VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Silicone Rubber Valvecover Gaskets

I had a 1975 Chev Camaro from new and instead of having valve cover gaskets, RTV or silicone rubber was used to seal them. I think this practice was dropped but I don't know when or why. Is there a reason other than correctness that this couldn't be used on older engines?

Hi old216,

I can think of a few. The old engine parts did not have the special crease in them that the engines that use the RTV have. If you observed a valve cover for an engine designed to use RTV for example, it has a crease that will retain the RTV and not let it all get "squeezed" out. In older engines there is a specified clearance between the cover and the item to which it is attached. For example, the oil pan/sump must have the correct thickness gasket which was part of the equation of the dipper extension into the oil trough. That's a couple of quick ones.

Beginning in 1987 Chevrolet (and many others) got smart and began using a silicone rubber formed gasket.This has been the most sucessful type of valve cover gasket as yet.The cover-&- head surfaces are designed as not to have the head "cut thru it" they are expensive but on todays hard to work on cars they are a must.On the old solid lifter engines it was customary to remove the valve cover and adjust the the valves every 5000 miles so the gaskets never got old.And they were just plain cork.They newer cork and ground up neoprene gaskets work well-at least the oil won't seep right thru the cork as the old ones did.

Thankyou both for the information. I was curious as to why Chev gave up on that technology. I could never understand how a dealership/garage could afford to do without a bay for half a day while the silicone set up.

I have also heard it said that silicone rubber should never be used in these applications becaue it can break off and travel down to other places.

I have just read your post in "Schools in Session" about RTV. I wonder if that is another reason why Chevy gave it up!

It was also difficult to lay a bead of silicone on a valve cover and try to get around all the obstructions when installing it without disturbing it.The RTV sealeants have also been improved from what was used in the 70s.Most just redid them with gaskets back then-problem solved.Also when the O2 sensor was used (1981 & up in the US) the use of RTV became a problem because if it was injested thru the intake it could foul up the sensor

It can be done successfully (use rtv as a valvecover gasket) for old sixs, if you can't find a real gasket, a Fillipino friend of mine showed me how they did it. spread a uniform bead around the clean oil free head, flatten it down to about 1/8"high and 3/8 inch wide, let it set up, then spread the second bead over it, coat the edge of the valve cover with a light coat of motor oil, carefully set it on the head over the rtv, only thread the acorn nuts on till they touch the rtv, let dry overnight then the next day, tighten down the cover. When folks have to depend upon their minds I am surprised with what they can come up with.

But why not use all those good cork valve cover gaskets hanging on the shop wall? Work better and so much easier.

If you have not noticed by now I have many reservations about using RTV. It does have it's place in the shop if used correctly and carefully.

Ray, you, JYD, Donald, Chevy Nut and I probably have more gaskets hanging on the wall than some of our friends in Australia, Denmark, Sweden, Japan, and in the Far East that do have old Chevrolets and also those new first time owners here in the USA and Canada combined. The fellow that showed me how he used RTV never saw a catalog from the USA or a Chevrolet dealership in his life, but he did have a 1940 Chevrolet powered truck, That is still probably chugging around on Luzon.
I do have a RTV did someone wrong song, story.
One of our company mechanics used rtv to seal the gas tank gauge sending element in an auxiliary tank, about 3 days later the truck quit running. It has blue RTV minature cylinders plugging the carb float valve, they were covering the holes when he screwed in the machine screws and remained intact and migrated to the carb fload valve.

I used to use the RTV in a similar manner only using 1 coat. I would flatten it out some, let it set up until it was stiffer, carefully install the covers, start the bolts and the next day I would snug them up. I don't know how a garage could do this in a more reasonable time.

I would like to know the technique for making holes in cork gaskets. The only method that I could come up with would be using a piece of tubing as a punch?

Old 216,there are hole punches on the market for a good price,with several sizes in a kit, I usually use the pan or rear end inspection cover for a pattern and punch thru the mounting holes, then use a old gasket or a ready made gasket for a pattern to cut the inside out. punch the hole to let the bolt threads just slip thru.
Another method for paper gaskets is to use a ball peen hammer to cut the edge of the gasket (pound on the paper material over the edge of the block or housing) and a small round end of the ball part to tap out the hole right over the bolt hole, just don't let the cut out part plug the hole or hit too many licks and bugger up a threaded hole. , like in the engine block or differential housing.

MrMack,
thanks for the tips.Some things are so much easier when you know how!