My '68 327 (nearly bone stock) has a hard rapping sound that seems to come in at about 2500 RPM and above. Below that it is fine. This is a freshly rebuilt engine, and the problem happenned after about 20? miles of driving.
I removed all spark plugs one at a time, trying to find the cylinder making the noise, but there was no change in the noise with any plug, so I doubt it is a bearing. Plus I took off the pan, and saw no signs of problems in the bottom end. I replaced the lifters, thinking they were broken, and the problem was not solved.
Anyone have any ideas as to what is wrong with my engine? I am going to do a compresion test and buy a stethoscope tonight. Thanks for your help.