The latest revision of Lycoming Service Instruction No. 1012 provides information on the location and assembly procedure for counterweights on each Lycoming crankshaft equipped with counterweights. The illustrations and engine listing in this service instruction show that some crankshafts may have two or more counterweights of the same part number attached to the crankshaft with rollers having unlike part numbers.
This can be a little confusing, and we have had reports from mechanics who assembled an engine using two different-size rollers (two different part numbers) in the same counterweight. Another report had the mechanic identifying the rollers by the size of the part number lettering rather than reading and comparing the part numbers. Fortunately, in the cases we are aware of, the error was corrected before assembly of the engine continued.
To help in clearing up this possible source of confusion, it should be remembered that each counterweight is installed with two identical rollers. The rollers will have the same part number and will be the same size. The next counterweight on the same crankshaft may use rollers of a different size and part number, but these two rollers will also be identical in size.
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Service Instruction No. 1012
For more information on the installation of counterweight rollers, refer to the related service publication on this subject.