5.7 L Vortec - Burnt valve?

[ProCombat]

So I picked up a 1999 2 door tahoe in amazing shape for real cheap. Guy really didn't know what he had. It starts good, but is losing compression from a cylinder. It sounds like a bad valve. I'm towing it to my place tomorrow, and hopefully opening it up and finding the problem. I'm hoping it's just the head(s), and I can get it replaced or fixed for pretty cheap. I can do the work myself in my garage.

Has anyone else seen this problem before? I haven't gotten too deep into the engine of a gmt400 yet. Any tips, advice, or similar stories would really help me. Thanks!

 

[SixSpeedSS]

I bought my 1996 K2500 Vortec with low compression in one cylinder. It ran fine but wouldn't idle in gear. One cylinder was ~60psi. When I tore it apart I found both heads were junk (cracked in between the center ports and all combustion chambers were a blueish color). My guess it got really hot at one point. Also had a bent connecting rod in #2 cylinder.

I would certainly do a compression test on all cylinders to make certain which cylinder has a problem. Once you find the bad cylinder, I would try loosening the exhaust rocker arm (only on that cylinder) and see if the compression test changes. A cylinder leak down is probably the best way to find a burnt valve or broken ring. Otherwise it has to come apart and inspect.

How many miles on it?

 

[ProCombat]

It has 150k miles on it. I was planning on taking it apart anyway.