=
Search

Timing system and tappets

 

The timing system is equipped with hydraulic tappets that automatically recover the operation of the rocker rods assembly.
No registration is therefore required.

 

2.16.1 Components identification

Fig 2.52

 

Tab 2.35

POS. DESCRIPTION
1 Crankshaft
2 Camshaft
3 Camshaft tappets
4 Rocker arm control rod
5 Rocker arms
6 Valves
7 Injection pump control gear
8 Camshaft control gear
9 Intermediate gear
10 Intermediate gear pin
11 Crankshaft gear
12 Valve control bridge
13 Articulation control valves
14 Hydraulic tappets

Fig 2.53


Fig 2.54
2.16.2 Rocker arm pin

Tab 2.37
POS. DESCRIPTION
1 Rocker arm pin
2 Rocker arm distancing spring
3 Rocker arm pin support
4 Exhaust rocker arm
5 Intake rocker arm

Fig 2.56
2.16.3 Rocker arms

Tab 2.38
POS. DESCRIPTION
1 Rocker arm body
2 Hydraulic tappet oil refill line
3 Valve tappet lubrication line
4 Valve tappet
5 Hydraulic tappet
6 Oil flow line

Fig 2.57
2.16.4 Hydraulic tappets

Tab 2.39
POS. DESCRIPTION
A Hydraulic tappets
B Hight pressure chamber
1 Hydraulic tappets oil refill pipe
2 Retaining ring
3 Piston
4 Unidirectional valve
5 Tappet body


2.16.4.1 Hydraulic tappet operation

The operating principle of the hydraulic tappet is based on the incompressibility of the liquids and on controlled leakage.
The oil under pressure enters the tappet chamber A, providing a constant supply of oil in the low-pressure chamber.
Through the non-return valve, 4 the oil can only access the high-pressure chamber B and exit via the clearance between the piston 3 and the tappet body 5 (controlled leakage).
The chamber B is filled when the rocker arm is on the base radius of the cam and the spring 6 keeps the piston 3 against the valve stem, thus eliminating any system play. Thanks to the spring extension, the tappet "extends", creating a small depression in the chamber B, making the non-return
valve 4 open, and allowing the oil in the chamber A to pass to chamber B, restoring the proper amount of oil required to eliminate any play in the valves.
Fig 2.58

2.16.4.2 Difficult operating conditions


For proper operation on the hydraulic tappets it is essentia that the low pressure chamber of the piston 3 is always full of oil.
In some conditions this may not occur (due to the fact that the oil leaks away when the engine is switched off, which can also partially drain the tappets). This situation will be the cause of clearances that will result in a characteristic noise similar toa ticking sound.

 

  1. When the engine is cold, the tappet filling time could be very long if the oil used is not suitable for the specific environmental conditions (Tab. 2.2)
  2. If the engine is very hot: at idle speed, oil pressure may be low, and small air bubbles could form in the circuit. Because of this, this compressing the tappet slightly and producing valve play which is responsible for the ticking sound. On account of this, the tappet compresses slightly giving rise to a valve clearance, thus generating a slight ticking sound, which however disappears rapidly (MAX 10 seconds) once normal operating conditions have been restored.

Anyway the duration of ticking Anyway the duration of ticking sound must be MAX 30 seconds. If not, the problem is surely due to the poor quality of the oil, wear or impurities that, transported by the oil, can infiltrate between the ball valve and its seat inside the piston, compromising the operation of the tappet itself; In these cases, the only solution is to replace the oil or hydraulic tappets.

The prolonged persistence of the ticking sound or abnormal noise must be investigating in order to prevent any malfunctions; if necessary, replace the hydraulic tappets and engine oil.

 

Wait Loading