Re: aluminum head damage - again

["James J." <m1garand@speakeasy.net>]

Craig,
   The T6 process involves an initial controlled heating to ~900DegF 
followed by a second heating to ~300DegF followed by quenching, etc.  
The second heating is just an aging process.  Welding instrictions for 
T6 repairs recommend a max. pre-heat of ~250Deg F.  So where am I going 
with all this?  Did you use radiant heat to cure the powder or put them 
in an oven?  Was it just for 20 minutes?  If you used raidant heat, like 
I do, with one surface cooked at a time, the heat probably never 
penetrated deep into the heads.  If you put them in an oven, more of the 
material was likely affected.  Still, after only 20 minutes, the heart 
of the castings probably weren't all that hot.  I know that plenty of 
companies apply thermal compunds to the combustion chamber surfaces, 
which require curing at ~300+ for an hour. 
   But here's the meat:  Let's not forget that the chambers, the 
exhaust ports and the mounting flanges for the exhaust manifold see 
temperatures approaching ~1000DegF for most of their lives.  I'm gonna 
go out on a limb here and suggest that the T6 process used here is more 
about "annealing" or stress reducing the casting than it is about actual 
heat-treating while giving the manufacturer some glitz for the sales 
brochure.  Heat treating won't affect the thermal expansion properties 
of the base material, so if your head was going to drop a seat or a 
guide, it would do it regardless of powdercoating or not.  I just don't 
see how an aluminum head can be expected to operate in an environment 
that doesn't violate the T6 treatment in several key areas, including 
the material holding the seats and exhaust stems.  Someone correct me if 
I'm missing the obvious.
JJJ


FAUBEL CRAIG wrote:

> I powder coated my new aluminum heads.  I want to find somebody who has actually done this and finid out what the outcome was.  I've heard information from 'experts' and amateurs that is contradictory.  I've researched until all I'm sure of is the heads are A356 aluminum that went thru the T6 'tempering' process.  I see all kinds of motorcycle heads get powder coated, and they're made of the same stuff.  When I find somebody to tell me what actually happened - either they work fine or they exploded after 100 miles -  I'll stop asking.  Can someone help?  I'm out of ideas where to look and who to ask.  I don't want opinions any more, but just how do I find someone who did this...  I know I'm not the first one to be ignorant enough to try it, and I know it's not recommended (but you'll never find anybodt to say it's OK to put in a light switch without turning off the breaker, and we all know that it CAN be done), but it's already done and I don't want to throw the $1200 heads !
> away
> unless it is hopeless.  
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