Bolt on timing chain tensioner
I have had a tensioner fail and chunks of plastic get between the chain and gear shearing the pins holding the links together
If a nylon chunk can shear a chain pin...! I got a 200,000 mile plus Mazda that has 2 6 inch long slippers and a 1" shoe that contacts the roller style chain and it has barely any wear on it, as well as all modern engines
I have had 3 engines of my own that lost timing chains and one of my family's
The first was a 67 289 Ford with 160,000 miles on it. The nylon teeth on the cam sprocket desintargrate, needless to say I had canted valves and pigtail pushrods
The next was a 2.0 85 chevy I4, timing chain slipped / broke, just don't remember why, 250,000 miles
Then a 92 3.1 Chevy V6, this one had all the timing chain plates split at the pin of one link. This one the tensioner was a mess with big chunks scattered all over the place. 160,000 miles
The family one was on a fiero don't know the reason but it turned out to
not be a clearance engine! Unknown miles.
All of the engines were propperly maintained,
The common denominator was nylon inside in engine for at minimum 2 most likely 3 of the engines