Crankcase Ventilation

When the engine is running, some of the combustion gases slip past the piston rings into the crankcase. This causes the pressure inside the crankcase to increase which can impede oil flow. The combustion gases can also reduce the lubrication effectiveness of the oil.

There are a variety of solutions that can be used to release these crankcase gases, but we wanted to do something that was relatively simple and would work with well with the rest of our engine design.

One of our valve covers has an oil filler tube with a fitting for a vent hose. Normally, this would be connected through PCV valve (positive crankcase ventilation) to the intake manifold. The partial vacuum in the intake manifold will keep the crankcase at a slightly negative pressure, improving the piston ring seal.

A traditional PCV system is not practical with our engine, however. The TWM system does not have a common intake manifold. Instead, it has an isolated manifold for each cylinder. We do have a vacuum hose connection from each cylinder intake manifold to a shared manifold so that the fuel injection computer can estimate engine load, but this is not designed to be shared with crankcase ventilation.

We were also concerned about simply putting a breather cap (filtered vent) on the oil filler since we did not want any oil mist to leak out onto the engine. Since we had to remove the oil baffle from the valve cover, we were also concerned about oil splashing out a breather cap.

The solution we decided to use was an oil overflow tank. This is a small tank that is connected to the oil vent fitting with an oil hose to catch any oil that makes it's way through the fitting. It has a breather to allow crankcase pressure to be release. It also has a stop-cock on the bottom to drain any oil that gets this far.

We also found a rubber oil baffle that fit into the oil filler tube to reduce splashing into the vent hose.