[Y-Blockhead]

Originally Posted by SteveR.

Just got back from a shortened drive. At idle, the engine made a sudden loud "clack", followed by severe knocking/banging. The sound eased up pretty quick, and the engine kept running. I shorted the front two plugs and it doesn't seem to make a difference. Shorting the rear two plugs causes a noticeable drop in RPM. Seems like the front two cylinders aren't firing. Is camshaft breakage common?

I'll do some more troubleshooting and pull the head soon.

Steve if the cam broke the front two would still be running and the back two would not. Also your distributor is turned by the cam. This is because the the cam is turned by the front of the cam. It also would be pretty hard to break a cam. So you can rule that out. Keep us posted to what you find.