Found out what was wrong with my truck

[HareRazor]

Well the past couple of years I have had a head gasket slowly leaking on my truck. It was getting to the point that the bottom end was getting kind of noisy and it was not firing on all cylinders until it ran for about 10 minutes. I had started fitting a v8 in it until I came across a 3.0 with 80k miles on it for cheap. They said it had ran good, but I think they might be liars. I cleaned up the new engine, replaced front and rear main seals, timing cover gasket, valve cover gasket and oil pan gasket to try to prevent any coolant/oil leaks that I had issues with previously. I installed it and fired it up and there was a dead miss. Compression check on #6 gave 0 and the rest were ~145 - 150. The bottom end sounded good. I hooked up an air hose to the spark plug hole and it was going straight out the tail pipe. I pulled the heads and this is what I found.

That is on the exhaust valve. The piston and the cylinder walls feel fine still, so I think I am fine with just replacing the head. What would cause an issue like this as I want to prevent it from happening in the future?

 

[Big Jim M]

An exhaust leak at the manifold next to that valve will doit every time.. What happens is on the intake stroke AIR is pulled into the cylinder thru the leak and the exhaust valve gets the brunt of the high temprature..
Big JIm

 

[HareRazor]

The engine didn't come with exhaust manifold gaskets on it(nor did mine), but I am putting it back together with them. I got the head, lower intake, and exhaust manifolds all cleaned and reassembled today so I should get it fired up tomorrow and hopefully all will go well.

 

[Rearanger]

An exhaust leak at the manifold next to that valve will doit every time.. What happens is on the intake stroke AIR is pulled into the cylinder thru the leak and the exhaust valve gets the brunt of the high temprature.Big JIm

Ok, you're going to have to go deeper into this for me to agree. When the exhaust leak starts the valve is not leaking, how would the intake stroke then draw air into the cylinder through that valve? With the other cylinders also exhausting and providing exhaust pressure, how would air be sucked into the exhaust valve?

 

[McCormack]

If air was being drawn in the air would have a cooling effect on the valve.

 

[HareRazor]

I am not sure, but I got the truck back together yesterday and it runs great.