Preheating engines: Airplane engines versus auto engines

On Dec 22, 6:15 pm, wrote:

Many pilots seem to believe that blow-by in the engine is a
normal operating condition. My experience( and opinion) and that of
many other race engine mechanics that I have talked to, is that once
combustion gases begin to leak past the rings, the end of that engine
is imminent and soon. Very soon. Blowby totally destroys the
lubrication of the piston in the area of the blowby, and it shouldn't
take a rocket scientist to know what that means.

regards,
Bud

My experience is as an aircraft mechanic. Part of the
inspection process is the differential compression test on each
cylinder, when it's hot after shutdown. All cylinders leak a small
amount past the rings, and when the engine cools the leakage is
considerably worse. All rings have ring gaps, and unless you have
stacked rings (two rings in the same groove) you cannot stop the
leakage. Aircraft engines do not have stacked rings.
The fact that a frozen-shut breather will cause the front seal
to blow out is enough evidence that rings leak.
The volume of the crankcase, as noted earlier, is very small.
The amount of water in a cubic foot of air, even if it's saturated, is
miniscule compared to that which gets past the rings curing
combustion, unless the aircraft is parked for a long time and the
heating/cooling cycles of day/night pump air in and out repeatedly for
a long time. Water, even a small amount, mixes with oil and in the
presence of metal, which acts as a catalyst, breaks the oil down and
creates acids. The thin film of oil on the parts is the first
contributor to this process and is not much protection at all.