Working Principle; Precautionary Measures - Royal Enfield Classic 500 2009 Service Manual

Hydraulic Tappets

WORKING PRINCIPLE :

Engine oil enters the lifter through the
body feed hole, and flows into the inside of
the plunger through the plunger feed hole,
filling the "low pressure chamber" (E, in
Figure)
The oil flow continues around the check
ball and through the slots of the ball re-
tainer to fill the cavity below the plunger,
called the "high pressure chamber" (A, in
Figure). Oil is forced down into this area
by momentary low pressure which occurs
once during each valve event (cam revolu-
tion), which the RHVL roller bearing in
on the cam base circle.
As the RHVL rises up the nose of the cam
and the full load of the valve train is ap-
plied on the lifter, a predetermined and
closely held clearance of .0002/.0003 inch
(.0051/.0076 mm)between the outer diam-
eter of the plunger and the inner diam-
eter of the body permits a controlled
amount of oil to escape up from the high
pressure chamber.
This controlled oil leakage compresses the
plunger spring and allows a small relative
movement of the plunger with respect to
the body. This movement is called
LEAKDOWN (see Figure 04-4) and occurs
once during each valve lift event.
As the RHVL rides back down the flank of
the cam and returns to the base circle, the
plunger spring provides the force to main-
tain zero back lash and forces the plunger
back to its original position relative to the
body. This allows engine oil to once again
fill the high pressure chamber so the cycle
can be repeated.
The volume of oil that enters the high
pressure chamber during each base circle
event is equal to the volume of oil that is
lost through the plunger-to-body diametral
clearance during the valve lift event
(Leakdown).
(Roller Hydaulic Valve Lifter (RHVL)
The overhead oil supply is accurately me-
tered from the "low pressure chamber",
which is at engine oil pressure, by using
a flat metal disk (metering valve C, in Fig-
ure), which wobbles against a cylindrical
radius curved surface on the bottom of the
push rod seat (D, in Figure). Oil then flows
up through the hole in the push rod seat
to lubricate the overhead valve train com-
ponents (oil flow path B, in Figure).
The metering valve moves sufficiently to
keep the push rod seat hole free and un-
clogged. When the engine is shut down,
the valve seats on the shoulder of the
plunger to minimize drain back of oil.
If the engine structure or valve train ex-
pands or contracts with changes in en-
gine temperature or other differentials,
the RHVL will automatically adjust its own
internal length to compensate for these
changes.

PRECAUTIONARY MEASURES :

holes for the oil to circulate and to also
act at the hydraulic media. Hence oil con-
tamination must be as less as possible. For
this, all the filters ( oil filter on cover RH,
sump drain filter with magnet and sec-
ond drain plug with magnet ) must be
cleaned periodically as mentioned in this
Service manual.
service / replacement or stored in spare
parts, they must be kept upright (the
rollar side surface pointing downwards and
the push rod seating surface at top side
as shown in fig. below) to prevent the oil
from drian off.
✓
04-6
The hydraulic tappets have minute
Whenever the RHVL is removed for
✕
✕