Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Mon, 15 Sep 2003 20:03:04 -0400
Message-ID: <redirect-2580663@logan.com>
Reply-To: "Dan Schaefer" <dfs155@earthlink.net>
From: "Dan Schaefer" <dfs155@earthlink.net>
Subject: Re: iv-p cold running engine.How cold is too cold?
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To John Wright:

You'll probably get an answer from some of the AP's on this (I'm not) but
I'll submit my two cents worth anyway.

It's my understanding that running CHT's too low will scrub out the cylinder
choke fairly quickly. The cylinders of most big Continentals (and many other
engines as well) are manufactured with the upper several inches tapered
several thousandths, e.g., they are smaller in diameter at the top than the
majority of the bore.

As I understand it, this is done so that when the cylinder head region
reaches "normal" operating temperatures (the upper part of the cylinder
being the hottest), thermal expansion will cause the choked area to expand
and bring the cylinder bore walls close to parallel.

If you don't run high enough CHT's, sufficient expansion will not occur and
the choke will go away through wear. Subsequent running at more normal
CHT's, after the choke is gone, will cause the upper part of the cylinder
walls to grow larger (diameter) than the rest of the bore when the cylinder
head region thermally expands. Plays havoc with compression at the top of
the stroke where it's most needed when the cylinder is hot - and isn't all
that obvious when it's cold.

Apparently, as I read the literature, CHT's that are outside of the
manufacturer's stated operating range, above and/or below, are
etrimental  - at least as far as engine/cylinder longevity is concerned.

Dan Schaefer