I brought one that was .006 out to Ed's Crankshafts in Hayward. They do lots of dragster engines and antique crankshafts for Packards, Lincolns, Locomobiles, and of course, Model A's. They gave it back perfect. The car runs a smooth as a sewing machine now.
As George has pointed out, I can deflect an A crankshaft on a pair of Vee-blocks by 0.002 just by pressing downwards on it with my arms (I guess about 40 lbs of pressure or so). It doesn't take much! And the T cranks are even worse...
Oh, one other thing: Never, ever trust the 60 deg. machine centers on an A crankshaft. Nevermind what various regrinds may or may not have done, frequently the factory machining centers were lost during the various straightening processes that the crank went through at the factory! It went through several, and at some point in the manufacture, it became more efficient to indicate the centerline off the OD of the mains than off the original 60 deg centers. Think about it...it makes alot of sense. I have a friend, who always wishes to work off machine centers when grinding a crankshaft, but this requires that he re-cut the original 60s in order to true them. That requires some very good machining skills. The key, when approaching any crankshaft, is that the absolute center of the crank axis be established off the absolute center of the flywheel flange. Happy Motoring!
The "A" crank is very flexible, it moves around in operation, it also can move when it is being ground, and many cranks are "straightened" because they seem to be bent on Vee blocke, but it is just wear, a used crank that seems to have .007 runout on V blocks can be within .002 when checked on the unworn areas near the radius.
The center main wears on the opposite side of the front and rear main journals ---many times a straight but worn crankshaft is "straightened" to recenter the crankshaft on the worn journals ---then it is ground, that crankshaft will have flywheel flange runout unless that is also corrected ---the timing gear shoulder is forgotten, the new centerline changes the balance ---
If the worn crankshaft is ground with too much pressure on the steady rest the center main will be ground off center --it's possible your crank is not bent, just ground off center.
