Engine: Description and Operation
ENGINEThe engine is water-cooled, in line 4 cylinders, 4 stroke cycle gasoline unit with its DOHC (Double overhead camshaft) valve mechanism arranged for "V" type valve configuration and 16 valves (4 valves/one cylinder).
The double overhead camshaft is mounted over the cylinder head; it is driven from crankshaft through timing chains, and no push rods are provided in the valve train system.
ENGINE LUBRICATION
The oil pump is of a trochoid type, and mounted under the crankshaft. Oil is drawn up through the oil pump strainer and passed through the pump to the oil filter.
The filtered oil flows into 2 paths in cylinder block. In one path, oil reaches the crankshaft journal bearings. Oil from the crankshaft journal bearings is supplied to the connecting rod bearings by means of intersecting passages drilled in the crankshaft, and then injected from the big end of connecting rod to lubricate piston, rings, and cylinder wall.
In other path oil goes up to the cylinder head and lubricates valves and camshafts, etc., after passing through the internal oilway of camshafts.
An oil relief valve is provided on the oil pump. This valve starts relieving oil pressure when the pressure exceeds about 420 kPa (59.7 psi).
CYLINDER BLOCK
The cylinder block is made of cast aluminum alloy and has 4 cylinders arranged in "In-Line".
A cylindrical cast iron sleeve is installed in each cylinder.
CRANKSHAFT AND MAIN BEARINGS
A monoblock crankshaft made of cast iron is supported by 5 main bearings which are of precision insert type. 4 crank pins on the crankshaft are positioned 180° apart.
PISTONS, RINGS, PISTON PINS AND CONNECTING RODS
The piston is cast aluminum alloy, and has two compression rings (top and 2nd rings), and one oil ring.
The outer surface of the top ring is treated with nitriding for improvement in abrasion resistance.
The oil ring consists of two rails and one spacer.
The piston pin is offset 1.0 mm towards the major thrust side.
This allow a gradual change in thrust pressure against the cylinder wall as the piston travels its path.
Pins, made of chromium steel, have a floating fit in the pistons and connecting rods. The connecting rods are made of forged steel, and the rod bearings are of precision insert type.
CYLINDER HEAD, VALVE TRAIN AND HYDRAULIC VALVE LASH ADJUSTERS
Cylinder head are made of cast aluminum alloy and cylinder head has 4 combustion chambers arranged in-line. The combustion chamber is pentroof type and a spark plug is positioned in the center of combustion chamber and between intake ports and exhaust ports.
The double overhead camshafts (intake and exhaust) driven by the crankshaft through the timing chains are mounted on the cylinder head. Each of them has 8 cams and they operate the intake valves and exhaust valves respectively via the hydraulic valve lash adjusters.
Operation Of Hydraulic Valve Lash Adjuster
The hydraulic valve lash adjuster, located between the camshaft and valve stem, is direct acting type. With the engine oil delivered into it from the oil pump, the adjuster operates as follows so as to adjust the valve lash (clearance) to "0" automatically at all time.
1. When the camshaft doesn't push the bucket body, the bucket body is pushed against the cam and the body against the stem by the plunger spring force. In this state, the valve lash is kept to "0". (At "0" valve lash, the oil pressure becomes equal in the chambers "A" and "B", and the check ball closes the passage between these two chambers.)
2. When the cam crest of the camshaft starts pushing the bucket body, the bucket body and plunger are pushed downward and at the same time the body is pushed upward by the counter force from the valve stem. As a result, the chamber "B" is compressed and the pressure rises high. Then the oil in the chamber "B" leaks through the slight clearance between the body and plunger. However, as the compression time is very short, the volume hardly changed and thus the bucket body, plunger and body, substantially as one unit, push down the valve stem to open the valve.
3. When the push of the cam crest of the camshaft against the bucket body is over, the operation as described in above 1 starts again. As the oil pressure in the chamber "B" is lower than that in "A" (for the oil in the chamber "B" under high pressure has leaked gradually in above 2), the oil pressure in the chamber "A" pushes the check ball open to allow the oil to flow from the chamber "A" to chamber "B" till the oil pressure becomes equal between the two chambers.