HALF-SCALE GARDNER: Building a half-scale Gardner Model 0 engine, Part 2 of 2

Gears and eccentrics

The kit of parts included two cut gears, with the only work necessary being to drill and tap the smaller gear for a lock screw above its keyway. The main gear was mounted on a bronze bearing mounted on a shaft fitted to the engine block. A spiral oil groove was cut in this shaft to help lubrication. The stub for this shaft fitted in the engine casting and it was turned 0.037 inch off center, thus providing a means to adjust the backlash and the degree that the two gears meshed.

The two eccentric straps were machined from the supplied castings and their holding discs were turned from 1.125-inch-diameter steel, with the hole for the shaft offset by 0.125 inch. These holding discs were fitted either side of the main gear wheel, and all shared the same bearing.

To complete these eccentrics, pushrods were made threaded at both ends with connecting eyes made for one end of the rod. The pushrods were made fractionally longer than the plans to provide plenty of scope for them to be trimmed and adjusted after assembly. This would take place when viewing their operation when setting the valve timing.

To shape the pivot rod eyes, filing guides were made, namely a narrow disc of steel turned to the radius needed at the end of the eye. A stub on the disc fitted the lateral hole in the eye. For repeat operations, these guides could be hardened for durability, but this step was not taken for this “one use” application.