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Valve guides: verification > < Checking camshaft axial clearance

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Machining valve seats
Machining valve seats
Special tools and workshop equipment required
t  Depth gauge
t  Valve seat re-facing tool
  Note
t  When repairing engines with non airtight valves, it is not enough to reface or to replace the valve seats and the valves. Particularly on high mileage engines, it is necessary also to check valve guides for wear → Chapter.
t  The valve seats should only be reworked just enough to produce a good seating pattern. Before re-facing, the max. allowable re-facing value must be calculated. If the reworking dimension is exceeded, the hydraulic valve clearance compensation can no longer be guaranteed and the cylinder head must be renewed.
The max. permissible reworking dimension is calculated as follows:
–  Insert valve and press firmly against valve seat.
  Note
If the valve is to be renewed as part of a repair, use a new valve for the calculation.
   
–  Measure distance between end of valve stem and upper edge of cylinder head.
–  Calculate maximum permissible reworking dimension from measured distance and minimum dimension.
Minimum dimension: Inlet valve 7.6 mm, Outlet valve 7.6 mm
Measured distance minus minimum dimension = max. permissible reworking dimension.
Example:
  N15-0660

-		Distance measured

Minimum distance		8,0

7,6		mm

mm
=max. perm. rework dimension → Remark0,4mm

1)  The max. permissible reworking dimension is shown on illustrations for reworking valve seats as dimension „b“.
   
Reworking the intake valve seat
  N15-0096
a
b
c
Z
α
β
γ		= Ø 28.7 mm
= Max. permissible reworking dimension 1
= 1.5 ... 1.8 mm
= lower edge of cylinder head
= 45° valve seat angle
= 30° higher angle of correction
= 60° lower angle of correction

2)  Calculating max. permissible reworking dimension → Chapter.
Reworking the exhaust valve seat
   
a
b
c
Z
α
β
γ		= Ø 25.0 mm
= maximum permitted reworking dimension 1
= approx. 1.8 mm
= cylinder head lower edge
= 45° valve seat angle
= 30° upper correction angle
= 60° lower correction angle

3)  Calculating max. permissible reworking dimension → Chapter.
   

Valve guides: verification > < Checking camshaft axial clearance