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.
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
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.
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!
Appearance of Used Head Gaskets
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.
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
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.
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
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.
Intake Manifold Gasket Installation
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%.
If manifold end gaps are too small due to head and
block surfacing, do not use end seals. Instead, use a bead of RTV silicone.
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
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
Inadequate seal lubrication before first-time start up is the leading
cause of rear main seal failure.
Seal Construction and Materials
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.
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
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
When installing No. 2909, be sure to review the instruction sheet included
for correct housing and shaft dimensions.