These pages are devoted to
the 1991 3000GT VR4
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Valve
Lash Adjuster Check and Repair
Most
rocker arms are bolted in the center and pivot at this center anchor point
with a push
rod on one end that goes down
to lifters that ride on the cam and the valve stem on the other side
similar to an upside down teeter
tauter These engines do not have lifters as one would normally
think of lifters however they
function in a similar manner in that they cushion the shock of lifter
movement with oil and expand
to maintain tolerances. They do not lift the rocker arm with a push
rod as in conventional engines
but are a "dampener" on one side of the rocker arm The cam in this
case rides on the center of
the rocker arm and on one side is the valve stem and on the other
side are the lash adjusters.
The lash adjusters act like a mounting point or bolt (but do not bolt in)
on
one side to retain the rocker
in place and are always fully extended with oil pressure. In the event
the
valve does not move down at
the same speed as the cam is trying to push it, the lash adjuster being
filled with oil has the ability
to force oil back out of it and take up the slack Here is a close up photo
of
the lash adjuster and cam setup
so you can relate the previous text to the photo.
The following is a exact copy
of the text from the manual on the repair and checking of the lash adjusters
with photos from the manual
Page 11-16
LASH ADJUSTERS CHECK
If an abnormal noise is heard
from the lash adjusters check as follows
(1) After warming up the engine, stop it.
(2) While installed to the cylinder head, press the part where the rocker
arm
contacts the lash adjuster at the very top. If the adjuster is normal,
the
part pressed will be very hard.
(3) If it easily moves all the way downward when pressed, there is a malfunction
of the lash adjuster and should be replaced with a new one
(4) If it feels spongy or elastic, probably oil with air mixed in it has
entered the
lash adjuster. Check whether the amount of oil is too much or is not enough
and the cause of air becoming mixed into the oil is a damaged oil screen
or
oil screen gasket
(5) After repairing the cause of the air leak, warm the engine and then
drive the
vehicle at slow speed for a while. Stop the
engine and leave it off for a few
minutes: then restart the engine and drive at low speed. Repeat this procedure
several times during the course of about one hour so as to remove the air
from
the oil.
Page 11-22
Moving over to page 11-22 we
see that the oil screen is located in the oil pan. The active aero front
dam must be removed to get at
the cross member under the oil pan. The oil pan must be removed
and the oil screen checked.
It is advisable to obtain a new gasket at the same time or have gasket
stock ready to make a new one
as long as you have the oil pan off I would also suggest a new pan
gasket and oil return gasket
at the same time. The pan gasket is sealant #MD997110 or
equivalent. Permatex Ultra Blue
would suffice in this application. There are two oil return gaskets,
one on each side of the oil
pan as seen in the photo below but this only applies to the twin turbo
model
Once you have eliminated the
leak, we can go through the process above. Mind you, the same problem
will occur if the oil level
is low in the pan or sometime during hard long cornering the oil pump could
pick
up air, so don't jump the gun
here and think you have problems as soon as you hear lash adjuster noise.
It is common and "OK" if it
goes away, so don't go ripping apart an engine unless you suspect problems
and they don't go away in a
short while
Page 11-32
If you have determined that you
have a faulty lash adjuster from the directions above, replace it using
the following procedure from
page 11-32 in the manual
|
SERVICE POINTS OF INSTALLATION
11.
INSTALLATION OF LASH ADJUSTER
(1) Immerse the lash adjuster
in Clean Diesel Fuel
(2) Using a small wire, move
the plunger up and
down 4 or 5 times while pushing down lightly
in the check ball in order to bleed out the air
(3) Install the lash adjuster
to the cylinder head |
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Last update 1/08/99