Section XVI 14-80   General. The pistons are tin-plated aluminum alloy and are precision machined, cam ground and balanced. Each piston is fitted with a nickel alloy top ring insert. Three compression rings and one oil control ring are located above the piston pin. The top compression ring and the two scraper segments of the three-piece oil rings are chrome plated, Holes drilled through the walls of each piston at the oil ring groove allow excess oil collected in the groove to return to the oil pan. Pistons are the full floating type, held in the piston by retainer rings. A connecting rod and bearing connects each piston to the crankshaft. 14-81  Piston,  Rod,  and  Rod  Bearing  Removal  and  Disas- sembly. a. Syptoms and Isolation Of Malfunction.  A  mal- function of a component of the piston assembly is usually indicated by loss of engine power, increased oil consump- tion, bluish-white exhaust smoke, excessive engine knock, or low oil pressure. b.  Removal  and  Disassembly. (1)  Remove  engine  assembly.  (para.  2-13). (2)  Support  engine  on  block  or  engine  stand. (3)  Remove  cylinder  head  (para.  14-77). (4) Drain engine oil, and remove the oil pan, oil pump and discharge tube (para. 14-65). (5)  Remove  the  piston  ring  travel  ridge  from  the cylinder  sleeve.  (para.  14-85). (6)  Remove  the  lock  bolts  securing  the  connect- ing rod bearing caps. (See fig. 14-4 1). Remove the bear- ing caps and free the lower end of the rods from the crank- shaft. Remove the shells from the bearing. (7)  Carefully  remove  each  piston  and  rod assembly by pushing the assembly out through the top of the cylinder sleeve. (8) Remove the pin retainer from the groove in the piston at each end of the piston pin. (9)  Remove  the  rings  from  each  piston. Whenever  a  connecting  rod  with  the  piston  is secured  in  a  vise,  be  extremely  careful  that  the bottom  of  the  piston  skirt  is  not  nicked.  Use lead  jaw  protectors  to  protect  the  bottom  of  the skirt  from  the  nicks  and  to  prevent  nicks  in  the rod  which  will  lead  to  piston  and/or  connecting rod   failure. PISTON  AND  RINGS (10) Drive the piston pin from the piston. Immerse  piston  in  180°F  water  for  approximately  5 utes. Remove pin while piston is still hot. NOTE min- The bore in an aluminum alloy piston expands as the piston heats but provides a tight fit between pin and piston at room temperature. 14-82  Piston  Assembly  Inspection  and  Repair. a.  Clean  pistons  with  cleaning  solvent,  Federal Specification P-D-680, and dry them with clean, com- pressed air. After cleaning, the piston skirt, piston rings, and ring grooves should be thoroughly inspected. Be sum oil drain holes in the oil ring grooves are open and clean. If the cleaning solution does not remove all carbon from the bottom of the ring grooves, break the old rings in half and use the butt ends as scrapers. Be careful to remove only carbon or foreign material; do not scrape away any metal from the side or bottom of the ring grooves. b. The piston skirt should be examined for score marks or other indications of improper piston clearance. Inspect the inside of pistons for cracks; scored or cracked pistons should be replaced. Check pistons for wear. The skirt diameter of a new piston is 4.246-4.247 inches (measured at right angles to piston pin and bottom of the skirt); the inside diameter of a new cylinder sleeve is 4.2495-4.251 inches. giving a running clearance of 0.0025-0.005   inch. c.  Any  deviation  from  these  measurements  will indicate the amount of wear on the piston and/or the cylin- der sleeve. If the piston assembly and piston rings are removed from the cylinder sleeve, even after a short period of operation, do not reinstall the same rings; in most cases, used rings will not again seat properly. The outer diameter of new piston rings have tool marks and reasonably rough surfaces which allow for fast wear-in and seating of the rings to the cylinder walls. After a period of operation, the rings wear or lap themselves to fit perfectly with the cylinder’ walls and ring seat. d. If the wear the in piston compression ring grooves does not create side clearance with new piston rings greater than 0.011 inch, if piston pin bore does not exceed 1.5026 inches, and if no cracks or scores are detected in piston pin bosses, on the skirt or in the com- bustion chamber rues, the pistons may be reused with a reasonable life expectancy of one-half to three-fourths that of new pistons. e. Inspect the bore of connecting rod with cap in place and the socket head capscrews tightened to 80 to 85 foot-pounds or the 12 point capscrews tightened to 65 to 65.5 foot-pounds. Using an inside micrometer, measure dimensions A and B as shown in figure 14-43. Record dimensions A and B and arrive at an average dimension. The average dimension must not exceed 2.9705 inches. Subtract dimensions A and B and the remainder must not exceed 0.0015 inch, which is the maximum allowable out- of-roundness. 14-88   Change   12