First, check all equipment to ensure that are correct. 

Second, Check shafts and bearing to ensure that they are level and parallel to each other, replace or rectify if necessary.

Third, By a spirit level and adjustable comparator bar or micrometer rectify any parallelism error present and mark a permanent datum lines for the adjustable shafts.

Fourth, Place respective sprockets and shafts in approximate alignment and fit the keys in accordance with correct engineering practice. Do not finally secure keys at this stage.

Fifth, Take care with the sprocket of split design, it must perfect abutting of the faces of each half, Proceed with the key fitting after the halves are finally bolted together, otherwise the key can prevent correct assembly and subsequently result in Malingering.