3AD-06864-0 Tohatsu BOLT, 6 - 25 PRE-COATED

Illustration 1 g01122516
Air flow through the engine
(1) Exhaust outlet
(2) Air inlet
(3) Turbocharger
(4) Air cleaner
(5) Exhaust manifold
(6) Exhaust valves
(7) Inlet valves
(8) Sea water inlet to aftercooler
(9) Sea water outlet from aftercooler
(10) Aftercooler
(11) Cylinder headClean inlet air from the air cleaner (4) is pulled through the air inlet of the turbocharger (3) by the turning of the compressor wheel. The compressor wheel causes a compression of the air. The turbocharger compresses the inlet air so that a larger volume of air can be drawn into the cylinders. This compressing of the inlet air is referred to as boost. The compression of the inlet air causes the temperature of the air to increase. The air then flows to the aftercooler (10). The aftercooler utilized cool sea water to cool the inlet air. Cooling of the inlet air causes the air to become more dense. This increases the combustion efficiency and the horsepower output of the engine. The air then flows from the aftercooler to the inlet manifold of the engine. When the inlet valves (7) open, the air flows into the engine cylinders. The air is mixed with the fuel for combustion. When the exhaust valve opens (6), the exhaust gases go out of the engine cylinders and into exhaust manifold (5). From the exhaust manifold, the exhaust gases flow through the blades of the turbine wheel in the turbocharger (3). This action causes the turbine wheel to spin. The exhaust gases then flow out of exhaust outlet (1) of the turbocharger.Turbocharger
Two turbochargers are mounted on the rear of the engine. All the exhaust gas from the left exhaust manifold goes through the left turbocharger, and the right turbocharger uses the exhaust from the right exhaust manifold.
Illustration 2 g01385582
Turbocharger
(12) Air inlet
(13) Compressor housing
(14) Compressor wheel
(15) Bearing
(16) Oil Inlet port
(17) Bearing
(18) Turbine housing
(19) Turbine wheel
(20) Exhaust outlet
(21) Oil outlet port
(22) Exhaust inletAll the air that enters the engine passes through the turbocharger. All the exhaust gases from the engine pass through the turbocharger.The exhaust gases enter turbine housing (18) through exhaust inlet (22). The exhaust gas pushes the blades of the turbine wheel (19). The turbine wheel is connected by a shaft to the compressor wheel (14).Air that passes through the air filters enters the compressor housing air inlet (12) by the rotation of compressor wheel (14). The compressor wheel causes the inlet air to be pushed into the inlet side of the engine. Boost pressure is caused when the compressor wheel pushes more air into the inlet side of the engine. This results in an inlet manifold pressure that exceeds atmospheric pressure. This allows the engine to burn more fuel. When the engine burns more fuel the engine produces more power.When the throttle is opened, more fuel is injected into the cylinders. The combustion of this additional fuel produces greater exhaust temperature. The additional exhaust temperature causes the turbine and the compressor wheels of the turbocharger to turn faster. As the compressor wheel turns faster, more air is forced into the cylinders. The increased flow of air gives the engine more power by allowing the engine to burn the additional fuel with greater efficiency.Bearings (15) and (17) for the turbocharger use engine oil under pressure for lubrication and cooling. The oil comes in through oil inlet port (16). The oil then goes through passages in the center section to lubricate the bearings. This oil also cools the bearings. Oil from the turbocharger goes out through oil outlet port (21) in the bottom of the center section. The oil then goes back to the engine oil pan.Aftercooler
The C32 has a SCAC aftercooler. The aftercooler is installed above the inlet manifold.
Illustration 3 g06280476
Air inlet system
(23) Turbocharger
(24) Aftercooler
(25) Elbow on the front bonnet of the oil coolerThe inlet air from the compressor side of the turbocharger flows into the aftercooler. The air passes through the core assembly which lowers the temperature as much as 38°C to 93°C (100°F to 200°F). The cooler air flows out of the bottom of the aftercooler and into the air chamber. The cooler air then flows through the inlet ports (passages) in the cylinder heads. Cooling the inlet air causes the air to become more dense. Dense air will help the engine burn the fuel more efficiently. This action gives the engine more power.Valve System Components
Illustration 4 g01385586
Valve system components
(26) Rocker arm
(27) Locknut
(28) Rocker arm shaft
(29) Camshaft
(30) Valve bridgeThe valve train controls the flow of inlet air and exhaust gases into the cylinders and out of the cylinders during engine operation. The camshaft (29) controls the timing of the valves during engine operation.The crankshaft gear drives the camshaft gear through an idler gear. The camshaft must be timed to the crankshaft to get the correct relation between the piston position and the valve position.The camshaft has three camshaft lobes for each cylinder. One camshaft lobe operates the inlet valves. One camshaft lobe operates the exhaust valves. One camshaft lobe operates the unit injector. The camshaft lobes cause the follower on the rocker arm to actuate the valves and the unit injector.Each cylinder has two inlet valves and two exhaust valves. Valve springs hold the valves closed and the valve springs resist the opening of the valves. This action ensures that the valves will close at high rpm and under high boost pressures. Valve rotators cause the valves to rotate while the engine is running. The rotation of the valves prevents the valves from burning by constantly changing the contact area of the valve face and the valve seat. This rotation gives the valves longer service life.