3363696 - INTRODUCTION - TIMING SYSTEM

CONSTRUCTION SPECIFICATIONS

CAMSHAFTS

Two ductile cast iron overhead camshafts operated by a toothed belt. - There are suitably directed cams on the camshafts with a suitable profile, in the same number as the valves to be operated; at the front they are prepared for fitting the toothed pullies by means of which they receive the movement from the crankshaft by mens of a suitably tensioned toothed belt (see chapter on "procedures for repairs").

Hydraulic tappets

The hydraulic tappets automatically take up valve clearance during engine service. This offers the advantage of reducing:

• maintenance operations
• engine noise.

Operation in open stage

When the camshaft cam acts on the cup (1) and thus the piston (2), the oil trapped in the chamber (6) due to the closure of the ball valve (4) trasmits the movement of the piston (2) directly to the hose (3) and consequently to the valve. At this stage, due to the high pressure acting on the oil, some of the oil in the chamber (6) leaks through the tiny gap between the piston (2) and the hose (3).

Operation in closed stage

During valve closure, as long as the tappet pressed by the action of spring (5) follows the cam outline, a vacuum builds up inside chamber (6) that brings about opening of ball valve (6) to allow oil to enter. The oil taken into chamber (6) replaces the oil that leaked out during valve opening.