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Chains gone = Chains buggered. Stretched and setting off the engine light because the cams are out of phase.
Actually the 04 vz were fine as were some of the 05 vz the problem occurred after engine number H053340001 according to the holden service bulletin and there have been reports of this issue even in the sidi engines that holden have repaired under warranty so unless people are lying i'm gunna say it wasn't fixed even though the same service bulletin reports that it was fixed from engine number H071380576 build date 18/05/07The whole issue is a hangover of the VZ '04, '05, & '06 and the very first VE's. 15 fricken years ago! It was fixed, the buggered ones have mostly been fixed or are not on the road.
All timing chains stretch and that is a fact of life. The old V6's had a short but reasonably heavy duty chain and they stretched but with the use of a tensioner (which do fail) were not considered a wearing item and therefore considered serviceable for the life of the motor. These modern overhead cammed motors use a lighter chain but much longer so therefore a small amount of wear/stretch over a much longer chain gives the impression the chain has stretched much more but in reality the wear/stretch per link is the same. Unfortunately with the overhead cam configuration cam chains are now a wearing item and one that will need replacement if you want to maintain good performance. This issue isn't reserved to GM.
All timing chains stretch and that is a fact of life. The old V6's had a short but reasonably heavy duty chain and they stretched but with the use of a tensioner (which do fail) were not considered a wearing item and therefore considered serviceable for the life of the motor. These modern overhead cammed motors use a lighter chain but much longer so therefore a small amount of wear/stretch over a much longer chain gives the impression the chain has stretched much more but in reality the wear/stretch per link is the same. Unfortunately with the overhead cam configuration cam chains are now a wearing item and one that will need replacement if you want to maintain good performance. This issue isn't reserved to GM.