Engine Noise From #5 Cylinder '68 302

[Jeff Massey]

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

 

[horse sence]

Broken valve spring could make the noise. Bent push rod ,but if the sound goes away when you pull the plug wire it has to be something with the piston or rod .
Oil could be coming from a few places .The valve stem cup ,Rings not lined up properly when installed on the piston .Sucking oil at the intake and head at intake port if gasket didn't seal properly .PCV valve stuck open .But with the knocking i would believe it is in the piston area ,probably with the rings . What pistons did you use ,it doesnt take a lot to damage a cast piston ,especially if it got hot .

 

[Jeff Massey]

Broken valve spring could make the noise. Bent push rod ,but if the sound goes away when you pull the plug wire it has to be something with the piston or rod .
Oil could be coming from a few places .The valve stem cup ,Rings not lined up properly when installed on the piston .Sucking oil at the intake and head at intake port if gasket didn't seal properly .PCV valve stuck open .But with the knocking i would believe it is in the piston area ,probably with the rings . What pistons did you use ,it doesnt take a lot to damage a cast piston ,especially if it got hot .

Thank you for reply, I can always count on horse sence! The Pistons were purchased by the machine shop, and I'm quite sure they were Sealed Power. They bought all the parts, cam, bearings, pistons, rings, oil pump etc, and I did all the assembly...my first V8 build, but I was very meticulous on every step, even spacing the ring gaps, but the engine did sit for about 3 years before I fired it up, furthermore if it matters the heads I had machined with the block somehow developed a crack at the rear freeze plug so I replaced them with a set of 68 heads (because of the particular combustion chamber size) but these heads were stamped 2V rather than 4V...also I did pull the push rods from #5 a they were straight. I did not inspect the valve springs

 

[Jeff Massey]

but since it goes away within a minute, I'm feeling like it can't be causing any major damage...do you agree? At least Im thinking it can wait for a winter investigation, bout the same time I send off my steering gear box for a rebuild...got about 6 inches of play in the wheel!