Hello Again, I have a 66 coupe with a recently rebuilt '68 302, probably has around 100 miles on it, ran hot a couple times to the point of coolant boiling out of reservoir, new Champion radiator fixed that problem, but now it has a knocking sound during warmup. If I pull the #5 plug wire the noise goes away. If it's fairly dark out, when I pull the #5 plug wire I can see a spark at the coil boot. I looked in the #5 combustion chamber with a scope and the top of the piston is shiny, like oil. I did a differential pressure test on #5 at 80 PSI and it held at about 72 PSI. Did a test on #6 and same result. During the pressure test, no bubbles were noted in the radiator, no air from PCV, no air from filler cap hole. I don't think it's piston slap because the block was machined and bored .030 over. Any ideas where the oil could be coming from, or what the noise could be? Thanks -Jeff