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!

• 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.

• 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%.
• 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.

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.

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.