Stovebolts in cars ran a fiber gear (Bakelite) back as far as the early 1950s, at least. Trucks ran an aluminum gear. The plastic coated timing chain sprockets (not gears) were used in other engines during the 1960s. Those were notorious for the plastic getting brittle and breaking up- - - -and the debris would clog up oil pump pickup screens and cause low or no oil pressure.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!