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Guest · Posted: Wed Mar 02, 2005 11:24 am Post subject: heat treat head?

Can an overheated aluminum engine head be heat treated (with weights on
it to keep it flat) to bring back its temper and hardness?

Joe

Tim Williams · Guest

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Robert Swinney · Guest

Not sure about weighting and heat treating aluminum - it sounds like the
source of more problems to me. Several years ago I had a severly warped
aluminum manifold on a small V-8. One clever mechanic recommended epoxy
under a new gasket instead of big $ for a new manifold. I went with his
idea. He kept the car over 24 hours for a "good cure" of the epoxy (I think
he used JB Weld). Success! I drove the car several thousands of miles
afterwards and nary a leak

Bob Swinney

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Lane · Guest

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Dave Hinz · Guest

On Wed, 2 Mar 2005 11:30:40 -0800, Lane <> wrote:

Robert Swinney · Guest

" Besides, head bolts under tension will probably exert more force on the
head in use than the weights would. And the head, in use, will see a bit of
heat..."

Yeah! Bit of heat is right! What caused my manifold to warp: The
thermostat came apart and locked itself in the closed position. Engine
overheated; stupid driver continued to drive until just before engine
seized; engine survived, heat caused aluminum intake manifold to severly
warp beyond sealing range of new gasket. Epoxy to the rescue.

Bob Swinney

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Mark · Guest

Not quite enough information. Ned to know the alloy.

For example, if the head is made in 356-T6 aluminum, then it was heat
treated at the factory. The T6 procedure is to heat the casting to about
1000 degrees (this is below the melting point of course) soak at that
temperature for a specific time (say 6-10 hours). The elements undergo a
homogenization process at that time. Then quench the casting in water very
quickly (immediately upon removeal from the oven). Then the quenched
casting is "aged" by placing it into an oven at a lower temperature, for
example 275 degrees. When this is done the elements that are held in
solution (due to the quench) will "precipitate" or come spontaneuosly form
within the casting. During the "aging" process the precipitates are formed
and these precipitates give rise to increased hardness and thus strength.

So by overheating you might have overaged the cylinder head meaning after
careful inspection (for cracks) the entire process would need to be
completed. The temps are approximate don't go by them to do a heat treat.
I worked at a foundry that straightened castings after heat treat. This can
be done for minor warpage. If the block was overheated the danger is for
knowing that in overheating the castings have "overaged" meaning the
strength is past it's maximum and could be softer (and less tensile
strength) than when it left the factory.

Mark

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