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Felt-Pro Tips
Head
Gaskets
Water Circulation
Intake Manifold Gaskets
Rear Main Bearing Seals
HEAD
GASKETS
Surface Finish
Head and block surfaces can cause sealing problems if they are too
smooth or too rough. Too smooth a surface allows excessive lateral
motion of the head gasket, which can deform the combustion seal.
Too rough a surface creates small leakage paths. Prepare the head
and block surface in the 90-110 RMS (80-100 RA) range. That is
just enough to feel with your fingernail.
Surface Flatness
To maintain constant contact between the gasket and the head and
block, deck surfaces must start out flat and remain flat after the
fasteners are torqued. The maximum initial "out of flat"
as measured with a straight edge and feeler gauge should not
exceed .0025" in any direction. To find out if the surfaces
are staying flat during engine operation, it's necessary to
"map" the used gaskets. Wipe them off and trace the
outline on a piece of paper. Measure the thickness of the gasket
body within 1/4" of every bolt hole and at a point midway
between bolt holes. In addition, try to find an area of the gasket
body that has not been compressed and measure the thickness there
as well. The compressed areas should be .003-.004" thinner
than the uncompressed areas, and all compressed thicknesses should
be within .001-.002" of each other. If the compression is
inadequate or uneven, the clamping force can be changed by raising
or lowering the torque on the fasteners in those areas 5 lb-ft at
a time. This will fine-tune the load on the gasket and result in
less flange bending. Examine the gaskets again at the next
tear-down. If they are evenly compressed, the head and block are
staying flat while the engine is running. This reduces cylinder
bore and valve seat distortion which makes more power.
Clamp Load/Torque Procedures
Insufficient clamp load is the cause of many head gasket problems.
If the gasket is not tightly clamped between the head and the
block, combustion gases and engine fluids can leak past the
gasket.
The key to sufficient clamp load is
to have adequately stretched head bolts or head studs. Proper
clamp load will not be reached if head bolt assemblies (or
stud/nut assemblies) have too much friction. This is because
torque wrench readings will reach specification before adequate
bolt stretch has been achieved. Clamp load normally declines
moderately over time as the head gasket "relaxes" and
bolt stretch is reduced. We measure this as "torque
loss" of the bolts. Clamp load can decline excessively due to
extreme engine temperature, excessive head motion or detonation.
For proper installation:
·Use
hardened washers under bolt heads (or nuts) to prevent galling of
the cylinder head and to reduce friction.
·Tighten head bolts (or nuts) with a smooth motion. Sudden or
jerky movement of the torque wrench gives false readings,
resulting in clamp loads as much as 20% below normal.
·Follow the recommended torque pattern and tighten bolts or nuts
in at least three steps, up to the specified torque.
·Fastener torque specifications shown on page 37 are for use with
moly, or anti-seize. Motor oil or EP grease is not recommended.
Bolts which enter the engine's water jackets should be sealed with
Teflon sealer. If more clamping force is required to correct a
sealing problem, the torque can be raised 5 to 10 lb-ft at a time
until the problem is corrected. Just remember that excessive
torque can strip the threads, break the fastener or permanently
warp the flanges. Approach the problem carefully and slowly. Don't
try to use excessive torque to make up for warpage or defective
surfaces -- it won't work!
With higher
installation torque, it's more important to chamfer the bolt holes
in the head and the block. This will prevent the threads from
pulling up and distorting the block deck surface which can keep
the gasket from being compressed properly. If you have doubts
about how much chamfer is needed, examine the gasket around the
bolt holes. If there are signs of gasket crushing within
.050-.100" of the bolt hole, increase the amount of chamfer
slightly.
·In severe
service, such as racing, retorquing is recommended to restore
maximum clamp load. After a complete engine warm up and cool down,
retorque the bolts or stud/nuts to specification.
·In circumstances where
retorquing after running the engine is
not possible, the next best method is retorquing before the engine
is taken off the engine stand. After torquing the fasteners, wait
at least 10 minutes, back off each fastener, one at a time,
1/8-1/4 turn, and pull them back up to the torque specification.
This will allow for gasket relaxation and thread engagement
variations, and will ensure consistent clamp load.
Appearance
of Used Head Gaskets
Learning to "read" a used head gasket can help you solve
some problems and prevent others before they happen. A "plug
light" with a magnifier is an ideal tool for close
examination of the gasket.
·Examine
the combustion armor for carbon tracks which indicate either
combustion leakage or that the armor was hanging into the
combustion chamber or cylinder chamfer.
·Examine armors for discoloration of the stainless steel. This is
a sign of excessive casting temperatures.
·Look for signs of seepage around coolant holes. A gasket that
was sealing properly will have distinct impressions of the
castings around coolant holes. If impressions are not distinct or
if the gasket coating has been washed away, there was probably a
coolant leak due to inadequate clamp load or excessive head
bending.
·Measure the used gasket with a micrometer to see if it had been
properly compressed as described in surface flatness section.
WATER
CIRCULATION
Most head gaskets combustion seal failures occur because of
excessive heat in the gasket sealing areas. To correct the
situation, more coolant flow must be provided to these areas. This
can be accomplished through the use of amore efficient water pump,
higher pump speed, restricting the coolant flow out of the engine
(increases jacket pressure) or revising the coolant holes in the
castings and/or the gaskets. Remember to make only one change at a
time so the effect of a particular change can be determined.
·Many OE
and aftermarket water pumps do not flow sufficient coolant evenly
to both sides of the engine. We highly recommend newer design high
performance pumps.
·To maximize the life or head gaskets, the use of electric water
pumps is not recommended. They often do not flow sufficient
coolant to prevent hot spots in the engine, even if the
"gauge" temperature is normal.
INTAKE MANIFOLD GASKETS
Due to the surfacing frequently done to performance heads and
blocks, it is easy to have the intake manifold "fit"
change significantly. Common problems are non-parallel head and
manifold surfaces, and reduced manifold end gaps.
·Check to
see that the head/manifold gasket surfaces are parallel. If there
is a noticeable difference in the gap at the bottom of the ports
versus the top surface of the ports, the castings will require
re-machining. Measuring the thickness of used gaskets also can
help detect a non-parallel surface.
·Be sure to tighten intake manifold bolts in a criss-cross
pattern to ensure even compression of the gaskets.
·Check end seal gap between the manifold and block. End strips
should be compressed 15%-60%.
·f manifold end gaps are too small due to head and block
surfacing, do not use end seals. Instead, use a bead of RTV
silicone.
Intake Manifold Gasket
Installation
Most Fel-Pro performance intake gaskets are designed without a
metal core, to allow port trimming. Gaskets must be firmly adhered
to the cylinder head to avoid possible gasket movement.
Attach intake manifold gaskets to cylinder heads with a
firm-setting contact adhesive. Be sure to use it around intake and
water ports. Allow it to dry thoroughly before trimming the gasket
and permanently installing the manifold. However, you may
temporarily install the manifold to help locate the gaskets while
the adhesive is drying. This procedure is especially important on
large port heads with narrow walls between ports.
Exhaust Crossover
Most street engines use exhaust crossover to improve cold weather
driveability. Race manifolds do not have exhaust crossover because
they are designed to keep the carburetor cool.
Select the proper Fel-Pro
Performance Gasket depending whether the engine has exhaust
crossover which is to remain open, has exhaust crossover you with
to block, or does not have exhaust crossover. Fel-Pro Performance
intake gaskets are designed for manifolds without exhaust
crossover, except where noted in the catalog.
REAR MAIN
BEARING SEALS
Seal Installation
Inadequate seal lubrication before first-time start up is the
leading cause of rear main seal failure.
·Lubricate
the seal lip and crankshaft with oil or grease. Use grease if
there will be a long period of time before start up.
·Debur the edge of the block and cap to prevent damage to the
back side of the seal during installation.
·If there is a slight mismatch of the bearing cap and block, it
will help align the seal halves if you offset their parting line
about 3/8" from the cap/block parting line.
·To ensure that there are no leaks in the parting line are, place
a thin coating of RTV on the end of each seal half.
·There is a radius in the cap register of the block and a
matching chamfer along the sides of the cap. This creates a leak
path which must be sealed. When installing any rear main seal,
remove any oil film from the block register and apply a SLIGHT
amount or RTV silicone or anaerobic just prior to installing the
cap.
Seal
Construction and Materials
There are three basic types of rear main bearing seals: rope type,
1-piece molded and 2-piece molded. In general, the same type is
used in service as was installed as original equipment. One
exception is No. 2903, which is a 2-piece molded seal for Buick V6
to replace the original rope-type seal.
Fel-Pro performance seals are made of high-grade materials such as
silicone or polyacrylate. Ford or Chevy race engine builders have
an option of using special high temperature fluroelastomer seals.
Chevrolet 400 Small Block Race
Engines
These engines are a special case because when they are align bored
and honed, the original seal housing bore is enlarged. In the
past, the engine builder had to shim up a conventional seal to
fill the enlarged opening. Fel-Pro offers No. 2909 with enlarged
outside diameter to eliminate shimming.
When installing No. 2909, be sure
to review the instruction sheet included for correct housing and
shaft dimensions.
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