Constructive osobennostia

The engine used valve distribution mechanism with hydraulic tappets and overhead camshaft driven by a toothed belt from the crankshaft pulley. Belt tension is adjusted semi-roller device. Details of the mechanism shown in Fig. 3.11.

The cylinder head (Fig. 3.12) is cast from an aluminum alloy. Valve seats, valve guides and vortex chamber type Recardo Comet V pressed to the head. The nominal height of the cylinder head 116,6-117,0 mm. Maximum surface flatness coupling head to the cylinder block 0,1 mm. The diameter of the holes for the camshaft bearing 30,000-30,021 mm. The diameter of the holes for valve guides: nominal 10.075 mm, repair 11,185-11,196 mm.

Valve guides are made of cast iron and pressed from above the cylinder head. The outer diameter of the sleeves: 11,023-11,034 mm nominal, repair 11,223-11,234 mm. The inner diameter of 7,000-7,015 mm.

Valve seats are made of steel and pressed into the cylinder head. Parameters chamfers valve seat are shown in Table. 3.6.

Table 3.6 Dimensions of facets of saddles of valves

Each intake and exhaust valve has two (external and internal) of the spring. Springs intake and exhaust valves are the same.

Characteristics of the valve springs shown in Table. 3.7.

Table 3.7 Characteristics of valve springs

Hydraulic valve lifters. Pusher free wheeling: nominal 0,023-0,059 mm, the maximum allowable 0.1 mm.

The valves are made of special steel, mounted in a row on the cylinder vertically. Actuated cam camshaft via hydraulic tappets, therefore adjustment of backlashes in a drive is not required.

Characteristics of valves are shown in Table. 3.8.

Table 3.8 Dimensions of valves

Cylinder head gasket made of synthetic material with metal inserts around the cylinders. When installing the gasket tag ?�TOP?� must be addressed to the cylinder head.

Issued gasket four sizes in thickness depending on the piston projection to the surface of the cylinder. The thickness of the marked notches on the edge of the pads (tab. 3.9).

Table 3.9 The thickness of the cylinder head gasket

A camshaft made of cast iron, and has eight cams rotates in five bearings formed by the cylinder head and a removable cover. The permissible axial backlash of a camshaft 0,115-0,188 mm. Height of cams of a camshaft: 49.20 mm intake valves, exhaust valves 49.15 mm. Limits wear 0.2 mm. The diameter of the necks of a camshaft 29,0935-29,955 mm.

The gap between the necks of a camshaft and holes supports: nominal 0,045-0,086 mm, the maximum allowable 0.1 mm. Maximum permissible palpation 0,05 mm.

The belt camshaft drive a Nissan pulled a semi-automatic tensioning roller.

Drive valve cams carried by the camshaft hydraulic tappets plungers mounted directly in the cylinder head.

Hydraulic tappet consists of two main movable parts: a pusher 3 (Fig. 3.13) serving simultaneously during operation of the plunger and the cylinder 4. Under the pressure of the spring 5 the piston and cylinder move away from each other, whereby selected clearance between the cam of a camshaft and end of the valve stem. Filling and closing of the chamber and the high pressure is provided by a check valve 1.

At the beginning of valve lift (Fig. 3.14, I), i.e. at the time of attack camshaft cam follower on the end of check valve closes the chamber and the pressure therein increases. Increased pressure does not reduce the volume occupied by the oil in the pressure chamber. Tappet thus operates as a solid. At the moment of the maximum valve lift (see. Fig. 3.14, II) a cam of a camshaft with a force pressing on the pusher, which leads to a significant increase in the pressure in the cavity of the pusher. A small amount of oil is ejected through leaks between the cylinder and the plunger, which leads to compression of the hydraulic tappet maximally 0.10 mm. This compression is necessary to structurally break-pushers with decreasing distance between the cam camshaft and the end of the pusher.

Payment clearance between the cam and the tappet (Fig. 3.14, III) is as follows. Camshaft cam is not pressing on the pusher, and the pressure in the pressure chamber decreases. Spring spreads piston and cylinder, selecting the gap between the cam and the end of the valve stem. At this time the check valve opens, some of the oil supplied from the storage chamber into the pressure chamber. This amount depends on the gap selected.

Increased noise of the drive mechanism of the valve after starting the engine is not a malfunction. Occurrence of noise due to the fact that when the engine of the oil flows from the cavity pushers. With the start of the engine high-pressure chamber is filled again and the noise stops. Filling the high-pressure chamber continues as long as the engine has warmed up to operating temperature. The design of the lubricating circuit of the cylinder head eliminates the complete removal of oil from the channel after the engine stops. It supplies the oil pushers immediately after engine start and an early end to the noise in the drive mechanism of the valve.

After stopping the motor of the channels extending from the oil pump, oil drains, and channels for supplying oil to the pushers remain filled with oil. In order to start the engine when the air is not done under the influence of the oil pressure in the cavity of the pusher in the oil lines to the follower, there are air vents that provide automatic purge cavity pushers. Also, vents can reduce the oil pressure supplied to the jacks (Fig. 3.14, IV and 3.14, V).

Table. 3.10 shows the timing of the engine CD20E.

Table 3.10 Valve timing engine CD20E

The frequency of replacement of the drive belt - every 90 000 km. Arrows marked on the belt, must correspond to the direction of rotation.