1977 l48 4 speed with 85k original miles

Ok, after setting the timing at 3,500 rpms the engine starting making a strange noise like the a/c compressor clutch needed to be oil, then it developed into a "rattling" sound like a valve dropped and then started knocking (all of this in just a matter of minutes).

I checked compression and didn't see anything unusual. Pulled the valve covers and found a very loose push rod on #6. Pulled the intake manifold to inspect the lifters and found the lifter seemed to be stuck, so I thought I had found the problem. Changed out all the lifters, put it back together, and it actually seems to be worse.

I can't tell where the knocking is coming from: Checked compression again and this is what I have:
#1 - 160 psi #2-155 psi
#3 - 150 psi #4 -155 psi
#5 - 155 psi #6 - 155 psi
#7 - 150 psi #8 - 160 psi

Just not sure where to go next..... I did take off all the belts and crank the engine just to be sure it wasn't from something belt driven, no difference. Oil pressure is 40 psi.

Thanks in advance for any suggestions...

 

Possible wiped cam lobe(s) ... particularly at stuck lifter(s).

pull out lifter & inspect lifter face & cam lobe.

Possible collapsed lifter.

a vacuum gage in knowledgable hands can help diagnose wiped lobe and/or collapsed lifter ... a cheap essential tool.

 

get a long wood rod like a broom stick.put it on the motor where you think its making noise.i would start with the fuel pump.

 

http://www.secondchancegarage.com/public/186.cfm

 

I think you're talking about a SB but on two separate occasions my BB suddenly developed a horrendous knock. The first time I tore it down, expected the worse, but found nothing wrong. Put it back together, sounded fine. Many months later, same thing again. This time I just took it out and ran the pee out of it. Ran great, knock stopped. Never happened again. Always suspected valve train as culprit. Still a source of wonderment.

 

Make sure the timing is not to far advanced, Then pull one spark plug wire at a time to see if there is any change in the noise

 

Could it be that when you changed the timing it is now too far advanced?