I've seen them fail and when the chain jumps, it bends valves; my recommendation is you don't put it off too long. The problem occurs because the tooling that was used to stamp the chain links wore and created sharp edges, which cut through the plastic tensioner faces. The amount of wear on the tooling, if any, when the links were stamped varies so that is why some engines don't experience the problem, some fail with little mileage (under 50,000 miles) and some can go well over 100,000 miles until the problem occurs. As the chain cuts into the plastic tensioner face, it will start to whine. Eventually, the chain will begin to ride directly across the hardened steel plunger of the tensioner, which can then lead to potentially causing the timing chain to jump and serious damage occurs. To do the "basic repair" as outlined in the TSB, one is usually looking in the $1200-$1600 range, depending on the shop's labor rate. Many will opt to add to the basic repair while everything is exposed, which increases the cost. This can include replacing the primary chain and tensioner, guides, water pump, thermostat, serpentine tensioner and belt. Those who want to eliminate another potential problem, which can cause low oil pressure issues, may address the rear timing cover, which can develop a leak at the cover plate gaskets at the back side of the rear timing cover.
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