Here is the piston to crank counterweight calculation, put in your own dimensions.
Quote:
As far as counterweights hitting the piston at the bottom of the stroke, the typical problem is the piston pin boss, ie metal below the piston pin. This thickness varies a lot from one piston design to the next. My Ross 99496 pistons have 0.150", Wiseco K296A35 have 0.220", my Venolias have 0.180". Everything must be checked at assembly for clearance, but this is the math:
CWmax = Counter Weight max dia
Pthick= Piston thickness below the pin
Pin = Piston pin dia
Rod = Rod Length
CWmax = 2(Rod - Stroke/2 - Pin/2 - Pthick - Clearance)
For example:
CWmax = 2(6.535 - 4.25/2 - 0.990/2 - 0.180 - 0.075)
CWmax = 2(6.535 - 2.125 - 0.495 - 0.180 - 0.075 )
CWmax = 7.32" dia
That happens to be the dia of the "cam cut" on a Callies 4.25" stroke crank counterweight for a BB Mopar.
Depending on the bobweight the counterweights can be cut down pretty far. I cut my Callies 4.250" down to 7.14" with a 2185 gram bobweight.
The rest of the counterweight can be larger since it isn't at BDC. My Callies was cam cut from the factory at 7.55"/7.32", but I cut it down to 7.14" dia (round) and balanced at 2185 gram bobweight. The balance shop went between the lathe and the balancer to get this close, don't just use my dia with other cranks and bobweights.
Another example:
CWmax = 2(6.535 - 4.375/2 - 0.990/2 - 0.180 - 0.050)
CWmax = 2(6.535 - 2.1875 - 0.495 - 0.180 - 0.050 )
CWmax = 7.24" dia
But the 6.535 rod with that stroke might not be a good idea. And it would need a piston CH less than 1.258"
