the dealer i bought my car from told me the last owner put a bigger cam in the 305. i noticed that the there is a chattering noise coming from under the vavle covers. could the rockers be loose or could the rods stretched? should i readjust the vavles?

 

The first thing to do is check the oil level and pressure. If that's all in order, remove the rocker cover on the noisy side, check the height of all the rocker studs to verify that you don't have one or more pulling out and/or bent, inspect the springs for breakage, and spin the push rods with your fingers to check for bending. You may have to rotate the engine by have a couple revolutions to position all the rockers/valves so that you can perform these inspections on each valve.

Once you have determined that there is no mechanical damage, you can adjust the lash of each rocker. Search the archives for complete directions. I know that there have been volumes posted on the topic more than once.

 

might be preignition too and not a problem with the valves. if after doign what mr. vader said and your problem continues check the timing, look at the knock counts, and increase the octane

 

is there a tool to count the knock counts?