Isuzu Trooper II 1986 Manual page 20

under TIMING BELT & SPROCKETS. On 1.9L models, align mark on camshaft
with mark on No. 1 rocker arm shaft bracket. Align notch on
crankshaft pulley with "O" mark on front cover. When 2 sets of marks
are aligned, No. 4 piston is at TDC of compression stroke.
2) Ensure that marks on oil pump inner and outer rotors are
aligned. Engage oil pump drive gear with pinion gear on crankshaft.
Ensure that alignment mark is facing to the rear and approximately 20
degrees in a clockwise direction away from crankshaft. See Fig. 12.
3) Ensure that mark on drive gear is facing rear of engine
with oil pump installed. Slot at end of drive shaft must be parallel
with front face of cylinder block, and offset forward. See Fig. 12.
4) Install pump cover by fitting it to dowel pins, then
install mounting bolts. Install relief valve assembly and oil pipe
rubber hose. Reverse removal procedure to complete installation.
Fig. 12: Installing Oil Pump on 1.9L Models
Courtesy of Isuzu Motor Co.