[Shotimes] Low pressure, high volume?

[George Fourchy]

On Mon, 23 Aug 2004 01:13:27 EDT, Bobbonnit1@aol.com wrote:

>I can't for the life of me, figure how rod bearings  would not get enough 
>lubrication for the short period of time that one would  "lug the engine". 

It's not a short period of time.  Its a bit here, a bit there, and a bit more here,
there, and on and on for months or years.  Damage from lugging an engine won't show
up 'now' (back when it was a year or two old).....it shows up _later_ (now), when
it's 14 or 15 years old.

>You 
>would think that the upper end would run dry and you'll  ruin a cam before 
>making a rod bearing spin. Before it spun, it would have to  run completely dry 
>until friction grabbed it and pulled the little tab that  holds it in place 
>completely flush!  

1.  The cam and lifter oil supply comes off a separate oil gallery (passsageway from
the pump) than the main and rod bearings, and flow to it may or may not be affected
by low pressure or oil level.  2. You'd be surprised at the amount of destructive
energy in a connecting rod that is able to build up a little bit of straight line
inertia against the crank journal.....and again, the clearance required for the
damage to occur appears over a period of time.  A cam lobe is hardened, as is the
lifter or shim, so they are a little bit (a lot, actually) more durable than the
soft metal of a bearing shell and a crank journal.  And it doesn't need to be
completely dry....the single layer of lubricant molecules just has to fail for a
tiny micro-second.  Also, remember, when there is wear along an entire bering shell,
so that the shell's radius is a lot larger than the journal, the point (and oil
film) where the journal DOES come close to the bearing shell is under MUCH more
pressure than when radii are the same (when it was new).

>What are OEM bearings made of  anyways?  Is being made of too 
>soft of an alloy cause premature failure in  early SHO's?  Are replacements made 
>of a harder metal? What's the  difference (as far as rod bearings go) in 
>lugging the engine or turning over by  hand during assembly?  Why don't they make 
>a high volume, high pressure  pump.......too much lube is a good thing right?  

They are made of an aluminum shell with copper and lead alloys covering the
lubricating surfaces...very soft on purpose to protect the polished journal...the
oil does all the work.  There is no difference in bearings other than improvements
in surface metal alloys (for all practical purposes) found in any car engine dating
from the 40's-50's  to now.  They all do basically the same thing....the oil is what
has improved.  Not sure what you mean by turning over by hand during assembly....one
uses thick oil or assembly lube to put an engine together; also when a new engine
starts for the first time, wear does occur at a rapid rate....things are just
designed to allow that to happen, and when the wear is done, after break-in, the
clearances are what they need to be for long life.  Too much oil pressure will lift
the bearing out of its spot in the rod, disengaging (and allowing bending of) the
tang, and allowing the shell to spin much sooner in the engine's life, all other
variables inside the engine being the same.

Wet sump oil lubrication systems are very finely designed.....you can't second-guess
design engineers (especially Yamaha engineers) this easily.  In my
experience....playing hard with engines since the '60s...no one group of folks has
asked their cars' engines to last as long as these are without attention, and the
original engineers didn't think they would.  It's our 'fault', and we have to make
the allowances.  Be easy on them, or rebuild them.....take your choice.

George