Re: Exhaust Valves
From: Big Block Chevy Marine Performance
Exhaust Valves:
The exhaust valve, because of higher operating temperatures, is a
two-piece design made of stainless steel and high alloy carbon steel.
Stainless steel can resist higher operating temperatures and is more
resistant to the corrosive effects of the exhaust gases, but it cannot be heat treated to a hardness that will keep the valve stem end from wearing rapidly between the stem and the rocker arm. Because stainless steel valve stem ends wear faster than regular steel, engine manufacturers go to a great deal of trouble and expense to manufacture a stainless steel exhaust valve made of two pieces. The valve stem is made of heat-treated high carbon alloy steel for a hardened stem end and the valve head is made of stainless steel, then the two-pieces are welded together. A two-piece welded valve is, contrary to the aftermarket valve manufacturers' claims, perfectly fine for any application and will cause no problems.
Stainless Steel Valves:
A one piece stainless steel valve can resist higher operating temperatures and is more resistant to the corrosive effects
of the exhaust gases, but as mentioned, it can't be heat-treated for
better durability. If you have ever looked through a camshaft catalog,
you might have seen something called a lash cap. This is a little cap that fits over the valve stem end and keeps the rocker arm from wearing it out. Lash caps are used primarily on one-piece stainless steel and titanium valves. When aftermarket valve manufacturers claim that their stainless steel valves can be directly interchanged with original equipment valves because they have a hardened stem end, they are really saying that a hardened steel stem tip has been welded to the end of the valve stem above the top lock groove. These valves are not considered to be, in my opinion, a one-piece stainless steel valve.
