Chevrolet 70 Series 1970, Service Manual

Page: 526 / 841

ENGINE FUEL SYSTEM 6M-33
PLUG G A SK ET PIN SPRING DRIVE
1 R elief Valve Vent to Suction Side
2 Passage to Head of Relief Valve
- P ressu re Side
3 Passage F rom Relief Valve
- Suction Side
4 G ear Teeth Vent Cavity
5 Oil Seal Vent to Suction Side
Figure 24—Fuel Pump V a lv in g and Rotation tRight Shown)
A sp rin g loaded re lie f valve, in co rp o rated in
the pump body, n orm ally re m a in s in the closed
positio n , operating only when p re s s u r e on the out­
le t side (to secondary fuel filte r) becom es e x c e ss­
ive due to a plugged filte r o r fuel line. The valve
w ill open at a p re s s u r e of approxim ately 65 to 75
pounds p e r sq u a re inch, allowing fuel to re tu rn
through a p assag e in the body from the p re s s u r e
side to suction side of the pump. A sm all hole in
the pump body allow s fuel oil back of the re lie f
valve to bleed into the g e a r com partm ent. O ther­
w ise, the fuel might becom e trapped and p rev en t
th e valve from opening (r e fe r to fig. 24).
Two oil s e a ls a r e p re s s e d into the b o re in the
flanged side of the pump body with the sealin g lips
of s e a ls facing away fro m the fuel pump g e a rs , as
shown in figure 25. Two tapped holes in the u n d er­
sid e of pump body, between the s e a ls , fu rn ish a
m eans of attaching piping fo r draining off any leak ­
age. If leakage exceeds one drop p e r m inute, the
s e a ls m ust be re p la ced . The fuel pump should
m aintain a fuel p r e s s u r e a t the fuel inlet p assa g e
of 50 to 70 p s i a t 1800 rp m engine speed. L ift on
the suction sid e of pump should not exceed 48 inches.
F uel pum ps a r e furnish ed in le ft- o r rig h t-
hand ro tatio n according to the engine m odel, and
a r e stam ped "L.H. IN” and "R.H. IN .” These
pum ps a r e not interchangeable, n o r can a pump
m ade fo r one ro tatio n be reb u ilt fo r the o th er r o ­
tatio n.
NOTE: The fuel pump u sed on the 6V-53 engine
is R.H. ro tatio n and is mounted on the flywheel
housing; it is driv en by the a c c e s s o ry drive g ea r.
The fuel pump used on the 6-71 engine is rig h t-
hand rotation and driven by low er r e a r blow er
ro to r. The fuel pump used on the 8V-71 engine is
a left-h and rotatin g pump and is driven by the
rig h t fro n t blow er ro to r.
TESTING FUEL PUMP
If engine op eratio n ind icates insufficient sup­
ply of fuel to the in je c to rs and the fuel level is not
low in the supply tank, check the fuel flow between
the re s tr ic te d fittin g in the fuel re tu rn p assa g e in
the cylinder head and the fuel supply tank.
Checking Fuel Flow
1. D isconnect the fuel re tu rn line fro m the
fitting a t the fuel tank and hold the open end of the
line in a convenient re c e p ta c le .
2. S ta rt and run the engine a t 1200 rp m (no
load) and m easu re th e fuel flow re tu rn fo r a p erio d
of one m inute.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL