Page 68 - Mechanic Diesel - TT

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