Lombardini CHD series - Hydraulic Tappet Operation; Hydraulic tappet operation; Injection pump follower

- 35 - Workshop Manual LDW CHD _ cod. 1.5302.345 - 6° ed_rev. 05
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Injection pump follower
Introduce the follower into its housing and manually turn screw 3
until it matches with notch 2.
Before locking screw 3useyourngertocheckthatthefollower
is allowed to move upwards freely.
Space 1 should be introduced into the pushrod with the at
surface facing upwards
Note: The screws 3a can be tted without distinction in each
cylinder.
Screw 3b however, which is shorter than the others, has
to be tted on the timing side of the cylinder (inside the
stop lever cover).
Hydraulic tappet operation
The operating principle of the hydraulic tappet is based on the
incompressibility of the liquids and on controlled leakage.
Through push rod 1, the pressurised oil gets into the tappet in
chamber A(low-pressurechamber),maintainingaconstantowof
oil in the above chamber as well as in the high-pressure chamber B.
The oil can only enter chamber B through the non-return valve 2
and leave through the clearance between the plunger 3 and the
tappet body 4 (controlled leakage).
Chamber B isrelledwhenthetappetisonthebottomofthecam
base and spring 5 keeps plunger 3 pressed, thus eliminating the
clearance in the entire valve-rocker arm-push rod-tappet-cam
system.
The tappet body moves away from the plunger creating a slight
vacuum in chamber B and causing the valve 2 to open, thus allowing
the oil in chamber A toowintochamberB, re-establishing the
quantity of oil required for optimal running conditions.
Disassembly / Reassembly
Difcultoperatingconditions:
For correct functioning of the hydraulic tappets the pressure chamber of plunger 3mustalwaysbelledwithoil.
However, this is not possible in some conditions in that, when the engine is not running, oil leakages may cause partial emptying
of the tappets. This situation will cause excessive clearance which will make itself apparent through an unusual ticking sound that
is not to be confused with the normal ticking of the injectors.
1 - Starting from cold: the engine has not been used for some time and oil may have leaked out of the pressure chamber of the
tappets.Moreover,lubricantowswithgreaterdifcultyatlowtemperatures,andhenceseveralsecondsmaygobybefore
the tappets are once again supplied with oil.
2 - Engine very hot: at minimum speed, the oil pressure is low and tiny air bubbles may form inside it (more than 5% of its
volume). This causes the lubricant to become compressible and the tappet is squeezed slightly creating clearance and,
thus making a noise.
3 - Starting and stopping the engine repeatedly (very rare): in this situation the tappets may empty temporarily.
Inallthreecasesthetickingshouldnotlasttoolong.Ifthisisnotthecase,theproblemisdenitelyduetoamanufacturingfault,
wear and tear or dirt, which can be drawn in by the oil and get between the non-return valve and its seat inside the plunger, thus
compromising the functioning of the tappets. In this case the hydraulic tappets must be replaced.