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Finding and Stopping Chevy Valve Cover Leaks

John Pfanstiehl Oct 4, 2017
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The Chevrolet small-block engine was a brilliant piece of engineering, attested by the fact that well over 100,000,000 were built. However the first generation was not as oil-tight as later generations. The gaskets between the valve covers and the heads are common culprits. They often weep, leak, and seep. A good part of the problem is that until 1986 small-block valve covers were attached by only four bolts located on their perimeter. Compounding that problem, flimsy stamped steel valve covers on base models and a narrow rough sealing surface on the cast-iron heads made leaks nearly inevitable.

On the bright side, valve cover leaks are about the least expensive oil leaks to fix. And valve cover removal is one of the easiest and most trouble-free ways to look inside your engine. Plus, if your engine compartment is looking a little dreary, replacing or refurbishing the valve covers provides a major improvement at relatively little cost. Due to the popularity of Chevrolet small-block and big-block engines, the choices in aftermarket valve covers are staggering.

We will pay particular attention to 1955-1986 small-block valve covers and gaskets. Big-blocks utilized seven bolts instead of the four on the first-generation small-blocks. Later generations of small-blocks (and first-gen engines starting in 1986) utilized center bolts instead of the perimeter bolts of the first generation. These and other design changes greatly improved sealing at the valve covers. Regardless of the design, the following information on valve cover considerations and gasket options is of value when replacement is needed.

Cover Considerations

From the first small-block engines in 1955 until head modifications in 1959, valve covers had a staggered-bolt pattern (the upper boltholes were a little over an inch closer together than the lower boltholes). That design may have been to ensure that the covers were not installed upside down. In any case, a prime consideration is whether the cover you need is a staggered or straight-across design. For those who have the earliest staggered-bolt heads but want to choose from the many more styles of the later straight-across bolt valve covers, an adapter is available.

An essential consideration for motors with high-performance aftermarket valvetrains is the internal height of the valve cover so that there's sufficient clearance to the rocker arms when the valves open. Note that a little extra height also can be gained by using thicker than stock gaskets.

Another essential consideration is the external height of the valve cover. In some engine compartments, there's very little clearance with the brake booster, air conditioning compressor, alternator, or other components. The intake manifold, EGR valve, or exhaust manifolds can create fitment issues, too.

A fourth important structural consideration concerns the openings in the valve covers. The early Chevy V-8s had none. These engines had oil fills and/or breathers on the intake manifold and some had a road draft tube on the rear to vent the engine. Later valve covers have openings for vents, PCV valves, and oil fills. The size, number, and location of these holes in the valve cover varied from year to year and even varied between engine options. Because of that, many aftermarket valve covers have no holes. If holes are needed in those covers, customers must either machine or drill them to suit their particular application.

The above considerations are structural and are critical. But they are fairly easy to inspect and measure to determine what you need. Cosmetic considerations are an entirely different story. There are so many choices for Chevrolet engines. For example, Summit Racing offers well over 100 styles for small-blocks alone. We'll leave those aesthetic considerations entirely up to you while we look at the numerous gasket options.

Gaskets Galore

It used to be simple. Valve cover gaskets were cork or cork with a rubber binder. These are still available and are good choices for many applications. They conform well to the narrow rough mating surface of early small-block, cast-iron heads. This is important with the relatively low clamping force of perimeter bolt covers, especially the stamp steel covers. The cork gaskets are generally the least expensive but they compress over time, requiring that the cover bolts be retightened occasionally.

After many years cork gaskets can compress too far and become hardened. It's common practice to cement these (and other types of gaskets) to the valve cover to hold them in place during installation and to keep the gasket attached to the valve cover during removal. On the lower gasket surface, Permatex Form-A-Gasket #2 or other non-hardening sealers can be applied to better seal against the head when the gasket compresses or the bolts loosen.

Cork valve cover gaskets are also available with a steel core laminated in between cork layers. A steel core prevents valve cover gaskets from being sucked in by high vacuum or pushed out due to excessive blow-by. Although this occurrence is uncommon on stock engines, the metal layer also helps cork gaskets retain their dimensions. Old cork gaskets can dry out and shrink. These multilayered gaskets retain the ability of cork gaskets to seal against rough surfaces and are a popular choice today.

Rubber valve cover gaskets have been an option for many years. For race applications, they have the added advantage of standing up to repeated removal and installation of the valve cover. The rubber material is relatively hard compared to cork and therefore sometimes does not conform as well to rough surfaces, especially with the few focused pressure points of perimeter bolt stamped steel valve covers. However, if valve covers are not likely to be removed, rubber gaskets can be coated on both sides with RTV or other sealants for a long-lasting, leak-free seal.

An example of the newer types of valve cover gaskets is Fel-Pro's molded silicone gasket with a laminated steel core. These gaskets additionally feature steel compression limiters, enabling the bolts to be tightened without overly compressing the silicone. These have garnered good reviews and represent the high end of valve cover gaskets at over $50 for a pair.

One more consideration in choosing valve cover gaskets brings us back to the early small-blocks with the staggered-bolt valve covers. This staggered designed is still an issue today because some valve cover gaskets have both staggered and straight boltholes (six holes total) to accommodate both designs. These six-hole gaskets have to be trimmed to fit some valve covers. And the extra holes create a thinner sealing area near two of the cover bolts.

Although valve cover gaskets don't necessarily need sealers or cements, it's common practice to glue the gasket to the valve cover. There are a number of sealant choices too. For this application, Permatex #1, RTVs, or Permatex High Tack gasket sealant work well. Tip: After gluing the gasket to the cover, place the gasket on a flat surface and place a weight on top of the cover until the sealant dries. Then remove any excess sealant to prevent it from being an eyesore on the outside or going into the engine from the inside.

Leak Checking

Before replacing the valve cover gaskets, check to make sure that they are the cause of oil drops on your floor. Feel for oil on the head around the lower rear corner of the cover. That's a primary problem area. The gaskets can also leak at the top of the valve cover causing oil to puddle at the edge of the intake manifold. Identifying the source of the leak in this area gets tricky because, although much less likely, the intake manifold gasket can also seep oil.

The seals at the front and rear of the intake manifold are another potential source of oil leaks. While inspecting the rear of the engine, also examine the oil pressure line or sender and the distributor gasket. Back to the top of the engine inspect any rubber grommets on the valve cover. They frequently harden and seep oil when they dry and shrink.

Moving below, inspect the underneath of the engine for oil leaks at the rear main seal, front main seal, fuel pump gaskets, and dipstick tube. In any case, you can follow along for tips on replacing the valve cover gaskets. On early small-blocks if they aren't leaking now, it's likely they will be at some time.


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