Engine body Replacement of valve seat Grinding of valves and valve seats 1. Use a valve spring tensioner and dismantle the valve lock. Remove the valve spring washers, springs and aloes. Place the parts in the correct order in a valve rack. Remove the valve stem seals. 2. Clean the parts. Fig. 17. A = distance between cylinder head plane and valves. The valve seat should be replaced when the distance "A" in Fig. 17 measured with a new valve exceeds 1.8 mm (.0708"). 1. Remove the old valve seat by heating it up with a gas jet (600-700°C / 1112-1292°F) diagonally over the seat. Allow the cylinder head to cool approx. 3-5 minu- tes in the air.
Carefully tap out the seat with mandrel (check that the cylinder head is not dama- ged). Fig. 18. Checking of valve spindle wear Diameter mm: I nlet Outlet MD2010, MD2020 5.90 mm 5.90 mm (.2322 in) (.2322 in) MD2030, MD2040 6.89 mm 6.84 mm (.2712 in) (.2692 in) Alternatively the valve seat can be milled out (check that the cylinder head is not damaged). Check the wear on the valve spindle. Measure the diameter with a micrometer at points I, II and III as per Fig. 18. ' 2. Clean the seat housing in the cylinder head care- fully. Check the head for cracking. 3. Cool down the new seat with liquid nitrogen or the li ke to minus 60-70°C (140-158°F) and heat up the cylinder head to approx.
60-100°C (140-212°F). 4. Press the seat in the head. Use a hydraulic press (1000-1500 kp / 2204-3307 lbf) and suitable mandrel. 5. Work the seats to the correct angle and width. Fig. 19. Valve disc edge 4. Grind the valves in a valve grinding machine Grind the sealing surface as little as possible, just so that it is "clean". If the the valve disc edge after grinding is less than 0.5 mm (.019 in) the valve should be scrapped (see Fig. 19). The same ap- plies to valves with crooked valve spindles. 28