Q-talk 107 - Oil Leaks - Gaskets
- Category: Q-Talk Articles
- Published: Wednesday, 23 December 2009 16:24
- Written by Dave Richardson
- Hits: 2535
To explain the fuel dripping from an SR71 while on the tarmac, have you ever heard someone simply state, "Well, it's an SR 71."? Granted, the slide rule toting designers of the Blackbird allowed room for expansion of the exterior surfaces, including the fuel cells, caused by the friction of the air molecules hitting the plane at supersonic speeds. Until recently, I thought the same sort of glib answer was true for VW engines that leaked oil. The explanation was, "Well, it's a VW", as if oil leaks and VW were synonymous.
This all came to light when I was doing some spark plug work on my Revmaster. Those of you who are familiar with the Revmaster engine know that you access the two lower spark plug hole covers by removing the valve covers. This metal-on-metal contact point requires a good seal because there is so much oil being tossed around by the rocker arms. I understand there have even been fires in this area from oil coming in contact with heated metal. As a sealer, I originally used some high temp red silicon. Then I tried the brown Form-A-Gasket when reassembling the covers. It seemed this combination created more of a leak than ever. I mentioned the problem to Terry Crouch and he asked how I cleaned the metal surfaces. I told him I wiped everything down with paper towels before applying the Form-A-Gasket to both surfaces. He asked if I was sure I got all the oil off the metal and I said, " I rubbed pretty hard with the paper towel." Then he asked a question that turned a light bulb on for me. He asked, "Could you have painted on those metal surfaces?" I had never considered getting it that clean. He said the best thing to do was to use a solvent, like lacquer thinner, to be sure all traces of the oil was removed. Then it would be fine to put a small, continuous bead of gasket sealant around the side of the cover where the two metal pieces touch. He suggested following the instructions on the sealant box to allow time to cure.
I asked Terry for a good way to remove the old Form-A-Gasket. He said the common practice was to remove as much of the material as you can with your hand. Then a razor blade, held at 90? relative to the surface, could be scraped across the area to remove any remaining debris. I tried this technique and it worked really well for under the valve cover, primarily because the area was so accessible. I was concerned, however, about using the razor blade around the lower spark plug cover holes because the spark plug wires were so close to the surfaces. I needed a way to still use the basic idea but alter it protect the wires. I remembered a trick I saw several years ago while in college. In a science class, I observed an ophthalmologist dissect a cow eye. In preparation for his initial incision, he pulled out a standard double edge razor blade and gripped it with a small locking clamp/forceps. He placed the blade against the table, covered everything with a small towel and with his free hand over the towel, he twisted the clamp to snap off a portion of the blade. Voila'! He had a custom-sized disposable scalpel.
With safety glasses in place, I tried my hand at making my own miniature tool. I snapped the corner off of a single edge razor blade, producing a new 3/8" scraper. Then while holding the small blade with a similar clamp/forcep as to what the doctor used, I was able to maneuver around the spark plug holes. As long as I was careful, the wires were not in as much danger. Pretty slick! Please use EXTREME caution if you try this technique yourself. Flying bits of razor blades WILL do damage.
I tried a couple of new things when I reassembled the spark plug and valve covers. Rather than using the Form-A-Gasket, I used Permatex Hylomar HPF gasket dressing and flange sealant - item number 25249. The company claims the temperature range for this dressing is -60? to 600?F, which is well outside the expected range that the heads should experience. After scraping and cleaning all the surfaces with lacquer thinner, I put a bead of Hylomar around the parameter of the spark plug covers and put them in place. I also put a small amount of the Hylomar at the base of the screw heads that hold the covers in place. This accomplishes two things. 1) It helps to seal any holes found around the screw heads and 2) It helps to keep the screw from backing out.
Again, after talking with Terry Crouch, I am trying a new way of preparing the valve cover flanges. I am using a spray-on gasket sealer, also from Permatex, called HighTack Spray-A-Gasket Sealant - item number 80064. After scraping and cleaning the flanges with lacquer thinner, I applied a thin coat of the Spray-A-Gasket to the valve cover flange and the gasket material. I let them both dry thoroughly per the instructions. Terry felt this was important before positioning the gasket. He suggested hanging the cork gasket with a string and spraying a light coat on both sides to get the best seal. The nice thing about the Spray-A-Gasket is that any of the red overspray cleans up easily with the lacquer thinner.
Terry also said with the cork gaskets that you can actually clean both the head and the valve cover with the lacquer thinner and apply the cork gasket dry and get good results. I'll have to give that a try down the road.
While there are many other ways to achieve the same objectives, this process has worked much better for my engine. The leaks that I was seeing are gone and I can now feel comfortable putting on the cowl again. I am not as worried oil seeping out and becoming a source of combustion.
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