At 10:11 AM 5/2/2001 -0700, Max Heim wrote:
>....
>I suspect it really isn't that critical for the oil pressure gauge to have
instantaneous response in these cars, anyway. I have to admit I once drove
my car a 1/2 mile with no oil in the sump before I noticed the gauge
bottomed out, with no apparent ill effects ....
Well I'll tell you, when the oil pressure fails I want to know about it
IMMEDIATELY. While it is possible to drive a short time at moderate speed
and light throttle with virtually no oil pressure, the same cannot be said
for top end power. I have learned the hard way (more than once) that when
oil pressure fails at around 7000 rpm and full throttle it only takes 3 or
4 seconds for disaster to set in.
At that speed the mass of the con-rods generates a very high centrifugal
force that is on the verge of overloading the bearings. When oil pressure
fails the flow stops, and very shortly the oil film overheats and breaks
down, followed by friction melting of the white metal bearing material,
which then flows out the sides of the journal like hot wax. If you don't
notice the loss of oil pressure, the first indication of a problem is when
it feels like someone is stepping hard on the brake pedal as the melteing
bearings are dragging heavily on the crank journals without lubrication.
If you kill the engine at that point the bearings will cool and solder
themselves to the crankshaft (making disassembly a PITA). If you slow it
down some and the oil pressure and flow happens to return, then the
bearings can cool and solidify without seizing on the crank, which leaves
you with very nasty rod knock and very low running oil pressure.
Now under racing conditions you may not be looking at the pressure gauge
anyway, in which case oil pressure failure would be well accompanied by a
large red warning light and very loud buzzer. Just a thought.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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