0914066 EVINRUDE BACK-UP RING, Manual release

(1) Combustion Chamber
(a) 4D31, 4D31-T, 4D32 The combustion chamber consists of the cylinder head and toroidal pistons, hole type injection nozzles and sheathed type glow plugs being installed in the cylinder head.Combustion occurs when the fuel is directly injected into the combustion chamber with the power operating the piston directly.(b) 4DR5 The combustion chamber is formed by the lobes-shaped main combustion chamber in the piston head and Mitsubishi's own bell-shaped swirl chamber. A chamber jet is press-fitted into the swirl chamber that is made of material with little thermal expansion and good thermal conductivity. Also installed in the chamber are the sheathed glow plug and throttle injection nozzle.The upward movement of the piston during the compression stroke imparts a violent swirling motion to the air charged into the swirl chamber, to which fuel is injected for combustion. As the combustion goes on, the gas moves from the swirl to main combustion chamber where it is mixed with the air present. And further combustion occurs. (c) Water DirectorFor more effective cooling of the combustion chamber, water directors that direct coolant flow are pressed into the bottom of the cylinder head. The 4D3 engine cylinder head has a nozzle water hole provided for higher cooling effect.(2) Valve Mechanism
The valve mechanism is an overhead valve type.(a) Both the inlet and exhaust valves are made of surface-treated heat-resistant steel. The valve seat angle is 45° in both valves. Valve stem seal is mounted to the valve stem, which controls the amount of lubricant on the sliding surfaces between the valve and valve guide.A valve guide with carbon cutter is used for the exhaust side.(b) Two unevenly pitched valve springs are used, the inner and outer with coil directions opposite to each other.(c) The rocker has an induction-hardened surface in contact with the valve cap. A bushing is used in the hole, into which the rocker shaft is fitted. Because of them, wear resistance is improved.(d) The rocker shaft is a hollow round rod with sealing caps at both ends to seal it off. Its inside is an engine oil passage.(e) The push rod has a steel ball welded to its bottom end and a spherical or depressed piece welded to its top end. Both ends are carburized case-hardened. (f) The tappet on the 4D3 is of cylindrical shape, while that on 4DR5 of mushroom-shape. Its mating surface with the camshaft is a large-diameter sphere to prevent local wear.(g) The camshaft is provided with an oil pump drive gear, with its journals, cams, and gear induction-hardened. The cam on 4D3 is a taper cam.(3) Crankcase and Cylinder Sleeve
(a) The crankcase is made of cast iron and built rigid with minimum stress concentration and deformation.(b) Three camshaft bushings are installed in the camshaft bearings of the crankcase. To facilitate insertion and removal of the camshaft from the front end of the crankcase, the bushing I.D. is made smaller toward the rear.(c) On 4D31, 4D31-T and 4DR5 engines, cylinder sleeves are press-fitted into the crankcase.(4) Piston and Piston Ring
(a) Piston The piston, made of aluminum alloy casting, has a strut inside (no strut installed on 4D31-T) that ensures an adequate clearance between the piston and cylinder sleeve.The piston pin arrangement is full-floating. The piston pin is offset toward the thrust side, which, together with the effect of the strut, minimizes piston slap. Stamped on the top surface of the piston are the piston weight mark, part number, oversize mark (oversize piston only) and the front mark On 4D31-T and 4D32, a piston ring insert is cast in the top ring groove for increased durability.(b) Piston Ring There are three or four piston rings installed: two compression rings (three on 4DR5) and one oil ring. Piston rings are shaped as illustrated.(5) Connecting Rod and Connecting Rod Bearing
The connecting rod is a die forging with an I cross section ensuring high rigidity. A lead bronze bushing is press-fitted into its small end, while a split-style plain bearing is used in its big end.An oil passage is provided obliquely through the stem and an oil jet at the small-end to lubricate the small-end bushing and cool the piston (4D3 only). The connecting rod small end of 4D31-T is wedge-shaped.(6) Crankcase and Main Bearing
(a) Crankshaft The crankshaft is a highly-rigid die forging integral with the balance weights. The pins, journals, and rear oil seal sliding surfaces are induction-hardened for improved wear resistance.By means of oil passages drilled through the pins and journals, part of the main bearing lubricating oil is fed to pins for lubrication of the connecting rod bearing. At the front end of the crankshaft, there are a crankshaft pulley and crankshaft gear attached with a nut. The crankshaft pulley drives the alternator and water pump through the V-belt.On some version of 4D31-T, a pulley with damper is installed that absorbs torsional vibration of the crankshaft.The crankshaft gear drives the camshaft and injection pump. (Refer to "Timing Gear".) The flywheel is mounted in the rear of the crankshaft. An oil seal is installed at front and rear of the crankshaft.(b) Main Bearing The main bearing is a split-style plain bearing made of special alloy plated kelmet metal with a steel back. The upper main bearing has an internal oil groove and oil hole which is aligned with the oil hole in the crankshaft.Five pairs of main bearings are used. Split-style thrust plates are mounted with the rear pair of main bearings.(7) Timing Gear
The timing gear are housed in the timing gear case at the front of the engine. Illustration shows the gear train.Each gear is a helical gear machined by a shaving machine to high precision and surface-treated for enhanced durability.A timing mark is stamped on each gear. At reassembly, correct meshing can be achieved by aligning these marks.A bushing is press-fitted into the idler gear which turns on the idler shaft. The oil hole drilled through the idler shaft and gear provides an oil passage for lubrication of bushing and gears. On 4D3 engines, an