TM 5-4310-393-14E.Adjust.CAUTIONToo small a clearance will damage piston, cylinder head, and valves. Too large aclearance will result in difficult starting.1.Adjusting the Cylinder Head (Bumping) Clearance.a.Crank engine to dead center position.b.Ensure cylinder head surface is free of dirt, carbon, or sealing material residue and place cylinderhead gasket onto cylinder head.c.Use a dial indicator to establish true top dead center of the piston.d.Place a straight edge across the top of the cylinder and measure the distance between the top of thecylinder gasket and the top of the piston with a feeler gauge.e.Ensure that the bumping clearance is between 0.0216/0.0255 inch (0.549/0.648 mm).NOTEGaskets come in various thickness. If you have a choice between two gaskets, it isbest to use the thickest one. Use only one gasket with the required thickness.2.Adjusting the Pushrods.a.Adjust complete pushrod(Figure 5-30, Item 1) so dimension "A", measured frombottom of pushrod to the top of the collar, equals5.8189/5.8268 inch (147.8/148.0 mm). This adjustmentIs required for proper engagement of complete pushrodwith pinion on decompression shaft.3.Adjusting the Tappet Clearance.a.Put decompression lever (1) inSTART position. (Figure 4-3).b.Turn engine clockwise when facingthrottle control lever until compression resistance can befelt.c.Check clearance between rockerand valve stem with a feeler gauge. Tappet clearancecold should be 0.004 Inch (0.10 mm). To correctclearance, loosen nut (2).d.Adjust screw (Figure 5-31, Item 3)with a screwdriver until feeler gauge can be pulledbetween rocker and valve stem with very slightresistance after nut (2) has been tightenedFIGURE 5-30. PUSHRODFIGURE 5-31. TAPPET ADJUSTMENT5-24
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