<VV> Rod caps and balancing

[Cliff]

Eric makes a good point, except he is mistaken about the rods on a Corvair. 

The big ends do not travel together.  Each connecting rod has its own
journal on the crankshaft and the paired rods actually travel in opposite
directions.  When #1 is at TDC for compression, #2 is also at TDC for
exhaust. #5 and #6 will both be at BDC and #3 and #4 will be somewhere in
between. 

My blown 140 is sitting on the bench and I just looked to confirm my
suspicions. 

Cliff Tibbitts
Lexington, KY

<snip>
I don't buy that. Think of a two cylinder opposed engine, the big ends go
around together. The small ends going back and forth are going the same
direction, so they are not canceling each other, they are helping each
other. What keeps it balanced are the pairs of cylinders canceling each
other out.
  The total of 1&2 needs to equal the total of 3&4 which needs to equal the
total of 5&6.  The counterweights are the two other pair. Big end & small
end/piston. That way as two pistons are going to the left at full speed, 4
are going to the right at reduced speed (one of each pair is leaving BDC,
and the other is leaving TDC).
   
  Long story short... balance ALL rods & pistons.
   
  Eric

    <Snip>
   The way a 'Vair engine is put together is pretty much tantamount to three
2-cylinder engines sharing a common crankshaft. The opposing pairs of
rods/pistons simply don't interact with other opposing pairs... unless
something is VERY MUCH different as regards weight and even then it's not
gonna amount to THAT much vibration. 

This is why a 'Vair crank gets away with having no counterweights. 
<Snip>



       
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