1981turbota

^ there is also no discernible taper with the bronze guides as well.

08VRZ06

Very Interesting..... How did all the valve stems check?? Were any undersized??? Will you be cutting any of the exhaust valves open to check wall thickness and the drilling of the valve stem for being centered??

Thanks for the info.....

Mark

jedblanks

That was my next question. We know/conjecture/assume it's guides but what if it's guides and valves?
This (albeit generic) link mentions the top two reasons for failure:
(1) mechanical / thermal over stress
(2) Valve defect (1 in 5 failures)


So mechanical overstress would be - worn (or mis-machined) guides (or seats)
Thermal overstress would be - bad tune(or is it the ethanol in fuel???) or M1 not doing it's job
Valve defect could be machining error or metal defect.

EDIT: I found this interesting, though I can't verify the source:
wikipedia LS Engine article
"A 3-valve per cylinder design was originally slated for the LS7" ...but was shelved due to complexity and the ability of the LS7 to meet it's goals with two valves.

Was it designed to have two exhaust valves and then later "re-designed" in the name of saving money?

0C_Williams@RPM

Valve stems were dimensionally perfect, at least with as measured with .0001 micrometer.

All the valves had small nicks below the valve lock area - see this on most of these - has to be done during assembly

Won't cut these valves -they are brand new - but I'll section one of those I have replaced.

08VRZ06

Thanks.... I asked cause someone else cut some exhaust valves open and found that the holes were not drilled on center and the stem walls were very thin. Thats good to hear that the outside dimensions are good!! Could the nicks contribute to stress fracturing of the valve head?

Mark

track junkie

The GM Engine Mechanical Service Information shows a maximum for valve seat runout of "0.002 in (Maximum)."

If your TIR readings are correct, both of the new heads you measured don't meet GM specifications on three of the eight exhaust valves for valve seat runout.

LT5 John

Thanks for you expertise, and the data you have provided. Much appreciated...

Z06_505

Thanks Charlie. For your research and the great set of heads in my engine that went through your shop.