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So my 02 sierra 5.3 w 275k miles developed a severe knock and when i started investigating found the #8 cylinder had 0 compression... instead of trying figure it out i thout swapping in an engine w less miles would be easier...

I found a 2000 5.3 at you u pull it junk yard and pulled it out and got it home and all the way installed but as i was filling the oil found some metal in the oil pan and when i took off the oil pan the 7 and 8 cylinders were blown apart and chunks of the pistons had flown around in the motor... So it was clear that engine probably couldn't even be rebuilt.

Next I found an 05 parts truck and pd 950 for it with the 4.8. pulled the motor and started prepping for installation. I was trying to remove one of the broken exhaust manifold bolts and drilled too far and drilled into the head at the intake for the #8 cylinder... I'm guessing that will not be fixable. And im thinking i use one of the heads from the other 2 motors i have sitting in the garage. The heads are mostly identical for all 3 motors. The 02 is stamped 862 and both the 2000 and 05 heads are stamped 706. Only difference i can see is the 05 pcv valve is different but that is on the other head. So can i use one of the heads from the other motors? Im thinking the you pull it one will be my best bet because the 02 had 0 compression and the exhaust valve on the #8 cylinder does not seat properly. To remove the head do i meed to remove the rocker arms push rods and springs? I can't just unbolt the head? I know i will need new gasket and bolts and if i remove the rocker arms and pushrods they need to go back in the places they came out of does anyone have advice or recommendations? Im considering taking it to a shop to have it done anyone know what that might cost?

Also is it ok to change only one of them?

One more small question about the swap... The 02 has the manual accelerator and the 05 has the one controlled by pcm. I was going to use the intake manifold from the 02 and keep the manual accelerator so i don't need to switch out more parts will that work?

Also is it worth putting the dual cooling fan into the 02 or should i stick with thw older manual one?
 

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So my 02 sierra 5.3 w 275k miles developed a severe knock and when i started investigating found the #8 cylinder had 0 compression... instead of trying figure it out i thout swapping in an engine w less miles would be easier...

I found a 2000 5.3 at you u pull it junk yard and pulled it out and got it home and all the way installed but as i was filling the oil found some metal in the oil pan and when i took off the oil pan the 7 and 8 cylinders were blown apart and chunks of the pistons had flown around in the motor... So it was clear that engine probably couldn't even be rebuilt.

Next I found an 05 parts truck and pd 950 for it with the 4.8. pulled the motor and started prepping for installation. I was trying to remove one of the broken exhaust manifold bolts and drilled too far and drilled into the head at the intake for the #8 cylinder... I'm guessing that will not be fixable. And im thinking i use one of the heads from the other 2 motors i have sitting in the garage. The heads are mostly identical for all 3 motors. The 02 is stamped 862 and both the 2000 and 05 heads are stamped 706. Only difference i can see is the 05 pcv valve is different but that is on the other head. So can i use one of the heads from the other motors? Im thinking the you pull it one will be my best bet because the 02 had 0 compression and the exhaust valve on the #8 cylinder does not seat properly. To remove the head do i meed to remove the rocker arms push rods and springs? I can't just unbolt the head? I know i will need new gasket and bolts and if i remove the rocker arms and pushrods they need to go back in the places they came out of does anyone have advice or recommendations? Im considering taking it to a shop to have it done anyone know what that might cost?

Also is it ok to change only one of them?

One more small question about the swap... The 02 has the manual accelerator and the 05 has the one controlled by pcm. I was going to use the intake manifold from the 02 and keep the manual accelerator so i don't need to switch out more parts will that work?

Also is it worth putting the dual cooling fan into the 02 or should i stick with thw older manual one?
Take the good bottom end, put 2 good 706 heads on it with all your original accessories, intake, etc, and be done with it. To remove the heads, you don't need to remove the springs, just the rockers and head bolts. Keep your mechanical fan as well.
 

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Just pack the exhaust manifold bolt hole full of JB weld and use a doorman repair bracket. Think I’m joking, I ran a 150 shot, cam, 4K stall, and beat on mine for years without a hiccup.

LS heads are also universal, meaning there’s no left or right side. And 706 and 862s are the same head, just cast at different locations. 706s were prone to cracking, 862s are bullet proof. But both are the same. You can put one 706 and one 862 if you want, meaning only swap one head. Iv seen many LKQ and parts store reman come like that out the door.
 

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What he said. You got 3 engines, so just pick what’s not broke and make one good one and run it.
 
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