Re: Knock when cold! 2008 2.3
Things that knock when cold are generally parts that get hotter than other parts. Meaning, in the past, pistons were subject to 'slap', which made a knocking sound, when cold, that went away when they got hot. The pistons were subject to 'collapse', caused by ???, I dunno. As the piston moved up in the bore, it was/is pushed more to one side of the bore by the connecting rod, and when the cylinder fires, the pressure is on the other side of the piston, against the other side of the bore. As the engine heats up, the piston expands(aluminum) more than the iron cylinder, and closes the gap, leading to less noise.
Other than that, it could be end play in a cam shaft, cam shaft follower, or a valve moving in its guide(not common to be noisy). Cam noises should be at 1/2 crankshaft noises. If you can figure the timing of the noise compared to crank speed, you may determine w/o further exam if it is crank or cam related. Using a timing light to flash and show 'cam' speed may enable you to determine if it is crank or cam speed as it triggers your mind to match the sound occurrence to the flicker occurrence of the timing light.
tom
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