Matt,
Preheating of any cast material is a good idea, as it greatly reduces
the latent thermal stresses that cause cracking either during the weld, or
during cooling, or much later when a stress-riser fails under an otherwise
normal stress. It is very improtant to pre-heat aluminum castings prior to
welding, more so than cast iron.
Aluminum heads (and blocks) carry heat away from the source much quicker
than cast iron does. That's why we can run higher compression ratios with
aluminum heads. Perhaps the ridges in the CNC heads never get hot enough to
cause detination (I'm asuming they were aluminum?). If that;s the case,
perhaps I don't have to worry about the pitting in my heads as much as I
would were they Iron.
Hmmmm, still, 1/8" in high ridges would seem to hinder flow, in my mind, but
I'm sure those guys know what they are doing, or else no one would buy their
heads.
James J.
-------Original Message-------
From: Matt Junker
Date: Friday, December 19, 2003 2:16:48 PM
To: James J.
Cc: mgb-v8@autox.team.net
Subject: Re: Looking for a lonely 300 head
James,
correct me if I am wrong, but I believe that you only have to pre-heat cast
iron to weld it.
The CNC marks I saw in sprint-car heads were rather rough (guessing
eighth-inch high ridges).
[demime 0.99d.1 removed an attachment of type image/gif which had a name of
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