Page 68 - Mechanic Diesel - TT
P. 68

MECHANIC DIESEL - CITS




           Valve Guide Service

           •  Valve guides are checked for wear
           •   Wear in a bell mouth fashion
           •   Can result in oil consumption
           •   Valve seat has worn and is wider than usual

           •   Look for a worn valve guide as the cause
           •   Checking valve stem-to-guide clearance
           •   Split ball gauge and micrometer
           •   Dial indicator
           Guide Repair

           •  Guides are repaired in several ways
           •   Worn integral guide bored out to accept a pressed-fit insert guide
           •  Worn insert guide pressed out and replaced with a new one
           •   Knurling
           •   Thin wall insert

           Grinding Valves
           •  Valves are refinished on face angle using a valve grinder
           •   Stem tip is reground flat
           •   Grinding wheel is dressed with an industrial diamond
           •   Some machinists grind an interference angle

           •   Very little metal is removed from surface of the valve face
           Grinding Valve Seats
           •  Valve guides must be refinished before refinishing valve seats
           •   Valve seats are refinished with a grinding stone or a seat cutter

           •   45-degree seat angle that mates with valve face is machined until seat area is clean and free of pits
           •   60-degree angle in the bottom of the seat (i.e., throat angle) is cut very lightly
           •   Head must be thoroughly cleaned of all grit before beginning assembly
           Checking Valve Stem Installed Height
           •  Seat and valve are reground
           •   Stem moves further into the cylinder head

           •   Results in increased valve stem tip height and valve spring installed height
           •   After grinding the valve and seat
           •   Check installed height
           •   Shims may be installed under the springs when a head reassembled

           Solvent Testing the Valve and Seat
           •  After the valve and seat have been ground:
           •   Install the spark plugs in their holes
           •   Turn head over so combustion chamber faces up





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 CITS : Automotive - Mechanic Diesel - Lesson 11 - 14  CITS : Automotive - Mechanic Diesel - Lesson 11 - 14
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