Valve timing mechanism — design description (VAZ-2108)

The valve timing mechanism consists of a camshaft 5 (figure 5), valves 2 and guide bushings, springs with fastening parts and valve tappets 3. The mechanism parts are located on the cylinder head 1.



The valves are actuated directly by the camshaft cams through cylindrical tappets 3 without intermediate levers. In the tappet seat there is a washer 6, the selection of which regulates the gap A in the valve timing mechanism.

Cylinder head

Cast from aluminum alloy, has a wedge-shaped combustion chamber and pressed-in cast-iron seats and valve guides. The upper part of the bushings is sealed with metal-rubber oil-deflecting caps 7. The holes in the guide bushings have spiral grooves to improve lubrication. The inlet valve bushings have grooves cut to half the length of the hole, and the exhaust valve bushings have grooves cut along the entire length of the hole.

The original can be found on the website [VazBook.ru]

In the upper part of the cylinder head there are five bearings for the journals of the camshaft. The bearings are made detachable. The upper half is in the bearing housings 4 (front and back), and the lower one in the cylinder head. The holes in the supports are machined together with the bearing housings, so they are not interchangeable and the cylinder head can only be replaced together with the bearing housings.

Camshaft

Cast iron, cast, 5-bearing. On the rear side of the shaft there is an eccentric for driving the fuel pump. The working surfaces of the cams, eccentric and the surface under the seal are bleached to increase wear resistance.

Camshaft drive

It is carried out by an elastic toothed belt 6 (figure 6) from toothed pulley 1 of the crankshaft. The same belt also drives pulley 2 of the coolant pump. Roller 3 serves to tension the belt. It rotates on an eccentric axis 7 attached to the cylinder head. By turning the axis relative to the fastening stud, the belt tension can be changed.



To check the correct relative position of the drive pulleys, there are alignment marks: B on pulley 5 of the camshaft and the corresponding protrusion A on the rear cover 4 of the belt; G on pulley 1 of the crankshaft and the corresponding mark B on the oil pump cover.