I guess another opinion won't sink the boat; but I feel confidant that the "rattle" valve plug was intended, with the advent of the application of hydraulic lifters (first example FE's were mechanical), as a simple execution to allow air which inevitably will have accumulated in the main gallery and below down to the oil pump when the engine is not operating, to be purged more quickly, rather than having to push it though the clearance restrictions about the valvetrain, this in order that the system might be "charged" with pressurized oil fluid more quickly in order to better maintain silence on start-up.
Later, this was deemed unnecessary and was eliminated (cost cutting, probably saved maybe five cents on each plug; but that times how many engines?
), and I would doubt drain-backs had anything to do with it as this process would be labeled as unreliable; and as far as oil delivery to the timing gear, this is mostly handled by the high pressure oil ejected out of the clearance area of both the first main and cam bearings. And I'd probably pass on the plan of drilling a hole in the main gallery plug for greater oil volumes for the T.C. set, as it isn't needed, and isn't it the FE guy's that are restricting oil delivery to the upper valvetrain (where it might actually do some good
) for greater supplies thought to be needed for the bottom-end? And also you do know that excessive fluid volume needing to be displaced at the chain to gear or gear to gear junctures can be counter productive in high-speed applications.
Scott.
