Hey guys i just put in a new crank kit and HV oil pump in my 400 because of the low oil pressure i was getting before so now i am running around 70 psi when cold and about 20-30 psi when hot i also want to add that i put in full synthetic valvoline 10w-30 after i put the new parts in was running fine for the first 2 days but this morning when i retorqued the heads and rockers when i started it after it started popping from the passenger side rear of the motor as your looking at it from the front of the truck i took the valve covers off and retorqued the rockers and checked the cylinder plug which has oil on it... now whats the most likely to cause this i also put in new valve stem seals since this cylinder had the same problem in it before? i checked compression and it went up to 140 psi and let it sit for about 10- 15 min and it only leaked about 5 psi.

 

Not sure what you mean by "POPPING" but could be the guides or seats in the head. Could also have piston slap.