Silicone Valve Cover Gaskets

Engine, Transmission & Driveline

  1. BillGrissom

    BillGrissom Active Member

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    I posted a few months ago asking about gaskets, and there were several useful replies, but can't find it.

    In searching for the recommended silicone gaskets, I found what looks like high-quality ones at less price - Real Gasket of Elizabethton, TN. They specialize in aircraft engine gaskets, but make some for collector vehicles. I bought both BB ($30.50) and SB ($25.20) sets. Chris signed the receipt as a Mopar Man with a 67 Cuda 440.

    Unlike the photo, I ended up putting the gasket on the head, sliding the cover down, then attaching the tabs. I torqued to the spec'd 2 ft-lb, which is not much. The hard part was over an hour removing the bare silicone I used on the last pass. But the biggie was the broken stud fiasco.

    It broke a few months ago when I tried tightening the nuts and forgot I had used jam nuts. I was able to drill it thru well-centered and was about to tap it out, which is the only success I have had removing broken bolts. Then I thought why not try a screw extractor since that will avoid thread damage. It broke off under not much torque (again!). Almost impossible to drill out the hardened steel, but I tried for hours. I understand some shops can burn one out. I almost drilled it using new Irwin bits and a carbide bit, but ended up just pushing it down and buggering up the threads. Later I will try installing a metric stud that is slightly bigger. For now, I hope the Holley cast aluminum cover is stiff enough to not require that stud.

    In case you wonder about the harnesses in the photo, I have a Holley Projection TBI and Crane Cams electronic ignition.

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    Last edited: Jul 25, 2011
  2. BillGrissom

    BillGrissom Active Member

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    Update.

    As always, I am overly optimistic until rubber meets the road. In this case the smell of burnt rubber as a worse leak dripped on the exhaust manifold. Kept the mosquitoes away.

    I removed the valve cover, which was simple this time since no RTV gunk on everything. Investigating further, I found that the cast valve cover would rock on the head with no gasket. I held a metal ruler on the head and found it fell away ~1/8" at the rear where it always leaks. The high point was at the broken stud, so I don't really need clamping force there anyway.

    I tried adding RTV between the valve cover and gasket to make up the gap. I made the mistake of snugging the nut at the rear first (low point). After tightening all nuts ~30 in-lbf, I found the cover had partially cracked at the rear tab. I guess it didn't like bending to make up the gap.

    Drove it that way for a day, then cleaned the oil w/ gasoline and alcohol from the outside and squashed RTV under the gasket with a putty knife. That was my traditional fix and will have to serve for now, since the car is a daily driver.

    Conclusions.

    The silicone rubber gasket appears a fine product, but gasket quality doesn't seem to be an issue. The new gasket is worse in one way, which is that it doesn't compress as easily to take up a gap as do traditional rubber composite and cork gaskets. Pure RTV alone may be best in these cases, but is a mess to remove later.

    The main problem we are fighting is bad designs. The factory left the gasket seating surface as a thin sand casting, with no final machining. It wasn't too many years since they went to OHV from flat-heads so maybe "teething issues" on valve cover design. Next time you remove your heads, check if the shop can (inexpensively) machine a smooth, flat surface for the valve cover. Don't remove too much since the oil level is pretty close to the gasket. Also, grind off any casting flash that prevents the oil from draining back, which seemed to be a problem on the other head.

    New engines have greatly improved gasket designs. My 1996 2.4L Mopar has a cast cover with a groove for a silicone gasket. Similar to an O-ring design, you get metal-metal contact and the gasket compresses into a defined groove space. My 2002 3.8L Mopar is an older design, apparently a direct descendant of the LA and Magnum engines. It has a stamped steel cover and gasket similar to my 383. However, the silicone gasket seats on a large flat spot around the head, with hard plastic "compression limiters" at each stud. Much improved, but not as good as the 2.4L. Of course if you install after-market aluminum heads, you will get most of these features, but they are costly and often require significant changes to the valve train.
     
    Last edited: Jul 27, 2011
  3. commando1

    commando1 Mr. Normal FCBO Gold Member

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    The only ones I have found not to end up leaking are the cork impregnated rubber composite with blue silicone applied to both sides. Drastic, but I hate redoing things over and over...
     
  4. polara71

    polara71 Old Man with a Hat

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    Like buying and selling cars...
     
  5. commando1

    commando1 Mr. Normal FCBO Gold Member

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    Being addicted to crack and having a mistress would be cheaper....