After reconditioning involving straightening, regrinding, or other operations which may affect weight
distribution of the crankshaft, a dynamic balance check shall be made. Corrections shall be made as
necessary to bring the shaft within the maximum unbalance limit of 0.001 ounce/inch (0.720
Dynamic balance of the crankshaft shall be checked on a two plane balancing machine which will show the
amount of unbalance at each end.
Accurate balancing requires that the crankshaft be held within 0.002 inch (0.05 mm) alignment during the
balancing operation. To secure proper support, at least three points of support (front, middle, and rear
main bearing journals) shall be used.
Excessive speeds will cause the crankshaft to whip, resulting in incorrect balance indications. The speed
of crankshaft rotation shall not exceed 325 rpm during balancing.
Bob-weights are not needed on a V-1 2 crankshaft because the throw indexing provides
inherent balance. Crankshafts may be balanced with or without the crankshaft gear
assembled. When balanced without the gear, compensation shall be made for the gear
keyway slot by adding tolerance wax, equal to the weight of the key, to the keyway slot.
Balance corrections shall be made by drilling holes in the counterweight or snag-grinding on the perimeter
of the counterweights, removing sufficient weight at the proper location to attain balance.
Not more than 2 ounces (56.79) of weight shall be removed by grinding.
Additional holes may be drilled in the counterweight, but this should be limited to no more than six 0.75
inch (19 mm) holes, 2 inches (51 mm) deep in any one counterweight bay. (A counterweight bay consists
of two counterweights at either side of a throw). Maintain at least 0.125 inch (3.18 mm) wall thickness
between the hole and the side of the counterweight when drilling balance holes.
Where the limit of metal removed has been reached, balance may be attained by adding weight at another
location. Lead may be tamped in an existing balancing hole and held in place by a plug welded in place.
All such welds shall be magnetically inspected and must show no cracks.
After balancing, dean the crankshaft in accordance with step (c), above, to remove any grinding dust or
i. Preservation and Storage.
Coat the crankshaft thoroughly with dean preservative oil, MIL-L-21260, and seal it in a dean plastic bag to
The crankshaft must be stored In a vertical position. Allowing the crankshaft to lie flat with
unsupported main bearing journals, may cause misalignment.
Store the crankshaft in a vertical position until ready for installation.