944 hydraulic lifter
information
The lifters used in the 944 are
technically referred to as “hydraulic tappet lifters”. The purpose of the
lifters
Is to ride on top of the valve stems, and
transfer the lift pressure applied from the lobes on the cam shaft.
Each lifter has a small oil bore, that allows pressurized oil from the engine’s
lubrication system to “pump up” the internal plunger.
Quite often, if a car has sat for a long
period of time, the oil can drain out of the lifters causing
Lifter noise when the car is eventually
started. This is normal and usually quiets down after a few minutes of running.
If you do experience excessive lifter
noise when starting the car, SeaFoam or Marvel
Mystery Oil can be added to
The oil to lower the viscosity and provide
additional detergents to assist in reviving the soft lifters. If you add either of these
Additives to your vehicles oil, be sure that the oil is changed within 30 miles to
prevent engine bearing damage!!
However, sometimes with the lifters
sitting dry In the cam tower, they no longer have the
ability to pump back up.
In this situation, the dead lifters must
be replaced.
Here is a photo of a 944/951 hydraulic
lifter:
Note the small oil bore on the side of
the lifter.
A good lifter, when not filled with oil,
should begin to depress the piston under 4.5 pounds of force, and become fully
Depressed under 7 pounds of force. The piston should depress 3/32 to 1/8 of
an inch before stopping:
Lifters that are removed from the cam
tower, or are being kept as spares should be stored in a container
Of oil with the oil bore facing up. This allows any air in the lifter to escape
and the resulting
Volume to be occupied by oil. We usually store lifters in a mixture of
conventional 10W30 motor oil with %10 SeaFoam
additive.
If you need to replace lifters in your
944, there are aftermarket lifters available. However…
Many people have had negative experiences
with the aftermarket lifters, thus it is recommended that you
Seek out original lifters that have been
removed, tested and stored properly.
If you will be reusing any lifters from
your car, be sure they are stored in a fashion that allows you to
Replace them in the same bores they were
removed from!
Before installing lifters into the cam
tower, they should be “primed” by hand to assure they are full of oil.
This is accomplished by holding the
lifter under oil with the oil bore facing up, and depressing the piston several
times.
If the lifter is functioning properly,
you will begin to feel the lifter piston become stiff as the
Internal chamber fills with oil. If after several depressions of the piston,
you do not feel it become firm, then the lifter should
Be replaced. The theory of the lifters is
based on fluid dynamics. A liquid can not be compressed,
Therefore, as the lifter become filled
with oil instead of air, it becomes difficult to “squeeze” the viscous oil
Out of the small oil bore.
Should you have questions on this
procedure, or need more information, feel free to email us: