>> view mirror I was getting puffs of smoke as I changed gear (on the
>> overrun). I discussed this with a friend and we decided it must be
>> the valve guides which were worn and oil was being sucked in and
>> burned off on the overrun.
>
>Nope, the valve guides will cause it to smoke the most on start-up. It
>sounds like rings to me. When you shift gears, there is a vacuum in the
>cylinders which helps to draw the oil past the rings. That's why it doesn't
>smoke under load, there is pressure in the cylinder preventing the oil from
>getting past the rings.(as much) Under load, there is a stronger vacuum in
>the intake ports due to the velocity of the flow, this would draw _more_ oil
>from leaky valve guides.
Actually I'd disagree. When you upshift, assuming you don't try
to burn your clutch up you take your foot off the gas. You've now just
gone from open butterflies to closed butterflies at high RPM. The intake
will have heavy-duty vacuum in it, especially compared to on-throttle
operation. This can really suck the oil past the valve guides. The
rings do experience a bit more vacuum for longer than normal, but not to
the degree that the valve guides do. Usually with bad rings you burn oil
more continuously, since the rings aren't removing the oil as the piston
goes up and down. The other symptom of really bad rings is lots of blow-by.
IHMO, of course.
Randell Jesup
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