I realize I'm dragging up an old thread, but I need some clarification, and am hoping to get some here! Aerohead, can you provide a source for this information? I'd like to do some more reading on this idea.
I've been wondering what causes the "shaking" feeling when you lug an engine - this momentary welding and fracturing or the crank journal-to-bearing-surface would certainly explain it. Simple bearing contact would not!
Thanks!
-Mateospeed
Quote:
Originally Posted by aerohead
sickpuppy,I think your's was the first use of the term "jerk",which I understand as an "instantaneous acceleration." Under some of the extreme "lugging" scenarios mentioned,I understand that if jerk occurs,the bearing journal can actually displace the oil film,achieving "high-point",where there exists momentary metal-to-metal contact between the journal and babbit material.Instantaneous friction-welding and then fracture-release can occur,and this is basically the beginning of the end for both surfaces.I have been told that the switch to automatic transmissions for Diesels,has happened in part do to broken crankshafts due to "jerk",when operators let rpm's drop too low.Evidently,the torque-converter on an automatic will stall before rpm's can drop to a level where jerk would occur,protecting the crank.
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