Some cams can have chrome plating that rubs off or if the metal just wears down over time. Here is a link with pictures of bad cams but it is for AIRPLANES. http://www.sacskyranch.com/camshaft.htm
The theory is the same plus there is pictures on this page.

I decline to go into oil weight and additives. I will just say change the oil every few months and keep it to the proper level.

Dear Joe H. I cant hear the lifters because I have an exhaust leak. I will take your advice and put good gas back in it. Thanks Bud.

250 Integrated Head / 1981 C-10 Pick up.