Before you reinstall a good camshaft, remove the minor surface defects on the cams and the camshaft by using crocus cloth or a fine stone. INSPECTING, MAINTAINING, AND REPLACING PISTON RINGS AND PISTONS The  following  paragraphs  are  general  procedures for  inspections,  maintenance,  and  replacement  of  piston rings and pistons. You must consult the manufacturer’s technical manual for specific instructions. PISTON RINGS Over a period of time all piston rings wear. Some stick and may even break. While you may be able to free stuck   rings   and   make   them   serviceable,   you   must replace excessively worn or broken rings with new ones. The  installation  of  a  new  set  of  rings  in  an  engine requires  great  care.  Most  of  the  damage  that  is  done occurs when the rings are being placed in the grooves of a piston or when the piston is being inserted into the cylinder  bore. Be  very  careful  when  you  remove  the  piston  and connecting rod from the cylinder. In most engines, you should not remove a piston from a cylinder until you have scraped the cylinder surface above the ring travel area.  In  addition  to  removing  all  carbon,  you  must remove  any  appreciable  ridge  before  removing  the piston. Do not remove a ridge by grinding, as this will allow small abrasive particles from the stone to enter the engine.  Use  a  metal  scraper  and  place  a  cloth  in  the cylinder  to  catch  all  metal  cuttings.  You  can  usually scrape enough from the lip of a cylinder to allow the piston assembly to slide out of the liner. After removing the piston, you can make a more detailed inspection of the ridge. Finish scraping the remaining ridge, but be careful not to go too deep. Finish the surface with a handstone. For large ridges, you may need to remove the liner and use a small power grinder. With  the  piston  and  connecting  rod  removed,  check the condition and wear of the piston pin bushing, both in the piston and in the connecting rod. The best way to remove and install piston rings is with a tool similar to that shown in figure 3-19. These tools generally have a device that limits the amount the ring can be spread and prevents the rings from being deformed or broken. A  ring  that  is  securely  stuck  in  the  groove  will require additional work. You may need to soak the piston Figure 3-19.–Piston ring tools used for removal or installation. overnight in an approved cleaning solvent or in diesel oil. If soaking does not free the ring, you must drive it out  with  a  brass  drift.  The  end  of  the  drift  should  be shaped and ground to permit its use without damage to the lands. After  removing  the  rings,  thoroughly  clean  the piston with special attention to the ring grooves. (Diesel oil  or  kerosene  are  satisfactory  cleaning  agents.)  In addition, you may need to clean excessive deposits from the oil return holes in the bottom of the oil control ring grooves with a twist drill of a diameter corresponding to the original size of the holes. Make  another  complete  inspection  after  cleaning the  piston.  Check  all  parts  for  any  defects  that  could require   replacement   of   the   piston.   Give   particular attention to the ring grooves, especially if the pistons have been in service for a long period of time. A certain amount of enlargement of the width of the grooves is normal, and SHOULDERING of the groove may occur. Shouldering, as illustrated in figure 3-20, results from the  “hammering  out”  motion  of  the  rings.  The  radial depth  of  thickness  of  the  ring  is  much  less  than  the groove depth, and while the ring wears away an amount of metal corresponding to its own width, the metal at the bottom of the groove remains unchanged. Shouldering 3-14