For those who asked for the dimensions, there are 2 way of doing it. They both use the same dimensions to cut out the blank. The first is cut from 1 1/4" thick material and part of the "ring" is milled away to give a counterweight like the ones Bob showed above (which I expect are made to these dimensions). The simplest ones are cut from 5/8" material (the same thickness as the round part of the crankshaft where they are mounted) Now for the dimensions:
- Draw a straight line and put 2 centre points 1" apart on it. The line is the centerline of the finished counterweight's.
- About one of the points, draw a 4" diameter circle. That becomes the hole that is later machined ready to be shrunk onto the crank shaft
- About the other, draw a circle 6 1/2" diameter circle. That is the outside of the C/W
and there you have it - simple
For the thicker ones, the line where the extra metal is milled away is not at right angles to the centerline. It is about 12 1/2 degrees off and since the counterweights face both forwards and back, you will need 2 cut each way.
Attaching them to the crankshaft is up to you. A good shrink fit (allow 0.001 plus 0.001" per inch of diameter for shrink) should be enough but the comfort of a setscrew or bolt or weld as well is OK. If you weld, you might want to check the crank for straight afterwards.
IMO, the simple ones are enough. After all, there have been lots of Model As do lots of miles over lots of years with NO counterweights. A downside to the thicker weights is they will have to be removed if the crankshaft is to be reground at some later date.
PM me or ask on the forum if you have any ?s