On Mon, 19 Mar 2012 19:52:54 -0700, "PrecisionmachinisT"
wrote:


"Ed Huntress" wrote in message
.. .
On Mon, 19 Mar 2012 21:00:01 -0400, "Steve W."
wrote:

Ed Huntress wrote:
On Tue, 20 Mar 2012 00:23:24 +0000, David Billington
wrote:

Steve W. wrote:
Bob Engelhardt wrote:
There were 2 heads at the dump, each for 2 cylinders - from a a v4
engine I'd guess. Each of the heads had 1 cylinder badly "burned",
as shown. Anybody know what happened?

Just curious,
Bob

http://home.comcast.net/~bobengelhardt/EngineHead.jpg
Looks like timing belt/chain failure. That stuck 2 valves out in each
cylinder for the piston to hit. These break off then rattle around in
the cylinder and beat the crap out of everything. This is the end
result. You DID pick up those heads didn't you??? They are GREAT to
cut up, melt down and use for casting your own projects.

Typically they would be. A mate that works in engine development has
mentioned that the heads are invariably cast from virgin aluminium in
order to guarantee the material behaves as required, at least the major
players.

Generally they are 319 or 356 alloys, with some "fine tuning" for the
casting process in use. That's good stuff and good for casting by any
method -- particularly the 356.


I grab complete engines, rims, scrap pistons, rods and the like. Sort
them per claimed alloys then melt and ingot them.

I know that the melting changes the alloy some but for 99% of what I
cast they are close enough..

Sure. The big cast pieces, including the block and head(s), are really
good for sand casting or (in the case of 356) for plaster casting. I
don't know about 319 for plaster casting. It's probably Ok. Either one
can be cast in metal molds, too. 356 can tolerate fairly slow cooling
without dendrite enlargement, which can make them brittle. It would be
a good choice for casting in Petrobond, too, for the same reason.

Cast pistons typically are a high-silicon, low-thermal-expansion
alloy. They're really made for diecasting but they're pretty forgiving
(except to your cutting tools). You should be able to sand cast them
just fine.

I don't know about the other stuff. Little bits, like hose fittings
and the like, also are high-silicon -- often hypereutectic. They're
generally easy to cast. Structural parts may be 6061. You can cast
6061, although it's really designed as a wrought alloy.


356 basically means instant death to HSS tooling and carbide really doesn't
last very long either.


Any of the high-silicon alloys will precipitate some silicon, which
tears up HSS. 356 is around 7% -- much less than the eutectic level of
11.7% -- but the mix is not perfectly even and a bit of silicon drops
out of solution.

But the hypereutectic piston alloys are around 18%. At that level,
much of the silicon precipitates out upon cooling, producing crystals
that are real hell on conventional tools.

Diamond tools are the trick for production. But for onesies/twosies,
I've used HSS and just accept that you have to hone it after every
couple of parts.

--
Ed Huntress