<WOB> Re: Today's Flame

["Jacob J. Steijn" <jacob.steijn@xxxxxxxxxxxx>]

>>> Lugging is supposed to be "bad" for your engine.

You bet!  It's called "metal-on-metal" or "rapid wear."  Lugging means
putting a load on the engine at too low a speed.  It's bad because it put's
an extra heavy load on the crankshaft/main bearing surface and the
crankshaft/connecting rod journals while depriving them of the hydrodynamic
film of oil that normally prevents metal-to-metal contact.  Normally these
parts never touch each other, because they ride on a layer of oil.  That
layer of oil is maintained by the relative motion of the surfaces and the
viscosity of the oil - that's why viscosity breakdown is bad and why the
old saw that most wear takes place in the first few seconds is true.  

When you lug, you run the engine too slow to maintain the hydrodynamic
film.  You also run the engine outside of the design parameters for
combustion and ensuing high pressure and force on the piston.  The engine
is designed so that combustion takes place as the piston moves beyond the
top dead center.  At high speed you have to ignite before tdc so that
combustion and pressure occur when the crank is at maximum leverage (90
degrees after top dead center, right?).  At lugging speed, all that force
slams the crank down onto the journals and little of it turns the engine.
No engine is designed for this.

Need more coffee.  See ya.
But then again, I might be a maroon baboon <insert burp here>
Jacob J. Steijn, Delaware Valley Chapter. BMW CCA 135150
'88 M5 daily driver
Wilmington, Delaware

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