Many modern automakers are switching to timing belts in place of timing chains, to help reduce weight and reduce initial build costs. There are, however, a few drawbacks to a timing belt. The big one is that these belts are rubber and need replacement every 60,000 to 100,000 miles. If one should happen to break on an interference engine -- one where the valves travel into the stroke of the piston -- it can result in catastrophic engine failure. Fortunately, your 2002 Blazer does not suffer from the drawbacks of having a timing belt.
The 2002 Blazer's 4.3-liter engine uses a timing chain, not a timing belt. The manufacturer does not recommend any maintenance procedures on this chain.
