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Message: [QUOTE="uga33, post: 980947, member: 386"] To the top! Was browsing the web on this subject and came across this explanation. "The explanation is that timing gears are noisey. Diesels use timing gears as they give more lifespan than chain setups used on gas engines. Gas engines have less rotational "commotion" than diesels and have good longevity with chains (usually). When you make the engine so quiet otherwise then noises that were there before but masked now can be heard. The soot in the oil gives more cushion and the lash rollover between the gears driving cam and the high pressure fuel pump is suppressed once the oil gets some particles in it. The crankshaft accelerates with each injection power stroke and slows with each compression stroke and the gears touch on one flank and then the other from the speed up and then slow down and then speed up cycling. Above idle the speed variation diminishes with increased momentum of the whole rotating mass and the noise diminishes. The break in that everyone LOVES to see happen also yields more lash between gears. Those gears had less lash when new and then the gear teeth polished over and the metal wore slightly and opened up some lash. The oil got some particles in it before the lash increased and covered the noise until you changed the oil. The wear on the gears will now be negligible for hundreds of thousands of miles. Ford may add scissor gear feature to one or two of the gears to shut it up in the future but don't count on that being a retrofit if it ever comes to be. Some 4 cylinder engines with gear drive balance shafts do this same thing after an oil service and it goes way within 500 miles on those." Anyone have any thoughts on this? [/QUOTE]