GMC 1989 Light Duty Truck, Repair Manual, Page: 9 / 998

GENERAL INFORMATION OA-3
L6 ENGINE
4. E n g in e I.D. (O p tio n a l L o c a tio n )
5. E n g in e C ase Pad
6. E n g in e I.D.
1. E n g in e I.D. —
2. D is trib u to r Pad
3. E n g in e I.D (O p tio n a l L o c a tio n )
V8 ENGINES-GAS
9. E n g in e I.D
V6 ENGINE
V8 ENGINES-DIESEL
F
-00527
Figure 5— 4.3L V6 and all V8 Engine I.D. Locations
N O TIC E: M o s t m e tric faste n e rs have a b lu e
c o lo r coating. H ow ever, this should n o t be used
as p ositive id e n tific a tio n as som e fasteners are
n o t c o lo r co ated .
G e n e ra l M otors E n g in e e rin g S tan d ard s , alo ng with
other North A m eric an Industries, have adopted a portion
of the standard m etric fas ten er sizes d efined by IS O
(International S tan d ard s O rg an izatio n ). T his w as d on e to
reduce the n um ber of fas ten er sizes used and yet retain
th e b est strength q u a lities in ea ch th rea d size. For
e x a m p le , th e cu sto m a ry 1/4-20 and 1/4-28 screw s are
replaced by the metric M 6 .0 x 1 screw w hich has nearly
the sa m e d ia m e te r and has 25.4 th rea d s per inch. T h e
th read pitch is in b etw een the cu stom ary co arse and fine
th read pitches.
M etric and cu stom ary thread notation differ slightly. T h e
d ifferen ce is shown in figure 14.
FASTENER STRENGTH
IDENTIFICATION
M ost co m m on ly used metric fas ten er strength properly
classes are 9.8 and 10.9 with the class identification
em bo ssed on the head of each bolt. C u sto m a ry (inch)
strength classes rang e from g rad e 2 to 8 with radial line
identification em bo ssed on each bolt h ead . M arkin g s
correspond to two lines less than th e actual g rad e (i.e.
g rad e 7 bolt will exhibit 5 em bossed radial lines on th e
bolt head). S o m e m etric nuts will be m arked with single
digit strength identification num bers on the nut face.
Figure 6 shows the different strength m arkings.
W h e n replacing m etric fasteners, be careful to use bolts
and nuts of the sa m e strength or g rea ter than th e original
fasten ers (the sa m e n um ber m arking or higher). It is
likewise im portant to select re p la cem en t fasten ers of the
correct size. Correct re p la cem en t bolts m etric fasten ers
availab le in the afterm arket parts ch an n els w ere desig ned
to m etric stand ards of countries other than th e United
States, and m ay be of a lower strength, m ay not have the
n u m b e re d h ead m a rk in g sy ste m , an d m a y be of a
different th read pitch. T h e metric fasten ers used on G M
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