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14
12
13
15
4
d = 0,8 ÷1,0 d =1,3
Checks and overhaul
After prolonged running of the engine the hammering of the
valves on their seats at high temperature tends to harden the
faces of the seats and makes manual grinding difcult. It is
necessary to remove the hardened surface with a 45° cutter (g.
12).
Grinding of valve seats causes a widening of the valve seat face
P (g.13).
Final lapping of the valve on the seat must be carried out by
coating the seat with a ne lapping compound and rotating the
valve in a clockwise and counterclockwise direction with slight
pressure until a perfect surface nish is obtained (g.14).
Observe the valve seating clearances indicated in the following
table (g.10).
Fitting mm Max. wear mm
Important
• In the case of lower values the valve may strike the piston. In
the case of values in excess of 1.3 mm the valve seat rings must
be replaced.
Fitting of new seats or valves always requires preparatory
grinding. Valves are available with the external diameter
increased by 0.5 mm.
After grinding wash the valve and seat carefully with petrol or
parafn in order to remove residual grinding paste and chips.
Once you have nished grinding check the efciency of the seal
between the valve and seat as outlined below:
1. Fit the valve on the head with spring, washers and split
cones (g.9).
2. Invert the head and pour in a few drops of diesel fuel or oil
around the edges of the valve head.
3. Blow compressed air into the inlet of the cylinder head
taking care to seal the edges so that the air does not escape
(g.15).
Should air bubbles form between the seat and the valve remove
the valve and regrind the seat.
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