I had occasion to open up our Great planes GP-42 engine and noted that some to the fuel/air passageways between the liner and the case did not line up. I did ensure that the slot in the top of the liner is aligned with the pin in the case, so I know the liner is in correctly. In one area, there was well over 1/16th of an inch where the overlap in the case reduced the opening in the liner.

The engine will be replaced soon with a PRO-46, so the GP-42 is available for play/modification. I was looking at trying to increase the airflow inside the engine by porting the case to match the liner. There are also some sharp casting lines and corners that look like they should be cleaned up too.

My feeling, from working on automotive heads, is that if I can clean up the flow, without touching the port sizes, shapes, etc., the engine should be able to breathe better and therefore make more power.

Has anyone ever ported these little engines? Is it worth the effort? I just see so much that is hindering good flow; it just seems like a shame not to clean it up.

Jack