TM 5-3895-374-24-2 Installation/ Tensioning V-Drives Installing A Drive Here   are   a   few   suggestions   to   keep   in   mind   when installing the drive: 1. Use a matched set of belts. 2. Clean oil and grease from the sheaves; remove any rust or burrs from the sheave grooves. 3. Shorten   the   center   distance   of   the   drive   until   the belts can be put on the sheaves without forcing. 4. Make  sure  that  the  sheaves  are  correctly  aligned, that the shafts are parallel, that there is clearance for the drive to run and that the bearings have oil. 5. Work belts around in the groove by hand, so that the slack of all belts is on the top, or slack of all belts is on the bottom. Do  not  apply  with  the  slack  of  some  belts  on  the bottom (see solid line) and the slack of others on the top  (see  dotted  line).    Since  V-belts  will  not  slide  in the  groove,  belts  thus  applied  will  be  injured  when tightened for operation. Now tension the drive until only a slight bow appears on    the    slack    side    of    the    belts    when    they    are operating. 6. In a day or so, when the belts have had time to seat in the grooves, re-tension the belts. All  V-belt  drives  should  be  guarded  in  much a   manner   as   to   comply   with   the   Williams- Steiger  Occupational-Safety   and   Health   Act and  with  all    state  and  local  laws   and   the American  National  Standard  Institute  (ANSI) Safety code. Tensioning The Drive General Rules of Tensioning: 1. Ideal tension is the lowest tension at which the belt will not slip under peak load conditions. 2. Check tension frequently during the first 24-48 hours of run-in operation. 3. Over tensioning shortens belt and bearing life. 4. Keep belts free from foreign material which  may  cause slip. 5. Make  V-drive  inspection  on  a  periodic  basis.    Tension when slipping. Test The Tension If you want to check the tension in a conventional V-belt drive, use the procedure below: 1. Measure the span length, t. 2. At the center of the span (t) apply a force (perpendicular to  the  span)  large  enough  to  deflect  the  belt  1/64"  for every inch  of  span  length.    For  example,  the  deflection of a 100 inch span would be 100/64 or 1 9/16 inches. 3. Compare  the  force  you  have  applied  with  the  values given in Table 12.  If the force is between the values for normal   tension,   and   1-1/2   times   normal   tension,   the drive tension should be satisfactory.  A force below the value  for  normal  tension  indicates  an  under  tensioned drive.    If  the  force  exceeds  the  value  for  1-1/2  times normal  tension,  the  drive  is  tighter  than  it  needs  to  be. A   new   drive   can   be   tightened   initially   to   two   times normal  tension  to  allow  for  the  normal  drop  in  tension during run in. Installation and Take-up Allowance After calculating a center distance from a standard pitch length, make provision for adjusting the center distance as   in   Table   13,   to   allow   for   installation   of   the   belts without  injury,  for  tensioning,  and  for  maintenance  of proper tension throughout the life of the belt. page 3 - 688