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The Right Way to Replace Valve Covers Gaskets

How To Cure A Common “Head” Ache

John Pfanstiehl Jul 11, 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 have been 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, only four bolts located around the perimeter attached small-block valve covers. Compounding that problem are 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-’86 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 that 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 engines 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 are 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 between it and the brake booster, air conditioning compressor, alternator or other components. The intake manifold, EGR valve or exhaust manifolds can also cause fitment issues.

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 stamped-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 a 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 No. 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 when 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 a common practice to glue the gasket to the valve cover. There are a number of sealant choices, too. For this application, Permatex No. 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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1. Inspect the bottom of the valve cover at the rear. If it’s shiny with oil then you can be pretty certain your valve cover gaskets need replacing. However, if it feels like your valve cover bolts are bottoming out, you might just need to add a flat washer or two to stop the leaking.

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2. If oil is puddling near the intake manifold, that’s also a common sign of valve cover gasket failure. Oil can also seep past the intake manifold gasket near its center but that is much less common.

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3. Traditional cork gaskets are still a popular choice and can seal well against the rough narrow sealing surface of cast-iron heads. However, cork tends to compress over time, requiring valve cover bolts to be retightened. Eventually the cork gasket compresses too far in its center allowing oil to get by.

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4. Remove the valve covers and remove any sealant or gasket from the heads. Avoid the drain hole to keep these bits from falling into the engine. Soak up the oil by the lower rear and front head bolts to spot any debris that is hiding under the oil.

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5. Clean out the boltholes in the head by turning a 3/16-inch drill bit by hand. Over the years gasket material or sealant can build up in the bottom of the hole, preventing the bolts from tightening on the valve cover.

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6. Screw a bolt all the way into each hole and then unscrew it counting how many full turns before it comes out. Also note if the threads bind during the last few turns; that will make it difficult to tell how much pressure is being placed on the gasket. If the bolt bottoms out when installing the valve cover it doesn’t matter how good the gasket is—it will leak. After the boltholes were cleaned, these 1973 heads allowed just over nine turns.

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7. Block off the baffles when scraping the old gasket and cleaning the valve cover. The baffles help prevent oil droplets from being sucked into the PCV valve, vent tube and hoses. Also note the projections on the inside of this factory valve cover. These drippers aid in oiling the rocker arm pivot.

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8. It is essential to place some type of straightedge against the gasket surfaces of stamped-steel valve covers to see if they are bent. They usually are deformed near the bolt holes and they won’t seal until that’s fixed. Support the upper surface of the flange on a block and tap on the lower surface near the bolthole until it is straight again.

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9. There are many choices in valve cover gaskets. There are even choices in cork gaskets. In addition to cork gaskets being available in a number of different thicknesses, cork gaskets can also have a steel layer laminated in the center as seen here.

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10. Mr. Gasket offers a 0.325-inch thick cork gasket. This extra thickness can provide increased clearance for aftermarket valvetrain components or it can help prevent the valve cover from hitting the intake manifold.

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11. This silicone Fel-Pro gasket from Summit Racing is a good example of high-end sealing. In addition to its laminated metal core, it has metal sleeves around the boltholes to prevent the gasket from being crushed too far. This also allows the bolts to be tightened to the point that they are less likely to loosen up.

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12. Paragon’s gasket has cork bonded with rubber for better dimensional stability. The extra bolthole enables it to be used on the early small-blocks that had valve covers with staggered bolts. The thickness is similar to OEM gaskets at about 9/64-inch.

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13. Paragon also offers original style valve cover bolts, screws and retainers. The factory retainers are often missing but they are essential to distribute the force of the bolts on the thin stamped-steel valve covers. Note that the factory bolts used with aluminum valve covers have 3/8-inch hex heads.

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14. The choices in aftermarket valve covers are extensive. Holley’s new Vintage Series finned aluminum valve covers with Chevrolet script come in natural cast finish, polished, satin black or factory orange with machined fins. Holley-scripted models are also available with or without PCV and oil fill holes (and these come with pre-installed internal oil baffles).

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15. Three critical structural considerations in selecting a valve cover are the internal height for clearance with aftermarket valvetrain, external height for clearance with nearby components and any holes needed for a breather tube, PCV valve or oil fill. The latter two considerably narrow the choice on some cars.

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16. This is a good time to inspect all the rubber grommets on the valve covers. They harden over time to the extent that pieces can break off and fall inside during removal. Be aware that the grommets made for steel valve covers have a narrower channel than the ones for aluminum valve covers. Paragon offers these original style grommets plus new emblems and stickers to restore factory covers.

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17. It’s important to check to see how far the bolt goes through the valve cover and gasket. At least three threads should be showing, especially when used with aluminum heads. However, more than five threads extending out can be a problem with some stock heads because the boltholes are relatively shallow. Our 1-inch long bolts worked well with the Holley Vintage Series covers and a thick gasket.

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18. Permatex High Tack is popular for gluing the gasket to the valve cover. This holds the gasket in place during installation and keeps it attached to the cover during later removal for valve adjustment or other work. Permatex Ultra Copper Silicone RTV also works well in this application. Both are available from Summit Racing.

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19. A thin coat of Permatex No. 2 on the lower surface of the valve cover gasket helps make it oil tight, especially on the narrow sealing surface of early small-block cast-iron heads. It also helps keep the oil in when gaskets compress or cover bolts loosen. Permatex No. 2 is non-hardening so the covers can be removed later without breaking the gaskets.

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20. Make sure that the valve cover has clearance with the intake manifold. The upper lips of factory aluminum valve covers were trimmed in this area. Similar trimming can often be done on aftermarket valve covers when needed.

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21. Holley also makes finned die-cast aluminum air cleaners in their Vintage Series. These come in 3-inch and 4-inch heights with a choice of premium dark red or natural paper air filter elements. A center stud, wing nuts, and gaskets are included.

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22. The exterior surface of unpainted aluminum valve covers can tarnish over time. Tip: spray a little Corrosion Block on a cloth and wipe aluminum parts to protect them. It can even help restore a little sheen to an old valve cover, as seen on the right side.

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23. The combination of the Holley Vintage Series valve covers and matching air cleaner add a substantial amount of bling to an engine compartment. Replacing valve covers or gaskets is one of the easiest at-home projects. And with no drips, your garage floor will look better, too.

Photography By John Pfanstiehl

Sources

Summit Racing
Akron, OH
800-230-3030
http://www.summitracing.com
Holley Performance Products
Bowling Green, KY 42101
270-782-2900
http://www.holley.com
Paragon Corvette Reproductions
Swartz Creek, MI
800-882-4688
https://www.paragoncorvette.com/

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