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Valves, valve seats
Grinding valves
Before grinding, check the valve guides for wear.
Replace worn guides and ream.
Machine the valves if the sealing surfaces are damaged.
Both inlet and exhaust valves should have a contact
surface that is 1/2
°
smaller than the valve seat contact
surface. The smaller contact surface gives better seal-
ing with a newly ground valve. The surface difference
disappears after a time to get a larger surface for heat
transmission.
Grind the valve sealing surface as little as possible, just
enough to clean the valve.
Valve seats
Grind the valve seat with a grinding machine. Use the
self-centerer that is fitted in the valve guide. Do not
grind off too much material. It is essential that the con-
tact angle is correct and that the surface is even.
Valve seats are available in standard size and oversize.
The outer diameter on an oversize is 0.2 mm greater
than that on a standard size. They are used when grind-
ing valve seat recesses.
Usually valve seat damage is quite insignificant. This
means that normally it is not necessary to reduce seat
width when grinding. Otherwise the grinding is limited
to the measurements that apply to max. distance from
the top side of the valve disc to the cylinder head con-
tact face.
Replace the valves if the valve disc edge is less than:
– inlet valve .................................................. 2.4 mm
– exhaust valve ............................................. 1.7 mm
Replace a valve if the stem is bent.
Exhaust valve
Inlet valve
The valve seat should be renewed when the distance A,
measured with a new valve, exceeds:
Exhaust
2.5 mm
Inlet
1.5 mm
