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From: gvcormack@watmum.UUCP (Gordon V. Cormack)
Newsgroups: net.auto.tech
Subject: causes of blue smoke:  ring wear vs. valve seal wear
Message-ID: <318@watmum.UUCP>
Date: Thu, 7-Nov-85 10:24:17 EST
Article-I.D.: watmum.318
Posted: Thu Nov  7 10:24:17 1985
Date-Received: Fri, 8-Nov-85 06:12:14 EST
References: <1278@ihuxi.UUCP>
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Organization: U of Waterloo, Ontario
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Many, many people have posted articles to the effect that blue smoke
on closing the throttle is a symptom of valve-guide wear, not ring
wear.  I think these statements are misleading.

In my experience, the symptoms are exactly consistent with ring wear.
There are a number of reasons why the smoke appears on closing the
throttle.  First, there is less fuel being burned, so that for a
constant amount of oil getting into the cylinder, the oil-to-gas
ratio is much higher.  Second, the combustion is not nearly as
complete, so the oil that gets in is not burned well.
Third, as has been pointed out, the vacuum tends to draw more oil
into the cylinder.  This happens whether the leakage is at the rings
or at the valve guides.

I have not conducted a statistically valid survey (I am sure the other
posters have not, either), but in my experience high oil consumption
is almost ALWAYS caused by ring wear and almost NEVER caused by valve
wear (5-0 on cars I have actually repaired).

A couple of tests have been suggested.  These tests can positively
indicate ring wear, but if they are negative they indicate nothing.
One test is the wet/dry compression.  If your compression improves
by adding a teaspoon of oil to the cylinder, the rings are certainly
shot.  A simpler test is to remove the oil filler while the engine
is running.  If puffs of partially burnt gas and exhaust come
out, the rings are shot (there should be a slight vacuum, assuming
your PCV system is working).

I won't argue too strongly against replacing both the rings and the
valve guides, but I think it is holding out false hope to suggest
that fixing the valves alone is likely to cure heavy oil consumption.

ASIDE:  It has also been suggested that it is impossible to remove
the oil pan on FWD cars.  In the vast majority of cases, it is indeed
possible, and is often easier than with RWD cars.