DeTomaso Mailing List: April 98, Message #88

-> After they took the lead out, they began induction hardening the
-> seats in cast iron heads.  Anyone know what that process entails?

 The head goes into a fixture with loops of copper tubing at the valve
seats.  The copper tubes are the conductors for a few hundred amps of AC
at .5 to 150 kilocycles.  (Down with Hertz and meaningless named ISO
units!)  The eddy currents induced in the workpiece heat the area by the
loop, which is carrying a flow of coolant so it won't melt itself.

 Induction hardening of valve seats goes back at least to the 1930s.
It was not often used.  Chevrolet, after their horrible debacle with
their mid-late '70s small blocks, went to induction hardening the seats.
You can see the discoloration around the seat in a brand new head, or
one you've just pulled out of the caustic tank.  A few others did this
as well, but not many, and Chevrolet largely discontinued the practice
by the mid '80s.

 Seat recession happens, but in my experience it's not an unleaded gas
issue.  The few cases I've come across always had severe lifter, rocker,
and/or pushrod wear along with the bad seats, leading me to believe the
seats were simply pounded to death.


-> BTW, it looks like the Motorsport aluminum heads have cast iron
-> seats.

 Which is fine; cast iron of any of several alloys makes a fine valve
seat.

==dave.williams@chaos.lrk.ar.us======================================
I've got a secret / I've been hiding / under my skin / | Who are you?
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