[TR] Valve Composition

[terryrs at comcast.net]

Hello everyone.

Tried searching archives but can't seem to make it work.  

Question:  While the head is at the machine shop I'm having the seats hardened.  What are the various metallic make-ups of valves anyway, and are stainless steel ones best?

Question 2:  Since I'm replacing the valves, guides and springs anway on a TR-4 head of unknown vintage, I can choose either the 3/8ths or 5/16ths and either will fit, right?

Terry Smith, '59 TR3A TS58667
New Hampshire