Jim,
This is Kevin's dad, John. The "Austrian" 0-6-2t at Omaha's Henry Doorly Zoo is equipped with inclined slide valves of outside admission.
While memory of details is dim just now, in the absence of a photo, the front pin of the radius bar connects with the back end of the valve rod via the hanging swing arm of the Helmholz section of the gear. This swing arm looks something like a stretched horse's bit with a "Y" at the lower end for pinning the radius bar to the valve rod. Wish we could post a photo here.
This arrangement is made possible in part by the low position of the valve rod, the result of the inclining of the steam chest. To help visualize, the steam chests are arranged at an approximate 30 degree angle, outward. As you stand beside the engine, the steam chest covers face you. Additionally, the cylinder castings are fully reversible and may be used on either side of the engine!
Most certainly not an expert, and again dim detail memory of earlier readings just now, the Helmholz modification to the Walschearts standard design (if ever there was such a thing, per se) allowed use of a straight link which bore the benefit of simplified machining, a decided advantage in certain cases. Unfortunately, it's exactly what the hanging connection at the valve rod/radius bar does which slips my mind completely just now, or nearly so. If memory serves, it's something to do with the lead, but I'm probably mistaken. I know this much: It "makes up" for the loss of the effect gained by the circular radius of the normal type of link.
At any rate, ours is a direct gear, outside admission locomotive. The eccentric crank leads the main crank pin. It's inclined to the rear of the loco when the main crank pin is located at the bottom quarter.
Recall, direct motion is one in which the movement of the radius bar is the same as the eccentric rod. With indirect motion (such as often seen with locos in which the radius bar is lifted into the top half of the link for forward motion, rather than the reverse as usually seen), the movement of the radius bar is the opposite of the eccentric rod.
These things are SO often difficult to visualize. Too bad there are so few of the valve gear models long ago utilized in many, many schools.
Let us know if we can send pictures of this gear arrangement, as well as the engine itself.
John
