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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old January 11th, 2022, 03:30 PM
CMCamp CMCamp is offline
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Default Burned Valves

My 1962 K1001 failed a compression test pretty miserably. It has a 305D V6 and here are the readings Cyl 1 = 125, Cyl 2 = 47, Cyl 3 = 135, Cyl 4 = 47, Cyl 5 = 130, Cyl 6 = 100. The heads are off now and it is pretty obvious that I have two burned inlet (yes inlet) valves in 2 and 4 plus damage starting in 6. I'd like to get your opinion on what might have caused this. Several coincidences here: all inlet valves, all on the passenger side head, all damage at the point where the valve edge is closest to the spark plug.

The heads are off now and disassembled. I cleaned the bad valves and the damage is pretty obvious. I attached a picture, but the lighting is not good.

What else should I be checking to possibly prevent this damage in the future. Appreciate your help.
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File Type: jpg Burned Valve.jpg (2.60 MB, Multiple views, 15 clicks)
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  #2  
Old January 11th, 2022, 03:52 PM
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Default Re: Burned Valves

I don't know anything, but wouldn't a burned intake valve mean you're getting early ignition? I'd look at timing and pinging. If the timing is fine you may need to run a higher octane fuel. That's just a guess based on the logic of how intake and exhaust valves work.
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Old January 11th, 2022, 06:44 PM
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Default Re: Burned Valves

I don't see a burnt valve. Describe where you see a burnt valve in that pic. Low compression on one head is usually a blown head gasket....or a crack. Something wrong with the valve train on that side. Broken springs, etc. etc. Maybe even timing.

Just to repeat, I don't see any "damage".

Last edited by AZKen; January 11th, 2022 at 07:06 PM.
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  #4  
Old January 11th, 2022, 08:48 PM
Prowbar Prowbar is offline
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Default Re: Burned Valves

Quote:
Originally Posted by AZKen View Post
I don't see a burnt valve. Describe where you see a burnt valve in that pic. Low compression on one head is usually a blown head gasket....or a crack. Something wrong with the valve train on that side. Broken springs, etc. etc. Maybe even timing.

Just to repeat, I don't see any "damage".
Take a look at the circled area Ken.
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File Type: jpg valve damage.JPG (93.3 KB, Multiple views, 14 clicks)
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  #5  
Old January 11th, 2022, 10:13 PM
CMCamp CMCamp is offline
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Default Re: Burned Valves

Prowbar has circled the exact area of the damage. I apologize for the bad camera work. In the right light it looks pretty bad. I was hoping to find a blown gasket, but it looked fine.
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Old January 11th, 2022, 10:21 PM
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Default Re: Burned Valves

Not definitive enough. The extra low pressure in multiple cylinders, on same bank, just doesn't feel right. Together with sketchy pic of alleged burnt valves. The pics below are actual burnt valves. You can see a clear compression leak path. I will leave the analysis up to you, other members and the OP. This is all I can offer from one pic and test results. Just something to consider.

In the pic, all I see is possible pitted seat, normal. Depending on mileage. Don't think that causes 47 PSI. Need to see the gasket and if there are witness trails on the head......or better pics of all the valves showing definite seat lip failure as in: "burnt valves"

It is the nature of troubleshooting from afar and it is necessary not to take the ideas of the poster as to what is wrong. I must go by what I see and read. I don't see the gasket, I don't see a burnt valve. I didn't see the compression test. If I trusted a OP without seeing or testing, I would never find the issue. I would just be following them around in a circle. If it seems stubborn, it is. Don't mind being wrong but I don't give up until I see proof. Otherwise what good would I be as a yes man?

Of course, the poster being right there examining parts, can be completely correct in their analysis....but they did ask for comment.

If I saw a burnt valve I would say obviously it's cased by excess heat. Improper cooling or valve train failures I've already mentioned.
Attached Images
File Type: jpg burnt valve3.jpg (39.8 KB, Multiple views, 5 clicks)
File Type: jpg burnt valve2.jpg (5.37 MB, Multiple views, 4 clicks)
File Type: jpg burnt valve.jpg (96.1 KB, Multiple views, 4 clicks)

Last edited by AZKen; January 11th, 2022 at 11:00 PM.
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Old January 12th, 2022, 06:00 AM
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Default Re: Burned Valves

Yeah Ken I didn't see it in the second picture either but my eyes aren't what they used to be. If you click on the first from CMCamp then click it again it'll blow up to super magnified. It looks like (and again we're looking through a straw here) but it looks like he had a pretty good burn but when he cleaned it up he cleaned off all the burn. With it being shiny it's tough to see, but the lip on the valve is definitely pitted and maybe even chipped along the edge.
Because it's so shiny and clean (good job CMCamp!) you can't see anything through the shine unless you blow it up. Next time I'd probably take the pic while it's still dirty and marked up.
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Old January 12th, 2022, 09:00 AM
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Default Re: Burned Valves

Fetch, we are buddies, so this is not at you.

To whom it may concern

I did blow up the first pic before I commented. The second pic is just the first pic..... rotated, No clarification by rotating a pic. I don't need to be convinced of anything. It's my opinion until, if, and when, there is more info. No big deal here. If I'm wrong I will be last to admit it.
Thru my eyes, thru the computer, thru the glare, thru the shine, with the angle, with rotating, with zooming, I don't see a burnt valve.
I do see, on one part of the valve, the face of Homer Simpson.

Last edited by AZKen; January 12th, 2022 at 09:32 AM.
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Old January 12th, 2022, 02:02 PM
Prowbar Prowbar is offline
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Default Re: Burned Valves

Quote:
Originally Posted by AZKen View Post
Fetch, we are buddies, so this is not at you.

To whom it may concern

I did blow up the first pic before I commented. The second pic is just the first pic..... rotated, No clarification by rotating a pic. I don't need to be convinced of anything. It's my opinion until, if, and when, there is more info. No big deal here. If I'm wrong I will be last to admit it.
Thru my eyes, thru the computer, thru the glare, thru the shine, with the angle, with rotating, with zooming, I don't see a burnt valve.
I do see, on one part of the valve, the face of Homer Simpson.
OK Ken your point is clear
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Old January 12th, 2022, 02:25 PM
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FetchMeAPepsi FetchMeAPepsi is offline
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Default Re: Burned Valves

Quote:
Originally Posted by AZKen View Post
Fetch, we are buddies, so this is not at you.

To whom it may concern

I did blow up the first pic before I commented. The second pic is just the first pic..... rotated, No clarification by rotating a pic. I don't need to be convinced of anything. It's my opinion until, if, and when, there is more info. No big deal here. If I'm wrong I will be last to admit it.
Thru my eyes, thru the computer, thru the glare, thru the shine, with the angle, with rotating, with zooming, I don't see a burnt valve.
I do see, on one part of the valve, the face of Homer Simpson.

We're always buds!

And there's the trouble! Homer Simpson should definitely NOT be working on your V6! He repairs everything with a hammer, including his nuclear reactor. I bet he chipped it while "fixing" it after a few rounds of Duff beer with the boys
I recommend a trail of donuts from the motor to the nearest pub to solve the problem, and still checking the timing for preignition.
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