David Massey wrote :
>
> How about this: As the bronze heats up and expands it is restraned by the
> head (or the remnants of the old guide) and is compressed further onto the
> valve stem.
Yes, but by how much? Coefficient of expansion for gray cast iron is given
as .000006, one variety of manganese bronze I found is given as .000010, per
degree F. The guide clearly exerts force on the head, which would deflect
by some amount ...
> Isn't bronze a copper/lead alloy and would embody some of the self
> lubricating attributes of the lead?
Depends on exactly which bronze it is. The only hard requirement to be
called bronze is copper alloyed with something else. It was originally an
alloy of copper and tin. One definition of manganese bronze has 6%
aluminum, 3% iron, 3% manganese and 25% zinc; with only trace amounts of
lead, nickel and tin.
http://www.anchorbronze.com/c86300.htm
Randall
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