Engine body 5. Check the wear on the valve guides (see "Check- i ng of valve guides") before the valve seats are treated. 8. Fit the seals, valves, valve springs, spring washers, valve lock and valve caps. See "Assembly of cylin- der head" on page 31. 150 ° Checking of valve guides* Fig. 20. Grinding of valve seat Fig. 22. Clearance, valve - valve guide (cylinder head) A= Max. 2.5 mm (.0984 in) 6. Ream or grind the valve seats (Fig. 20). Grind of Calculate the clearance between the valve spindle and valve guide. j ust enough material so that the valve seat has the right shape and a good mating surface. Wear tolerances: I nlet valve, max. clearance 0.20 mm (.0078 in) Outlet valve, max.
clearance 0.25 mm (.0098 in) lo w k .A " Note: Since the valve guides are treated directly in the cylin- der head this must be replaced when the clearance is exces- sive, even when the valve is new. Fig. 21. Checking of valve seat Replace the valve seat when the distance "A" in Fig. 21, measured with a new valve, exceeds 1.8 mm (.0708 in). For replacement of the valve seat (inlet) see previous page. New seats are grind down so that the distance be- t ween the cylinder head plane and the valve disc surface "A" is: MD2O10, MD2020: 0.70-0.90 mm (.0275-.0354 in) MD2030, MD2040 : 0.85-1.15 mm (.0334-.0452 in) 7. Grind in the valves with grinding paste and check the contact with marker dye. 29