Scott Gardner wrote:
> Maybe you can help clear up a fuzzy picture in my mind. When you
> hear of somebody missing a shift and "airmailing a piston through the
> hood", is this just a figure of speech?
It would be very unlikely that a piston could make it through the
hood. Most pistons are aluminium and just don't have the mass to
overcome a head or block. Now a rod.......
>What is the physical damage
> to an engine when somebody "blows a piston"?
Most of these terms are vague slang. Blowing a piston can mean anything
from burning a hole in it, to totally destroying it. Debris in the
engine is the most damaging, it will be circulated throughout the engine
with the oil, scratching and scoring as it goes.
>Can it really separate
> from the con rod and break through the head?
Pistons can seperate from the rod, usually breaking at the wrist pin
point. At this point the piston usually is just left sitting in the
cylinder, or the rod bashes it one more time to TDC. Once the rod
seperates from the piston it can 'point' to where it wants to, limited
only by the cylinder, sometimes. The rod can poke out of the block
for example, at the block skirt, which is thinner than the cylinder area.
>Or does the con rod
> usually stay with the piston and separate from the crank?
This can happen too. Different engines have different weaknesses therefor
different ways to explode. Usually when a rod seperates from the
crank it is a failure of one of the rod bolts or the cap. The crank will
spread open the rod cap, eventually seperating the two.
>While I'm
> thinking about it, what does it mean to have "spun a bearing" in an
> engine?
This is when a plain bearing spins in it's bore, ie the bearing is
rotating with the crank shaft rather than staying stuck to the block or
rod.
>The only catastrophic engine damage I've ever seen
> personally is a broken crankshaft, but the owner just noticed a bad
> noise, tore down the engine and found the problem.
I remember a story about an old Buick straight eight. The crank broke
seperating the front two cylinders. The engine ran fine, the car
drove, the only clue was that it was down on power, and the crank
shaft pully wasn't rotating-so no charge or cooling.
Most of the extreme engine damage you are asking about happens due to
over revving, spun bearings can be from just age/wear too.
Some performance shops/drag racing shops will have displays of mangled
parts, always entertaining.
The best I have is some bent valves from a '63 T-Bird.
-Aron Travis-
"always in a automotive frenzy"
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