From: leavitt@cs.umd.edu (Mr. Bill)
Newsgroups: rec.motorcycles
Subject: Re: Roasting Headnut's on a striped down bike.......
Date: 15 Dec 92 22:39:41 GMT
Organization: The Cafe at the Edge of the Universe

TC>Problem: typical cylinder heads are 3-dimensional. What happens to the
TC>head, in thickness, as you heat it?

I should expect that it would expand vertically, ie: the material
expanding outward in all directions.  As you mention, the importance
of this is the variation in the thread pitch.  While the ridges would 
grow, so should the troughs.  In heating the block rather than the
stud, the pitch would change more for the tap than the bolt, and the
radial expansion would (hopefully) more than offset the thread variance.

Mr.B>applicable of which is removing studs from Chevy small block intake
Mr.B>and exhaust manifolds.  Heating just the studs didn't work much at all.

TC>You are comparing a steel head/steel stud pair to an aluminum head/steel
TC>stud pair. Apples and oranges.

Wherein came my query about aluminum vs steel expansion rates.  If
aluminum expands more than steel, this should help further in drawing
the head material away from the studs.  The benefit is even greater
here than in my steel/steel example.  The problems of variable thread
pitch do become worse here, but the diameter variation will also be
better.  Is the tradeoff positive or negative?  I don't know.  Maybe
we can pass the hat and contract for some more consulting with Llama
Materials Consultants, Inc.  8^)

Mr.B>So Tom, <bark bark bark> or from experience.  What, pray tell, 
Mr.B>are your qualifications <bark bark bark>

TC>Sheesh. Getting touchy? I merely asked you to explain your assertion, as
TC>an assertion without some backing information is, at best, suspect.

Urp, just a tad.  Gotta cut back on these 6 day/75+ hour weeks... |^P

TC>that a _block_ of metal be considered. This same block will also increase
TC>in thickness. Depending upon the engaged length of the threaded
TC>connection, and given the dramatically different coefficient of thermal
TC>expansion for the two materials in question (CTE=6.6* for steel vs 12.6 for
TC>aluminum [all in microinch/inch/degF, cuz that's what's handy]), the
TC>threaded lengths will change (or attempt to change) in a dramatically
TC>different fashion.

Again, now you're just thinking in the z-axis (along the length of the
stud).  Some x- and y-axis benefit will be derrived.  Maybe enough to
offset, maybe not.  I will admit that I've never tried a mixed composition
set, tho' I may get the chance when I pull Suzi's head off next month.
If this problem comes up, I'll try my method and post results.

TC>[*"Mechanics of Materials", Higdon, Ohlsen, Stiles, et al, John Wiley &
TC>Sons, New York, 1976, p. 674.]

Merci.  ;^)

TC>of heat appication is quite different (heating from within, rather than
TC>from an external source), which means that the temperature gradient will
TC>quite likely be different. 

True, tho' I don't think internal vs external application would be the
fault here, but rather the rate of heat deposition.  Operation would
cause a slower and more evenly distributed heat flow than you'd get with
a torch.

TC>The max temp may be quite a bit lower during normal operation 

At the surface, but not necessarily at the core, ie: towards the bottom
of the stud.

TC>(particularly if you're using an oxy-acetlylene torch to do the heating:-{).
>
Urp!!  |^P  Try propane.  O-a might well cause a small problem...

TC>>On a more positive note (and I've emailed the Mr. Nadzam on this), the
TC>>best results will likely be from heating and cooling the block. The

Mr.B>"Best results" vary, the only real measure being what works.  The same can
Mr.B>be said for what is "a more positive note" and what is, by Mr. Coradeschi's
Mr.B>insinuation, a negative response.  I certainly saw none of this in my post.

TC>Sorry to have given the impression of negativity. Relax. Have a homebrew.

Damn fine idea.  Let's see, I got in today about 5:30am, so I can probably
get to leave by about 8pm.  Yeah, a couple of homebrews sound *real* good...
X^}

I'll sure be glad when this test is over, and I can resume my life <*sigh*>

TC>                tom coradeschi    <+>    tcora@pica.army.mil

Mr.B>Mr. Bill
-- 
Bill Leavitt  DoD: #224  Domain: leavitt@cs.umd.edu  UUCP: uunet!mimsy!leavitt
1982 CBX (White Lightning), 1982 GS850G (Suzibago), 1976 CJ360T (Little Honda)
"Due to circumstances beyond your control,                               =o&>o
=o&>o                   you are master of your fate and captain of your soul."