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:

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. 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.

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.

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
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.

Seal Installation
Inadequate seal lubrication before first-time start up is the leading cause of rear main seal failure.

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.