Originally Posted By: Tegger
Originally Posted By: mechtech2
Timing chains and gears were a daily bread and butter job at shops. Esp with nylon coated gears.
You're thinking of timing GEARS. These were the really old style that had direct gearing between cam and crank. You had to coat at least one of the gears with nylon to quell the really loud whine that gears caused. Sometimes the entire tooth array on at least one gear was nylon or phenolic. The nylon frequently broke up and stripped, stranding the vehicle. These were heavy, noisy, and expensive; and, I believe, were largely displaced by chains from about the 1930s.
Most chain-driven cam-in-block American engines had an inverted-tooth chain system, also known as "silent chain". These did not need to be coated with anything; nor did they normally need replacement.
Not quite. GM and Ford (and probably other makes) used a nylon upper gear on their timing chains in their lopo smallblock engines. This started sometime in the 70's IIRC and continued on up through the early 90's.
Example: Ford 302 (lopo version, Town Car, Grand Marquis...etc) had a single roller chain with a nylon toothed upper gear. The gears can, and do fail.
The 302HO from the Mustang, Cougar, Thunderbird, LSC (and some lucky lopo's like the one in my '89 Townie) all got a double roller timing set with metal gears. They last forever.
Same story with the gear drive on the 300 I6. Early models had metal gears. They were loud (like you mentioned). Ford's attempt to quiet them was to make the teeth on at least one of the gears nylon. They would break eventually, like mine did towing a trailer down the 401. Not a pleasant experience, and that's how my F-250 ended up with a 302HO in it.