Date: Mon, 12 May 2003 19:40:28 -0700
Reply-To: wilden1@JUNO.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1@JUNO.COM>
Subject: Re: Check Compression: Warm or cold engine?
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In my aviation mechanic days, we ALWAYS removed plugs from a hot aluminum
cylinder head for a compression check, but NEVER re-installed the plugs
until the cylinder head was dead cold again. Put a cold plug in a hot
plug hole and the plug would seize in the plug hole and might never come
out. Case of the chilled shrunken steel ball/ heated expanded steel ring
experiment from high school physics. The mix of the steel (plug) and the
aluminum plug boss would be an even worse case scenario I would think. I
would think the same principle would apply to all the flat four engines
with aluminum heads including the WBX's.
What say you?
------------------------ Clip ---------------------------
I can't disagree with the policy published by Aviation Cylinder
manufacturers for their specific product.
Here, the true story: I removed a spark plug from a hot OEM Air Cooled
cylinder head and out came a good supply of threads with it.
I've always super tuned (tweaked) my engineers by reading the spark plugs
and I got anxious a few times sitting in roadside rest stops to see what
my last adjustments accomplished. You guessed it, got some threads.
I can't say that about AMC heads because by the time I ruined several OEM
heads I quit my tuning after I paid out the price of new AMCs. I just
practiced patience and waited for them to cool properly.
Some people don't like the anti seize but I have no opinion, it seems to
work but I stopped pulling plugs from hot heads so I'm just assuming that
it makes a difference.
I've just done simple center punch test on OEM and AMC heads and the AMCs
are harder alloy so they will probably fair better when removing spark
plugs.
It has been suggested that a light sanding of spark plug threads before
installation will remove sharp ridges and possibly stave off some thread
metal removal.
Since many Air Cooled and Water Cooled engines have been in the hands of
Impact Mechanics, individuals that don't know what a torque wrench is for
and just many plug changes over the years, it is possible to loose the
threads no matter what measures you take to preserve and protect them.
I'm just hoping that the statements that I've presented are true and
effective in making every effort to do the job without memorable bad
results.
One negative argument I've heard about anti seize is that it is an
insulator ........... I don't know about that but if it isn't on the
washer or the sealing shoulder I say, so what, let it insulate.
Stan Wilder
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