I was wondering how important it is to precisely balance a crankshaft so I did
a little oversimplified math - For each crank rotation each counterweight
changes from overbalanced to underbalanced 8 times - If the piston and the top
of the rod weigh 1 1/4# and the balance is for the normal 50% of the recip.
weight the ajacent main bearings get pushed and pulled by 5/8# times about
2000 gs (7500 rpm 4" stroke) or 1250 lbs. - If the crank is off by 1 gram
(.0022 lb.) X 2000 gs , instead of 1250# that main bearing sees 1254# one way
and 1246# the other - 1 gram is even less important if the downward force of
the combustion is included .
|