Originally Posted by S10 Racer
I have a chance to get some recently redone 781 heads for my 454. The valves come with the heads but are not installed yet. Is there a way to tell if the valves are stainless or not? Can I use a magnet to tell? Also, the guy says the guides have "liners" instead of bronze guides or knurled. Is this acceptable for a performance build?
- A guy that says they have "liners" instead of bronze guides, needs to be more descriptive. Typically press in guides are either some sort of a bronze alloy or are cast iron, either is suitable.
- Some stainless alloys are magnetic some aren't. Valves will be of some sort of stainless alloy unless made of titanium.
- General description of the more common stainless alloys:
*Austenitic: Chromium-nickel-iron alloys with 16-26% chromium, 6-22% nickel (Ni), and low carbon content, with non-magnetic properties (if annealed - working it at low temperatures, then heated and cooled). Nickel increases corrosion resistance. Hardenable by cold-working (worked at low temperatures) as well as tempering (heated then cooled). Type 304 (S30400) or "18/8" (18% chromium 8% nickel), is the most commonly used grade or composition. Grades run from 100 thru 300 series
* Martensitic and Ferritic, these are 400 series.
Martensitic: Chromium-iron alloys with 10.5-17% chromium and carefully controlled carbon content, hardenable by quenching (quickly cooled in water or oil) and tempering (heated then cooled). It has magnetic properties. Martensitic grades are strong and hard, but are brittle and difficult to form and weld. Type 420 series is an example. Ferritic: Chromium-iron alloys with 17-27% chromium and low carbon content, with magnetic properties. Type 430 series is an example.
*There are other grades in the 500, 600, 700, and 900 series. Inconel is one in this series that's often used in valves it's actually an austenitic type, very difficult to form thus expensive, but really good stuff.
Valves need different qualities (especially the exhaust) between the head and stem. The head is usually a cold worked ferritic steel for its strength at extreme temperatures while the stem needs to pass heat to the cooling system and resist wear so they are usually the martensitic alloy. The stem is then friction welded to the valve head by spinning them at high speed and slamming them together with extreme pressure. Other processes are used on better quality valves to put hard wearing surfaces on the seat area like Stellite and sometimes a hard tool steel wear cap on the stem end to increase wear life against the rocker arm. Stems often are available with a hard chrome finish to assist in wear quality. My personal like is for chrome against bronze alloy guides as chrome doesn't oil wet well and bronze is better at becoming oil wet than cast iron, so with positive oil seals on the guide, I prefer the bronze guide, chrome stem combination with lifts about a half inch or more.
- Go here for Manley's descriptions of their products which leads you from common street valves to uncommon race hardware.