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Chapter 3 Internal Combustion Engines
Repairing the Engine Frame or Block

Engineman 2 - Intermediate engine mechanics training manual
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Measure the bore in the cylinder block, with a dial indicating   bore   gauge,   to   determine   if   wear   or   an out-of-round   condition   exceeds   the   manufacturer’s specification.  Figure  3-2  illustrates  the  use  of  a  bore gauge to measure a cylinder bore. You can use an inside micrometer as well, but a dial indicating bore gauge is easier to use. Inspect and measure the engine block’s hold-down bolt holes. Use a telescoping snap gauge to determine if wear  has  caused  enlargement  of  the  holes.  If  a telescoping snap gauge is not available, try to move each bolt from side to side with your fingers. If a bolt moves from  side  to  side,  its  hole  has  enlarged  and  must  be repaired.  Always  follow  the  manufacturer’s  instructions on how to correct a hole enlargement problem. DYE PENETRANT TEST Conduct  a  preliminary  dye  penetrant  test  on  the engine block’s surface to identify cracks that you cannot see  otherwise.  Be  sure  to  follow  the  manufacturer’s instructions  on  how  to  conduct  this  test.  Remember  that only  a  certified  nondestructive  testing  technician  can perform a dye penetrant test that meets the requirements of  quality  assurance. AIR AND WATER PRESSURE TESTS Test  the  cylinder  block  for  cracks  in  the  cylinder bores between the water jacket and the oil passages by using either air pressure or water pressure. The purpose of each test is to pressurize the water Jacket to the point, within  safe  limits,  that  leaks  show. Figure 3-2.—Checking the cylinder bore for wear or out-of-roundness. Air Pressure Test Before you perform the air pressure test, make sure you completely strip and clean the block. Then, follow these  basic  procedures: 1.   Seal all of the block’s freshwater passages with gaskets and flanges. 2. Connect a low-pressure air hose to a fixture on one of the flanges. 3.   Immerse the block into a tank of water heated to the engine’s normal operating temperature. Allow the engine to soak for approximately 20 to 40 minutes, as specified by the manufacturer. This allows the block to warm to the temperature of the water. 4.  Apply  approximately  40  psi  of  pressure  to  the block and watch for bubbles. Bubbles indicate a crack or leak in the block. Determine what repair is needed or can  be  made  when  you  identify  the  source  of  the bubbles. If you cannot dip the block, you may still perform the air pressure test. Attach the hose to a fixture secured to an opening to the water jacket. Pressurize the water jacket. Carefully spray soapy water over the block and look for air bubbles caused by the pressurized air. Water Pressure Test The water pressure test is similar to the air pressure test,  except  that  defects  are  indicated  by  water  leaks rather than by air leaks. Before you perform the water pressure  test,  strip  and  clean  the  block  Then,  follow these  procedures: 1. Seal off all but one of the freshwater openings with flanges and gaskets. Make seals airtight. 2.   Fill the water jacket with fresh water until all air is purged from the water jacket. Seal the fill opening with a flange that contains an air hose coupling. 3.  Attach  an  air  hose  and  pressurize  the  water jacket to approximately 40 psi (see the manufacturer’s manual). Maintain the pressure in the water jacket for at least 2 hours. 4.   Inspect the cylinder bores, air box, oil passages, crankcase, and cylinder block exterior for the presence of water. The presence of water at any of these locations indicates that the water jacket has one or more defects. 3-2







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