I've been building a Model Maker steam engine from solid billet (no castings). I have deviated from the blueprints by adding reversing gear to the engine. I have set up temporary adjustable valve rods to try to determine the best length. While I have equal travel of the valve...I'm finding that I'm not getting full steam port exposure with the valve moving top to bottom. I'm guessing there's really two ways to make adjustments to this..one: mill off the top and bottom of the actual valve block or two: make new eccentrics with a slightly larger throw. I'm a bit concerned with milling the valve...my thought is if I mill too much..I may not get adequate coverage of the ports during exhaust. It seems remaking eccentrics with about .060 throw might give me the port open g I'm looking for. Any thoughts or recommendations of options or concerns would be appreciated.
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Are you saying the slide valve should be 20% of the port opening overlap when the slide valve is at midpoint?
The lands on the slide valve need to be about 20% wide than the inlet ports. No wider. it also looks like your slide valve is very long by comparison with the ports.
At midstroke, both inlet ports should be covered (rule of thumb, this is adjusted to allow early inlet in practice) with excess of the valve face covering by the approx 20% at each extreme end.
Looks to me like you need more throw. you want to open the inlet port enough but not close the exhaust port at the same time.
Can you show us the uncovered port face?