Cox TD pipe

That was used as a pressure tap in some installations. The plastic nipple needed to be drilled out with a tiny drill. It was hard to keep a pressure line attached here, so it was used very little.
Bill

It's a fitting for a crankcase pressure tap, not normally used for R/C or FF. Used for controline speed models.

If you plan to use this engine DO NOT drill out the tap. It will provide crankcase pressure which is way too high for any use other than certain applications that require more power. If you need more power get a more current designed engine like the Norvel or other similar powerplant that isn't a 40 year old engine design. They will run circles around the TD but I still like my TD's anyway. I just noticed you don't know the displacement If it has a small band around the Base of the piston when you look through the exhaust port ( Piston at TDC) it is a .051 If there isn't any grove on the piston it is a .049 This was done so that it was easy to confirm the displacement at model contests since 1/2 A went to .5 and the A class was above. This was handy so that you could fly the same plane in 1/2A and A free flight at a contest. I was so poor back then I would just change piston and Cly and not do the engine swap. Sparky