Subaru 2009 IMPREZA Service Manual page 273

Cam Sprocket
MECHANICAL
C: INSPECTION
1) Check the cam sprocket teeth for abnormal wear
and scratches.
2) Make sure there is no free play between cam
sprocket and key.
3) Check the cam sprocket protrusion used for sen-
sor for damage and contamination of foreign matter.
ME(H4SO)-55