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Hi, my name is Tim, and I am new to the forum and my '05 Colorado with the 3.5. On the way home from purchasing it, it kicked the PO302 code, so I read up on it and completed a compression test and leak down test. The compression test showed two cylinders were 10% low, and the leakdown test verified that those two holes had significantly more leak into the manifold. The truck has a slight hiccup in the idle but not other noticeable issues. This leaves me with several questions:

1- How long with the truck run reliably like this?

2- Is the problem typically with the intake valve seats or guides? The guides appear to be threaded-could I change them without pulling the head if I follow the procedure outlined by GM for changing the springs in the early bulletins? (Assuming I have the mechanical aptitude.)

3- Are there any casting marks to tell which heads have the updated (from GM) seats and guides? I would love to just find a junkyard head that is updated, but I can't figure out how to tell.

4- Are there any updated heads that went on the '06s? Is there a VIN number breakpoint that would tell me which 06 heads would be worth swapping out?

I have spent a number of hours reading posts-this is a great forum. If this information is out there and I have been searching in the wrong place, please point me in that direction. I know this dead horse has been beaten a good bit, but I appreciate any help and feedback you can give. I really like this truck, but I hate to spend more on a GM reconned head than it's worth!!
 

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The only problem with the early heads were the substandard valve guides and there is no problem with the valve seats. There is no visual clue to tell if the valve guides have ever been replaced. The valve guides are pressed in and cannot be changed with the head installed but even if they could the valves will still leak until a valve job is done. New valve guides are inexpensive and a typical machine shop charge for an I5 valve job with new guides and valve seals should be about $325.00. The sub-standard valve guides were used until some time in the '08 production run. Your head can easily be repaired (better than new) with a valve job & new aftermarket guides and seals. There is no way to repair it with the head on.
The GM reconditioned head costs something over $1,000. exchange and is nothing more than someone else's used head with a valve job. To me that is just rewarding GM with another $600. profit to fix a problem they created in the first place. So do you want to pay $1,000. + or $325. for your valve job? The dealer will give you neither a thank
you or a kiss for your present.
If you just bought the truck was there any warrantee?
 
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