Valve Timing

Stephenson

Ian wrote on Little Engines Yahoo Group:

When the reversing lever (Johnson Bar) is in mid gear position there WILL be movement of the valve spindle however it will be at a minimum.

With the covers off the valve/steam chest then with the lever/bar centred (mid gear) the valve should just open the ports and it should be symmetrical at top and bottom dead centre respectively.

Better to set the eccentrics at full gear so that the valve only just cracks the ports at TDC/BDC and adjust the spindle length or slide position so it is symmetrical. just as you would a non reversing engine. This adjustment can be done without taking the cover off if the boiler has some low pressure air it and tubes connected to the drain cocks are led into a jar of water. Bubbles from the tube indicates the port is just opening.

References

• "Valve Gear and Valve Events"
• "Steam Engines", Project Gutenburg
• "Cylinder Design", The Great Western Archive
• "The Mechanics of the Miniature Steam Engine
• "Steam Engine Indicator Diagram"
• A Few Useful Shop Hints On Locomotive Valve Setting
• One thousand pointers for machinists and engineers..., see page 90 for valve timing
• "Steam Engine Pressure-Volume Diagram"