Griff in Fairbanks wrote:
IIRC, OEM sprockets were a composite material and OEM chain was an 'economy' version. Replaced with metal sprockets and premium chain. Lasted at least 150,000 miles that I know of.
GM did the same thing. That composite around the timing chain gear was meant dampen it and make it run quieter. Problem was, once you had some miles on (as you noted) the stuff could fail at any time with no warning. I've seen big chunks of it break off, leaving so much slop in the chain that it was useless. My fix was to buy a high performance all steel double roller timing set. TRW, I think it was. Yeah, it was a small bit noisier, but the timing chain never failed again. It was like a permanent fix. :)
