[Azimech]

I once had a Citroën DS 21 Pallas semi-automatic 1968, running on LPG. The engine is a 2.1 liter 4 cylinder. I asked too much of that engine, so one day I started to lose power at high speed. Looking in the mirror I saw big plumes of blue smoke appearing, and extra intermittent power drops started to appear. After that I lost cylinder number 2. Examination proved the ignition timing was wrong, I burned a hole in the top of that piston. Those intermittent power drops were the result of engine oil being pushed out of the oilpan and into the intake manifold through the breather, at some moments choking the engine. Coolant temperature was always OK. Even on 3 cylinders the car was quite quick though, and a joy to drive. Even if the engine sounded a bit rough.

This is not comparable with super/turbocharged aircraft engines, car engines have their oil vapors fed back to the engine by law, burning them with the fuel/air mix. Since almost all aircraft engines use dry-sump lubrication, there isn't much oil to lose, except the oil mist in the crankcase that will be pushed past the other pistons due to the supercharged pressure in the intake manifold: the flow passes the intake valve and goes through the hole in the piston, into the crankcase.
The engines that spray a jet of oil against the bottom of the piston for additional cooling will lose oil, through the piston hole, at a disturbing rate. The risk of explosions in the crankcase increases dramatically because of the stoichiometric mix of fuel and air in case of a carburetted engine. In case of fuel injection, which happened right into the combustion chamber after closing of the intake valve, the risk of explosion is negligible.


Other forms of damage that can appear from engine knocking:

*Shattered ceramic isolators on the spark plugs/ Melted spark plugs. Since every engine has two spark plugs per cylinder, this will lead to only a slight decrease in power unless both fail, that's a lot of unburned fuel in the exhaust manifold. P47/P38/B17/B24 hate that, can lead to explosions in the exhaust manifold or turbocharger in extreme cases.

*Holes in the cylinder head. In case of a water cooled engine this will lead to excessive loss of oil due to supercharger pressure blowing past the intake valve and through the hole, under the camshaft cover. Will probably produce a lot of oil on the windscreen. In case of a carburetted engine: explosions through the crankcase breather can produce engine fire. Explosions under the camshaft cover may warp or dislocate the camshaft cover, may lead to engine fire and rapid loss of oil, in case of inverted V12's the scavenging pump will not return the oil to the oil tank, worsening the problem.

Sometimes the explosions rupture hoses between engine and oil tank: instant loss of oil pressure OR the scavenging pump leaks the oil into engine bay instead of refilling the oil tank.
Carburetted radials will blow huge amounts of explosive mixture in the engine bay and the spark plugs will ignite it, engine fire unless enough airflow past the cylinders.
Fuel injected radials will less easily catch fire and less severe due to injection when the piston is already half past it's compression stroke and the intake valve is already closed.

*Damaged bearings of the piston rod (clunking sound until the rod or piston breaks).

*Damaged bearings of the crankshaft (again clunking sound, shaft may break in two or engine block may burst, even explode).

*Damage to the valves/ valve seats. Will lead to backfires, loss of compression and possibly engine fire.

Some of these symptoms are comparable with running too long with high CHT or prolonged over-revving.
IL2 only drops power, plays a sample and ultimately stops the engine. In real life, engine fires were a big and common problem. IL2 doesn't model engine fire caused by abuse by the pilot.

In case you have a hole in your piston or cylinder head and don't want a burning or exploding engine: lower manifold pressure so it's under ambient air pressure, let the engine suck for it, fresh air from outside will flush the crankcase. And lean the mixture. If you're flying a multiple engined plane: cut off fuel and feather the prop.

Something else to consider: High manifold pressure combined with low engine RPM increases the risk of engine knock. Another reason why running with too much prop pitch, apart from the high torque, is terrible for your engine.