Wow, Dan! Very interesting. Might be a dumb question, but is there some characteristic of this part that makes the port repair tool necessary? The tool looks like something you planned for in advance.
Dennis, yes the port repair tool was part of the plan. As this is a small cylinder the grid is 1/4" the way I made the curved port cores it did not leave much room for the gasket to seal the covers.
This is actually a 7/8ths scale Shay cylinder which is why there an extra mounting face. I plan to make a bottle frame engine first for a test.
Here is a photo of the port face, and the mounting face. I was having problems with the mounting face dishing in so I added the samll plate to make that section thinner which is exactly what the Lima Works did and where I got the idea.
The port cores are made from stacked sheet metal. The ports are 0.040" with the exhaust a double thickness and the bridges are 0.050"
The port core block has counter bored screws that act as stops so when the block is pulled out of the wax it only travels far enough to clear the wax model.
Manfred, Thanks for the photo. This engine is a freelance design from a few photos of the type and the one you posted is what I am shooting for.
Pat, mostly I use vulcanized rubber molds just like the jewelry trade. I never had any luck with a cylinder with a core for the bore only. The thicker section was caving in with both the wax injection and the metal casting. I finally went to a fully cored cylinder very similar to the original design and the shrinkage problems were solved because there were no longer any thick sections to cause problems.
The port repair tool fixes the end so a full cover gasket is used. There might be another way to core the steam passages but this is the simplest method I could come up with.