Motorstar NA: Radial Aircraft Engine Sales And Service

The R-263 project is continuing, but not at a pace we had hoped. The initial design was base upon using modified M14P cylinders. We built up several engines and ran extensive tests. These included using an Ellison carburetor, and finally a fuel injection system similar to the Continental system.

During the engine tests an important objective was not reached. The specific fuel consumption was too high and we were not able to achieve the horse power expected for an engine of this displacement.

We tried different cam disk and intake modifications but without success. Many hours were logged on the test stand and after a lot of measurements we found the problem. The shape of the burning chamber of the cylinder head required the increase to the top of the piston in order to have the proposed compression ratio. This resulted in a larger distance to the first compression ring and the mixture doesn’t burn properly on this zone. The only solution would be to design new cylinders and pistons.

We have decided to use the cylinder assemblies from the O-200 engine as they have a similar bore and stroke. The added benefit is that they are readily available and relatively inexpensive.

This has required some significant changes to the basic design. It was necessary to relocate the cam disc from the front of the engine to the rear. The Continental design has the push rod tubes on the same side as the exhaust. This also requires a different rocker arm as we must use solid lifters with the roller type of cam follower. This means a new rocker arm assembly.  

The factory is making these changes now and we expect to begin testing again  in the spring.