Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

There is an extended finger on the lock out latch for the exhaust valve. If you press on it while the engine is running, it will delay the release of the open valve. The feeler guage blade just adds an adjustable pressure to the finger. The more pressure on it, the more delay until it releases, and the slower it runs. The thickness of the blade affects how sensitive the adjustment is.

I often wondered what that finger was for; now I know! But maybe Jin could tell us what it was for.

A pic below shows the blade on the finger.