Impreza WRX F4-2.0L DOHC Turbo (2004)
6) Ensure camshaft and crankshaft sprockets are positioned properly.
CAUTION:
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Intake and exhaust camshafts for this DOHC engine can be independently rotated with the timing belts removed. As can be seen from
the figure, if the intake and exhaust valves are lifted simultaneously, their heads will interfere with each other, resulting in bent valves.
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When the timing belts are not installed, four camshafts are held at the "zero-lift" position, where all cams on camshafts do not push the
intake and exhaust valves down. (Under this condition, all valves remain uplifted.)
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When the camshafts are rotated to install the timing belts, #2 intake and #4 exhaust cam of left-hand camshafts are held to push their
corresponding valves down. (Under this condition, these valves are held lifted.) Right-side camshafts are held so that their cams do not
push valves down.
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Left-hand camshafts must be rotated from the "zero-lift" position to the position where the timing belt is to be installed at as small an
angle as possible, in order to prevent mutual interference of intake and exhaust valve heads.
