weak.
High S e rie s R esistan ce . This is ex cessiv e r e ­
s is ta n c e in condenser c irc u it due to broken s tra n d s
in condenser lead o r to defective connections. T his
w ill cause burned contact points and ignition fa il­
u re upon in itial s t a r t and at high sp eeds.
C apacity. C apacity is built into a condenser
and is determ in ed by the a r e a of the m etallic e le ­
m ents, and the insulating and im pregnating m a te r­
ia ls . A condenser of in c o rre c t capacity w ill re su lt
in point pitting.
IGNITION COIL
Ignition co ils a r e mounted on top of block n e a r
fro n t of d istrib u to r (fig. 3). Ignition coil p rim a ry
te rm in a ls a r e m ark ed p o sitiv e (+) and negative (-).
W ire from d is trib u to r p rim a ry te rm in a l (black)
m u st be connected to the negative (-) te rm in a l of
coil. The light g reen feed w ire fro m s t a r t e r s o le ­
noid and the sp e c ia l re s is ta n c e w ire m ust be con­
nected to the p o sitiv e (+) te rm in a l of coil.
IGNITION COIL TEST
If th e re is any doubt a s to the condition of the
coil, it should be te s te d with conventional coil
t e s te r , following in stru ctio n s furnish ed by m anu­
fa c tu re r of testin g equipm ent. D efects indicated
by te s t a re :
1. Open p rim a ry c irc u it.
2. Open secondary c irc u it.
3. S horted tu rn s in p rim a ry o r secon dary.
4. High voltage breakdow n in secondary.
5. High re s is ta n c e in p rim a ry connections.
If any of the above conditions a r e evident, coil
m u st be re p la ced .
PLUGS
cordingly. To in s u re peak p erfo rm an c e, sp a rk
plugs should be checked, cleaned, and regapped
ev ery 5,000 m iles.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL