Most  bore  gauges  consist  of  a  dial  indicator, extension   pieces,   bezel   and   locknut,   spring-loaded guide, and sensor button. Before  you  start  a  measuring  procedure,  expose both the bore gauge and the master ring gauge, or any other tools used to preset the bore gauge, and the part to be  measured  to  the  same  work  place  environment  for one hour. If you fail to do this, a temperature differential may cause your readings to be inaccurate. When you use the bore gauge, touch only its insulated handle. The gauge has two stationary spring-loaded points and an adjustable point to permit a variation in range. These  points  are  evenly  spaced  to  allow  accurate centering of the tool in the bore. A fourth point, the tip of  the  dial  indicator,  is  located  between  the  two stationary points. By simply rocking the tool in the bore, you  can  observe  the  amount  of  variation  on  the  dial. Figure  2-7  shows  a  bore  gauge  inside  a  bore  being moved in a gentle rocking motion. Always follow the bore gauge manufacturer’s operating manual. Measure the  bore  and  mark  the  areas  you  measure.  A  good Figure 2-7.—Measuring a bore with a bore gauge. practice is to check the bore gauge in the standard after you  take  each  set  of  measurements  to  ensure  that readings are accurate. STRAIN/DEFLECTION  GAUGE A  strain  or  deflection  gauge  is  used  to  check  the crankshaft  alignment  on  large  diesel  engines.  It  is  a specially  adapted  dial  indicator  that  fits  between  the crank webs. The strain gauge reads the flexing motion of the webs directly as the crankshaft is slowly rotated (correct   engine   rotation).   The   gauge   dial   reads   in 0.00l-inch  graduations. The strain gauge consists of a dial indicator, contact point,  balancing  attachment,  clamping  nut,  spring plunger, rods and extension, and bezel. Before  you  take  a  reading,  be  sure  the  engine  is completely assembled and cold. Place the strain gauge between  the  webs  of  a  crankthrow,  as  far  as  possible from the axis of the crankpin. The ends of the indicator should rest in the prick-punch marks in the crank webs. If   these   marks   are   not   present,   consult   the manufacturer’s  technical  manual  for  the  proper  location of the marks. Ensure that the strain gauge is at the same temperature  as  the  engine.  A  temperature  differential may cause inaccurate readings. Readings are generally taken  at  the  four  crank  positions;  top  dead  center, inboard,  near  or  at  bottom  dead  center,  and  outboard However, the manufacturer’s technical manual for the specific  engine  provides  information  concerning  the proper  positions  of  the  crank  for  taking  readings.  In some situations, due to the position of the dial, you may need to use a mirror and a flashlight to read the gauge. Once you have placed the indicator in position for the first reading, DO NOT touch the gauge until you have taken and recorded all four readings. Variations in the readings  taken  at  the  four  crank  positions  indicate distortion of the crank, which may be caused by any of several factors, such as a bent crankshaft, worn bearings, or   improper   engine   alignment.   The   manufacturer’s technical manual will provide you with the maximum allowable  deflection.  Figure  2-8  shows  the  locations  for taking crankshaft deflection readings. BORESCOPE A borescope is used to inspect internal parts on an engine without having to disassemble the engine. This instrument helps a great deal in estimating the amount of  repair  work  needed  and  the  time  required  for  the repair. Figure 2-9 shows a typical borescope. 2-5