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GMC V6 and V12 Engines Engine repair and rebuilding

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  #11  
Old January 12th, 2022, 03:44 PM
James James is offline
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Default Re: Burned Valves

What is required for troubleshooting (not a complete list)(Like Ken said without seeing it we need a lot more information):
What prompt you to check the compression (rough idle)?
Did you do a compression leak down check (different than a compression check) on the cylinders to verified it was the intake valves and not the rings?
Did you check the valve clearances before disassembly?
Did you take a picture before removing the valves from the head?
Did you take a picture of the valves before cleaning?
Did you take a picture of the valve seats before cleaning?
The last time the engine was running, was there a lot of vapor coming from the crankcase breather vent?

Being it is the intake valve, was there a lot of carbon on the valve stem/head and the intake valve pocket/seat?

The way the valve look (I'm guessing here) worn in one spot, I suspect carbon on the seat had worn the valve face off. If the carbon was on the valve seats then it could help seal the valve until it broke away. Then the engine could have been running rough at idle.

What I suspect:
If there was a lot of carbon on the valve, guides are worn out (the o'ring inside the valve retainer don't stop oil vapor from entering through the valve guide, even with a shroud on the spring). With worn guide I suggest a bronze sleeve be installed (In my opinion knurling the guide is at best a temporary fix) on both intake and exhaust guides. I would also have all guides machine for positive seals.

Both heads should get the same repair work.

It look like you might have enough valve margin to grind the valve to new condition.

There is a possibility the valve job will not fix the low compression, if the rings are worn out (this is where a compression leak down test would help).
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  #12  
Old January 12th, 2022, 05:30 PM
CMCamp CMCamp is offline
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Default Re: Burned Valves

I have attached a picture of that valve before it was cleaned. Should have sent it along with the cleaned shot. Thanks for the feedback.
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File Type: jpg Burned Valve Cyl 2.jpg (2.59 MB, Multiple views, 11 clicks)
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  #13  
Old January 13th, 2022, 04:29 AM
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AZKen AZKen is offline
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Default Re: Burned Valves

"Listen son, Now that there is some bad car...I say listen son, that there is some bad carbon"
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