wa371@sdcc12.UUCP (wa371) (04/07/85)
The best gasket cement is silicone rubber cement. It is sometimes
sold as bathtub caulk and for other purposes, but it is the same stuff
if it says 'silicone' and is very rubbery when cured. It will permantly seal
anything, especially such problem areas as valve covers
and oil pans.
The Corvair for example was a notorious oil leaker. But my Corvair
engine, sealed with silicone rubber cement, never leaked a bit of
oil.
How to use silicone rubber cement: Clean the mating surfaces of oil
and grease. Wiping thoroughly is sufficient. Then apply a thick
film to both sides of the gasket and let it set for about 10 minutes
until it is no longer sticky. Then bolt the parts together.
The gasket can be omitted altogether. In that case apply the film to one
of the mating surfaces.
Any color silicone rubber cement will do, but I
prefer white, because that makes it easy to see the thickness of the film,
when I spread it with my fingers. With correct thickness about 1/16 to
1/8 inch will squeeze out the sides when the parts are bolted togther.
Silicone rubber will withstand up to 500 deg F. It seals against
all oils, water, air and vacuum. But it is useless for fuel, because fuel
turns it into a soft jelly. It is not very strong by itself, and
most oils soften it a little too. It must therefore be confined between
mating surfaces and have time to cure (one day or more) before it
can withstand greater pressures.
That reminds me: I once had a hole in a radial tubeless tire, the diameter
of my little finger in the shoulder area, where even small holes can
not be sealed because fo the extreme flexing.
You guessed it. Silicone rubber cement to the rescue. I applied it 1/4 inch
thick over the hole on the inside of the tire after sanding.
Then I let it cure for a week for maximum strength. I drove on that
tire for another fifteen thousand miles before it started to leak again.
I am sure that a patch over a smaller hole or in a place with less flexing
would have outlived the tire itself.
This is not a practical way to fix flats on a trip, unless you have
lots of time {:-) --and know how to get the tire off the rim without tools.
(If you want to know how to do that, write to me.)
Bernd 'bear-nd' *** hooray for USENET ***
(Not affiliated with, nor speaking for U.C. San Diego)
UUCP: ...!ucbvax!sdcsvax!sdcc12!wa371, ARPA: sdcsvax!sdcc12!wa371@noscjackh@zehntel.UUCP (jack hagerty) (04/09/85)
> Any color silicone rubber cement will do, but I > prefer white, because that makes it easy to see the thickness of the film, Not true! Silicone rubber is wonderful stuff, but it comes in different compositions for different purposes and use of the wrong one could be disasterous. The clear and white types are sold as "bathroom caulk" or "glass sealer" and are good for just that. Around a car they can be used to seal leaks in your doors, windshield, trunk, etc. but they don't have the heat and chemical resistance to be used around engines. To seal oil covers, you need "engine gasket" type silicone. The one marketed by Permatex is blue (I say marketed because it's actually made by GE). This type is temperature resistant up to 400 F and also resists oils and other automotive chemicals. For higer temperatures, such as sealing exhaust systems, etc., use "High Temp" silicone. This type is colored red and is resistant up to 500 F. Some confusion is possible because GE's color for their "normal" engine silicone is also reddish orange. Be sure that any silicone you buy for this purpose is clearly marked "High Temp". GE has also come out with a very specialized type of silicone recently. It is a clear, glass sealer type, but the twist is that it's "flowable". It seems to be the same gooey stuff as any other silicone, but the surface tension is very low and it continues to run and flow into tiny cracks and holes. I used it last fall to seal an 8 year old leak in my Alfa's doors (that had resisted all conventional sealants including standard clear slicone). It was wonderful, not a drop all winter! -- Jack Hagerty, Zehntel Automation Systems ...!ihnp4!zehntel!jackh