Lawrie,
A few points I would like to discuss with you.
First if you drive a car into the shop and turn it off and remove the valve
cover and start adjusting valves, by the time you get to valve #8 the engine
has cooled somewhat. Maybe only 10 or 20 degrees but you have to admit the
engine is no longer at operating temp. (don't forget not everyone who is on
this list, can adjust valves as fast as you can, they don't get the practice
you do :-) If the engine has cooled by the time you have reached valve #8
then not all the valves were adjusted under the same conditions. If on the
other hand you are working at room temp. the valves will all be adjusted
under the same conditions.
Secondly, as far as coefficients go, wouldn't you agree that differences in
expansion coefficients is a function of differences is materials, not wear of
those items? (regardless of how worn it is, aluminum expands at a different
rate than iron.)
BTW one of the engines I teach on has a new valve adjustment spec that
SPECIFIES 20 degrees C (68F) and has corrections for each 1 degree C variance
from that temp! (The clearance changes by 0.01mm for each degree C)
The differences we are discussing are small and perhaps, not worth the
bandwidth, but I like doing my valves cold.
Rick Ewald
In a message dated 8/17/99 7:40:34 PM Pacific Daylight Time,
Lawrie@britcars.com writes:
> In my experienced (and not-so-humble) opinion, valves should always be
> adjusted when they are hot. After all, they do their work when they are hot
> and that's when the clearance is critical. Who cares what the clearances
are
> when the engine is cold and at a standstill? And, yes, I know a lot of shop
> manuals state that clearances should be set when the engine is cold, but
> they were written when all the valve train components were new and
> co-efficients of expansion throughout the valvetrain could be relied upon
to
> be fairly uniform. We are mostly dealing with old, worn engines where some
> things may expand at different rates than others So, if the book gives a
> "Cold" valve clearance, just subtract 2 thousandths from it and set the
> clearances when the engine is at running temperature.
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