The valves are driven from the camshaft through tappets, pushrods and rocker arms (Fig. 1)
The camshaft is steel, forged, has five bearing journals, valve drive cams, an oil pump drive gear and a fuel pump drive eccentric.
The bearing journals of the shaft in the cylinder block on plain bearings are steel bushings filled with an anti-friction alloy (no bushings are installed on model 4178 engines from December 1995 and model 4218).
Fig. 1. Valve drive
The camshaft is driven from the crankshaft by a pair of gears with oblique teeth. The gear on the crankshaft is cast iron, and on the camshaft there is a plastic crown with a cast iron hub.
Both gears have two threaded holes for the puller.
Fig. 2. Alignment marks on timing gears: a - marks
The correct distribution phases are ensured by setting the gears according to the marks (Fig. 2).
The “O” mark on the crankshaft gear should be against the risk at the tooth cavity on the camshaft gear.
Fig. 3. Thrust flange of the camshaft: 1 - gear; 2 - thrust flange; 3 - spacer ring; 4 - camshaft
The axial movement of the camshaft is limited by a steel thrust flange 2 (Fig. 3) located between the end face of the camshaft journal and the gear hub.
A working gap of 0.1–0.2 mm between the gear hub and the thrust flange is ensured by the fact that the spacer ring 3, sandwiched between the gear and the camshaft journal, is thicker than the thrust flange.
