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Hard miss on cyl 7 - stuck valve

VortecMAXi

By VortecMAXi
in Ask A GM Technician

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VortecMAXi New Member

VortecMAXi

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Posted

Hi Guys,

 

I own a 2007 silverado w/ a 6.0L vortecmax

 

I am experiencing a hard miss on cyl 7.

 

Opened the valve cover and discovered one valve is stuck down (won't pop back up). The spring assembly appears to be intact. Push rod appears to be functioning with the rocker arm ok.

 

What is the best way to tackle this issue?

 

Thanks in advance!

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

What causes this symptom? What will the machine shop do?

 

If the spring is not broken then something is causing the valve to stay open. Can you manually pull the valve up? Can you make the valve move at all? If the spring is not broken or collapsed, then the valve is either bent, or there is something mechanically holding the valve open. There could be something between the valve and valve seat, could be seized in the valve guide, or valve is bent. If the spring is broken, and you can pull the valve up by hand, you can change the spring with the head on the engine. I would try to rotate the valve to see if it can rotate freely, and can rotate freely in the closed position as well. To change spring with the head in place, take spark plug out, rotate engine to put that cylinder at BDC at end of power stroke, put adaptor into spark plug hole, connect air line to it. Use a valve spring compressor tool to compress the spring and remove keepers and retainer. Change spring and put it back together.

 

If spring is not broken, take the head off, flip it over and see if you can find a reason for the valve to be open. This is where you will end up sending head to machine shop for repair of bent valve or something jammed into the seat. You will also need to find out what happened. Change the timing chain recently? Is the top of the piston still completely there? Did you hear any noises in engine?

 

You need to do the basics first. Once they are done, post results, and we can see what route to follow.

VortecMAXi New Member

VortecMAXi

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  • Author
Posted

If the spring is not broken then something is causing the valve to stay open. Can you manually pull the valve up? Can you make the valve move at all? If the spring is not broken or collapsed, then the valve is either bent, or there is something mechanically holding the valve open. There could be something between the valve and valve seat, could be seized in the valve guide, or valve is bent. If the spring is broken, and you can pull the valve up by hand, you can change the spring with the head on the engine. I would try to rotate the valve to see if it can rotate freely, and can rotate freely in the closed position as well. To change spring with the head in place, take spark plug out, rotate engine to put that cylinder at BDC at end of power stroke, put adaptor into spark plug hole, connect air line to it. Use a valve spring compressor tool to compress the spring and remove keepers and retainer. Change spring and put it back together.

 

If spring is not broken, take the head off, flip it over and see if you can find a reason for the valve to be open. This is where you will end up sending head to machine shop for repair of bent valve or something jammed into the seat. You will also need to find out what happened. Change the timing chain recently? Is the top of the piston still completely there? Did you hear any noises in engine?

 

You need to do the basics first. Once they are done, post results, and we can see what route to follow.

 

 

Thank you for the thorough post!! I will try rotating the valve, I did not try pulling it up(best practice?). The spring appears to be intact. I did notice the rocker arm profile to look a bit abnormal (worn?not major) Looks like I will have to pull the head.

There are no noises. I have not changed the timing belt. If I do pull the head I will let you know how the piston looks.

 

This happened last week as I was driving on the 401. I thought I heard a little tap, then the dash lit up. Took it in for diag(dealer), performed a compression test on cyl 7 - <10psi. I have parked the truck since.

 

I see from your avatar that you are located in Ajax, small world, I live just east of you. Do you have a shop or know a good engine shop around town? Not too sure if I want to pull the head off myself.

 

 

Thanks again.

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