The Oil Pickup screen in the engine must be checked and cleaned regularly.
Your Lycoming O-360 Operators Manual tells you to clean the screen every 100 hrs in Section 8.
http://www.vansairforce.com/community/showthread.php?p=222246
http://www.avweb.com/news/savvyaviator/savvy_aviator_57_making_metal_197700-1.html
Here are the critical bits of info:
Screen, P/N 70484
Gasket, STD-111 or AN900-16
Torque, 135 degrees rotation after full contact