I am sure it would be fine, but I have also heard horror stories about RTV on pumps / motors / hydrostats which is why I thought I would focus on using the Aviation form-a-gasket No.3. When you said stick with form-a-gasket, I assume you meant the Aviation form-a-gasket No.3 like I mentioned in my original post.
In my search for the part, I did come across a guy that focuses just on the the older cubs and he said that thickness does matter. I also suspect the group is right about finding the appropriate material that is made to handle the oil so I will go on a search tomorrow for the correct gasket material and thickness. Better safe than sorry, sometimes I just need somone to keep me on the right path.
Thanks everyone, feel free to keep adding comments. My mind is like a sponge, I am happy to keep absorbing whatever wisdom you want to bestow on me.
Here are my thoughts. Your mileage and decisions may vary, but I think my experience has some value for what you are doing.
I've made a lot of gaskets. My dad made gaskets and taught me. It can be very tedious - especially the holes .... for holes, I use several hollow punches or ball bearings on a hardened steel plate with various holes with sharp edges. i've made a whole lot more scrap than I've made good gaskets. The thin material is especially difficult.
I think that the thickness does matter - in some cases, the gasket thickness is included in the shims that determine the bearing preload. Of course that means the gasket thickness is only important if the preload is important. In old style manual transmissions with ball bearings the preload is not all that important. In front axle assemblies or even rear axles that that have tapered roller bearings it is.
In pumps for hydraulics, and for the hydrostatics transmissions the gasket thickness not only matters but is critical. Their gaskets are often thin metal sheet that are stacked in layers to make a specified thickness. Soft metal is used without a sealant. There the gasket thickness affects the clearance of the pump rotors and directly impacts the output pressure.
Gasket paper is oil resistant. Check to see if your file paper is. Otherwise I would order the thin gasket paper.
As for RTV, I like your idea - especially when you emphasize "very thin". I have used high temperature RTV for gaskets for 50 years now. I've never used the product that 5030 recommends, but he seems at master craftsman. Most people with his level of machine shop knowledge are. So it is worth looking into.
I use a different product now. It is based on my work on instrumentation. Dow 3145 - can be ordered online. Shorty's Pilot shop is where I got mine. A 3oz tube will damage a fifty dollar bill. Treat it right and that will last for years. Lots of uses.
. It is expensive and superior to anything you can buy automotive-wise. FWIW, There are two RTV (Room Temperature Vulcanizing) curing chemistries. Both use water from the atmosphere to initiate curing. One - the common commercial type - outgasses acetic acid as it cures. Smells like strong citrus.
The other - the Dow 3145- does not have an odor or acid interaction. It is also safe on skin.
The complete description is DowSil 3145 Mil-A-46146 Adhesive/Sealant. It is an RTV using the second type of curing which is a moisture-activated platinum cataylst. The cured 3145 is good for high temperatures, flows, may be smoothed with a moistened finger, is more adhesive, and stays flexible for years. You can let it cure more completely or even completley before mounting the gasket IF IT IS ONLY A THIN LAYER. It retains enough flexability to be mounted when cured.
The trick with RTV is you never want to assemble it wet. The perfect assembly would be to wipe the gasket on both sides with a layer of RTV no thicker than a coat of paint. All you want it for is a little strength and a little ability to fill a microscopic defect in the casting. Then let it cure until it it no longer able to moved or sticky to the touch. For 3145, smooth with a moistened finger. With 3145 You can do one side of the gasket or case, let it cure, and then do the other. You want more than a surface cure. You don't want to compress it and have liquid RTV bead out the sides. This amount of takes half an hour to an hour - it is dependent on humidity.
Then I assemble and torque half way. I then give it another few hours and torque all the way. It won't hurt if the RTV is a little too cured, but can be a disaster if not cured enough or too thick.
Just some thoughts... hope they help.
rScotty
