They(the upper/cam gears) have always been "metal", either steel, or aluminuminum. The aluminuminum gears have a nylon coating on the teeth sections that will eventually break, and fall off, causing all kinds of problems, including stopping up the oil pick-up screen. These gears are sometimes referred to as "nylon" gears, but they are not made of nylon...just the teeth are nylon coated. They did this supposedly to make the gears quieter.
Best to
always replace with a steel gear, and preferably a full roller gear
set, as a roller set will last much longer, and keep the timing more accurate over the life of the gears.
btw...I'm not sure
when they first started using the nylon coated gears, but most assuredly the '80s cars had them. My '74 had steel a gear from the factory. I replaced it with a roller in '98.
Adams' Apple2010-07-12 09:50:53______________
Joel Adams
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