GMC T Series 1994 Repair Manual page 344

• Valve face for grooving. If the groove is so deep
that re-facing would result in a knife edge margin,
the valve must be replaced.
• The valve face may be reground to specifications
if it is otherwise in good condition. If the valve
face cannot be ground within the limits given, it
must be replaced.
• Lightly lap the reconditioned valves into the valve
seat.
Valve Grinding
• Follow the grinder manufacturer's instructions.
• Grind all faces to 45°.
Inspect
• Each valve face carefully.
- Re-grind if necessary.
• Valve margin for minimum thickness.
- 0.9 mm (0.031 in.) minimum, if margin is
thinner, replace valve.
Valve Replacement
Tools Required:
J 38847, J 38848 and J 38849 Valve Reamer
Sets
• When replacing valves, valve seats must be
reconditioned, refer to " Valve Seat Service" in
this section.
• Measure valve to be replaced and select an
oversize (O.S.) service valve.
- 0.075 mm O.S.
- 0.150 mm O.S.
- 0.300 mm O.S.
• Select the reamer set for your valve(s).
- 0.075 mm O.S. valve, use J 38847.
- 0.150 mm O.S. valve, use
- 0.300 mm O.S. valve, use J 38849.
• Refer to " Reaming Valve Guides" in this section.
VALVE SEAT SERVICE
Important
Valve guides must be reconditioned prior to
servicing valve seats. Refer to " Valve Guide
Service" in this section.
If the seats are reconditioned, the valves also must
be reconditioned or replaced, refer to " Valve
Service" in this section.
I * Inspect
• Valve seats for excessive wear and burned spots.
Seat Grinding
Valve seats may be reconditioned by grinding.
An oscillating type valve seat grinder is preferred.
Follow the grinder manufacturer's instructions.
Grind all valve seats to a 46° angle.
38848.
J
• After adjusting valve seat width or contact line, be
VALVE SPRING SERVICE
| y | Inspect
Figure 39 - Valve Wear
Valve face to seat
reconditioned or new valve.
Seat width.
- If the contact line is too high, it can be
lowered using a 30° stone.
- If the contact line is too low, it can be raised
using the 45° stone.
- If the seat is too narrow, it can be widened
using a 45° stone.
- If the seat is too wide, it can be narrowed
using a 60° stone.
sure to recheck Steps 1 and 2 above.
Tools Required:
J 9666 Valve Spring Tester
J 8062 Valve Spring Compressor
Valve springs.
- Spring tension, refer to Figure 40. If below
specification, replace.
Valve spring seating surfaces for wear or gouging,
replace as required.
contact line using a