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Cylinder Head Gasket Replacement | Buyer's Guide

6/9/2021
Tags: Tech, Tech, Engine
Head Gasket Considerations
An assortment of different head gaskets.

When it comes to installing a new pair of head gaskets, it’s not unusual to have a few questions about your options. For example: should you use a copper or a graphite gasket? What does it mean if the gaskets have pre-flattened fire rings? Should you coat the gaskets with sealer before installing them? These are all great questions and it’s our goal to clear up any confusion on the topic.

We know combustion temperatures and pressures are pretty darn high (around 2,000°F and up to 1,000psi) and even higher on boosted applications. But, it’s the job of the head gasket to seal up the vulnerable gap between the block and head, all the while directing and sealing the hot coolant and oil. These factors are exactly why it's so important to have a basic understanding of head gasket designs.

Head Gasket Designs

There are two main types of head gasket constructions: composite and metal. A composite gasket will have thin gasket sheeting bonded to a steel core with a fire ring at the cylinder bore. A metal type gasket can either consist of a shim steel design, multi layer steel, or solid copper. Shim steel gaskets are one of the oldest types of gasket designs, which are purely stamped steel that come in a variety of thickness combinations. Multi-layered steel (MLS) is a relatively newer design that consists of two or more embossed stainless sheets molded to a flat metal core. The last type of metal gaskets is a solid copper design. Copper is one of the strongest and most conforming types of metal and copper style gaskets offer many options for bore and thickness combinations.

When gaskets are advertised having pre-flattened wire rings or “fire rings,” this means the ring sealing the combustion chamber has been pre-flattened to prevent any surface damage to aluminum heads. Fel-Pro Gaskets offers several different types of MLS pre-flattened steel or copper ring style gaskets.

Which Gasket Should I Use?

If you’re installing aluminum cylinder heads, we always recommend using gaskets with a soft copper wire ring, such as the Fel-Pro Copper Ring Head Gasket for small block Chevy engines. This will ensure that the aluminum head is not "scarred" by the combustion seal when you torque the heads. Another option for use with aluminum heads would be a shim style like the Fel-Pro Embossed Ring Head Gasket . On Flathead Ford V8 engines, anytime you’re using aluminum cylinder heads we recommend using a copper head gasket like this Flathead Big Bore Gasket for 1939 to 1948 engines, or the Best Gasket Flathead Big Bore, for 1949 to 1953 engines.

Head Gasket Coatings

There are mixed feelings on whether or not you should apply a sealer or coating to head gaskets before installing them. Some guys like to apply a "copper coat", such as KW Copper Coat or Permatex Copper Spray-A-Gasket. Years ago, some would even spray paint their gaskets before installing them. The idea is that it should help seal up small imperfections in the deck or head surfaces. Success can be achieved with and without copper spray - the individual manufacturer will usually specify whether or not you should use sealer with their gaskets.

Head Gasket Installation Tips

For head gaskets to seal properly, the head and engine block deck surfaces must be clean, smooth, and flat. The presence of any foreign material (dirt, carbon, old gasket material, abrasive residue, etc.) on either surface can cause an improper seal. Debris can act like a bridge and form pockets that create a path for leakage to occur. Any debris can also become embedded in the surface of the gasket. Debris may even damage the surface of the head and/or engine deck surface, which can lead to repeated gasket failure. The diagram below can be used as a generic reference for small block Chevy engines. Simply reverse the sequence when disassembling.

Diagram explaining the order in which head gaskets should be torqued.
Inspecting Head Gaskets for Damage

Inspect the old gasket for wear and damage. This will provide clues to previous as well as potential future problems. A cracked gasket may indicate abnormal combustion like detonation or pre-ignition. Replacing the gasket without correcting the problem can cause even the highest quality gasket to fail. One of the most commonly overlooked steps while installing new head gaskets is forgetting to apply sealer to the head bolts when needed. If the head bolts thread into a cooling passage you must apply sealer to the threads or coolant will leak through the bolt passages.

Always check for warpage or distortion by placing a straightedge lengthwise and widthwise on the head and deck surfaces. You can check for any distortion with a feeler gauge between the deck or head surface and the straightedge. Widthwise, all applications should not be more than .002-inches out-of-flat.

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