"Valve train noises occur at half of crankshaft speed so even if your ear can't tell whether the noise is happening at 700 rpm (raps per minute) or only 350 rpm, your eyes can. Hook the timing light to any one cylinder and watch the flash illuminate the timing mark. Stare at it for a while and see if the flash jives with the knock. If it does, then it is more likely to be rocker arms, pushrods, lifters, camshaft, cam bearings, timing chain and gears. If the noise seems twice as fast it is probably in the crank, mains, rods, rod bearings, wristpins and pistons."