Burnt Exhaust Valve. Can a Rounded Cam Cause This?

[poorboy]

My brother's Turbo Limited had a tick, so I pulled the driver's side valve cover and sure enough, the #3 exhaust valve rocker wasn't moving much.

I tore the engine down and replaced the cam and lifters with a GM cam and GM lifters and put it all back together. Car started up fine and oil pressure came up quickly because I primed the engine. I was able to run the car for about 10 minutes at 3000 rpm before the #3 exhaust header started glowing red.

I had to leave the car for a month, and when I came back, I took off the heads as the diagnosis for the likely cause was a burnt valve. Sure enough, #3 exhaust valve was red.

I am going to put on another set of heads I have lying around, but the question I have is what caused the burnt valve? The engine had a slight miss when breaking in the cam, but it was barely perceptible to me, and a friend pointed it out.

Could the rounded #3 exhaust lobe have weakened the #3 exhaust valve? How come the #3 exhaust header didn't start to glow until the new cam and lifters were in?

 

[bison]

It's hard to say. Usually when you have a cylinder getting oil contamination in it it will get hot and potentially burn ex valves. The valve was probably burned before you put the new cam and lifters in.

 

[Chuck Leeper]

What Bison said^^^
Lack of lift, due to the lobe being damaged, could cause an increase in egt on that cyl. Still getting the same amt of fuel, but has increased gas velocity/heat, because the valve opening is significantly reduced. Once the valve began to warp, it's a "catch 22". Less seat contact = higher heat concentration=more warping. [Seat contact, even at hi rpm, has to be sufficient to transfer the heat to the cooling system.]

Back under my rock...

 

[charlief1]

One other possible cause is the valve was hanging just slightly open or the seat had sunk in the head so the valve didn't seal perfectly. Seen that before on NA engines.