Gasket Making

In many situations you may need or want to make your own gaskets for your boat's engine or other equipment. It may be difficult to find a gasket for an older engine, especially when you're cruising and the need arises suddenly. You may also enjoy doing it yourself and saving money.
This photo shows the inside of a cover plate for a 1980 Paragon transmission, which was installed with certain Yanmar and Westerbeke marine diesel engines. The Paragon company no longer exists, and parts can be difficult or possibly impossible to find. In this case, this sailboat owner needed to replace the original paper gasket between this cover and the transmission case, which had disintegrated when he opened the transmission cover to make a clutch adjustment.

Gasket material is readily available at almost all automobile parts stores and costs little. Buy the type of material that most closely matches the original gasket (whether paper, cork, rubber, or some other material). In most cases it won't matter if the gasket is a little thicker than the original, but be sure it meets the needed specifications (i.e., that it will stand up to engine heat or fluids, etc.).
In this photo, the boat owner chose a thick paper gasket with a light adhesive backing that will make it easier to mount the completed gasket.
The first step is to obtain an accurate outline of the gasket from the shape of the surface on which the gasket will lie. A simple way to do this is place the object (like this tranmission cover plate) on the gasket material and lightly tap it with a mallet.

If you look carefully at this photo, you can see the indentation made in the paper gasket by the edges of the plate when tapped with the rubber mallet. Often you can simply cut along these edge lines with sharp scissors, but this owner decided also to outline the outside edge with a market to make the cutting easier.
Sometimes, especially with thinner gasket paper and sharp metal edges of the piece to be gasketed, the tapping actually cuts through the gasket paper so that cutting with scissors is not needed at all.

Here is the gasket after it has been cut to fit the outlined edges of this transmission cover. (The gasket looks slightly smaller than the cover because of the camera's foreshortening due to the height of the metal cover.)
Note that in this case, using thick gasket material, the edges of the gasket are a bit rough from the scissoring, which is not usually an issue with thinner paper gaskets or those made of other materials. If this happens to you, be sure to neaten up the gasket's inside edges with a sharp knife before installation to ensure small bits do not break loose and fall into the engine or other part.
Overall, making your own gaskets is more satisfactory than using a silicon paste that hardens into a gasket after being applied to the edges. It is very easy to apply too much silicon, resulting in extra material inside the part that can break free and clog up the works, or to have gaps that allow fluid leakage. A well-made gasket of the right material prevents such problems and takes only a few minutes to create.