[AMC-list] I know why 195.6 ohv heads need re-torquing

[tom jennings <tomj@xxxxxxx>]

I know why the 195.6 OHV head needs to be retorqued, and maybe how to solve
it.

Thermal expansion.

The head is what, 30" long? (Don't have one here at work...!). It rises 140F
in normal operation (60F to 200F, say, and that's assuming no overheating
and impossibly even heating). The coefficient of expansion for cast iron is
5.8 microinches per inch, per degree F. That's .024" increase in head
length! It cycles cold, hot, cold, hot, ... every time you drive the car.

We know for fact that on this motor the head gets hot VERY FAST. The
combustion chamber is over an inch deep in the head, with a lot of area
(that oddball wedge). The exhaust passageways through the head are long.

Read this and watch the video: http://www.boltscience.com/pages/vibloose.htm

 Plus, the head is heat-insulated from the block with the composite gasket
(a copper gasket would be nice!). Therefore, the head grows more and faster
than the block, by a big margin.

All this simply walks the bolts out. Because they are bolts, they have a lot
of torsional stress; they are therefore predisposed to untwist to begin
with. Add to it slowly crushing gaskets, too much or wrong lube (probably my
problem) heat-softened, age- and overtightening-worn old bolts (probably my
problem) just makes it easier and more likely to happen in 2010 than it did
in 1963.

The Permatex lubricates the sliding.

* Head studs and the right lube will help a lot.
* Increased torque for ARP fasteners will help a little more.
* Extreme attention paid to head cooling issues!!

PRECISE LOCATING DOWELS. I'm gonna ask around about dowels. The differing
head vs. block growth rates though means the head will try to shear them off
the block. That obviously won't do.
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