How to replace timing chain on 2003 gmc envoy?

You can replace the timing chain, but its very time consuming procedure:---

This is over a 16 hour job for someone with experience of this vehicle

may be over 20 hours for 1st time.

The details are as follows :---

Drain the engine coolant.
Remove the cooling fan and the shroud.
Remove the drivebelt.
Remove the water pump.
Remove the crankshaft balancer.
Remove the power steering pump.
Raise the vehicle.
Remove the oil pan.
Lower the vehicle.
Remove the 7 mm center bolt
Loosen and remove the remaining engine front cover bolts.
Place two of the front cover bolts in the jack screw holes on the front cover and tighten the bolts evenly to release the front cover from the engine.
Remove the two bolts from the front cover.
Remove the oil pump.
Remove the front cover.
Follow procedures for Timing Chain in the link below.Just click the link below:---

http://ww2.justanswer.com/uploads/molurch/2011-09-05_004046_tc.pdf

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That will help.---------